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The effects of salinity and added substrates on growth and survival of Metapenaeus monoceros (Decapoda: Penaeidae) post-larvae
Aquaculture 196 Ž2001. 177–188 www.elsevier.nlrlocateraqua-online
The effects of salinity and added substrates on growth and survival of Metapenaeus monoceros žDecapoda: Penaeidae/ post-larvae M. Kumlu a,) , O.T. Eroldogan a , B. Saglamtimur b a
Faculty of Fisheries, CukuroÕa UniÕersity, 01330 Balcali, Adana, Turkey b Faculty of Fisheries, Mersin UniÕersity, Mersin, C¸ iftlikkoy, Turkey
Received 28 May 2000; received in revised form 27 October 2000; accepted 10 November 2000
Abstract This study was carried out to determine the optimal culture salinity and to investigate the effects of added substrate on growth and survival of Metapenaeus monoceros during its nursery culture in two separate experiments. In Experiment 1, at the end of a 50-day culture period, post-larvae ŽPLs. reared at 5, 10, 20, 30, 35, 40 and 50 ppt displayed 8, 11, 48, 49, 52, 59 and 36% survivals, respectively. Daily growth rates at salinities above 30 ppt Ž0.266–0.320 mm dayy1 . were about 5-fold higher than those obtained at salinities below 10 ppt Ž0.035–0.056 mm dayy1 . Ž P - 0.05.. Total lengths ŽTL. at 30, 35, 40 and 50 ppt were 19.09, 18.97, 19.09 and 18.89 mm, respectively Ž P ) 0.05.. Mean wet weights acquired at 30–40 ppt Ž63–71 mg. were 7–8 times higher than those at 5 and 10 ppt Ž8.12–9 mg. Ž P - 0.05.. A rise in salinity resulted in a drastic increase in biomass Žover 50-fold. from 0.018 g at 5 ppt to 0.927 g at 40 ppt. Hence, optimum salinity for the nursery culture of M. monoceros PLs appeared to be between 30 and 40 ppt at 288C. In experiment 2, Group A received no additional substrate while the other two groups had added substrates consisting of wooden frame with vertical ŽGroup B. or horizontal ŽGroup C. plastic mesh. Additional substrate increased habitable surface area approximately 330%. Percentage survivals in Group A, B and C were 71, 70 and 63%, respectively. TL was significantly lower in Group C Ž15.65 mm. than in either Group A Ž17.71 mm. or Group B Ž17.23 mm. Ž P - 0.05.. The PLs in Group A attained a significantly greater mean final weight Ž62 mg. than those Ž40–55.14 mg. in both treatments containing artificial substrates. The PLs in Group B and C had
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Corresponding author. Tel.: q90-322-338-6893; fax: q90-322-338-6439. E-mail address: [email protected] ŽM. Kumlu..
0044-8486r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 4 - 8 4 8 6 Ž 0 0 . 0 0 5 8 0 - 9
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12% and 40% lower biomass than that in Group A. The current results demonstrated that the use of either vertically and horizontally placed substrates do not provide any advantage during the nursery culture of M. monoceros. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Metapenaeus monoceros; Post-larvae; Salinity; Substrate; Penaeid; Growth
1. Introduction Salinity is one of the most important abiotic factors influencing the growth and survival of aquatic organisms. Penaeid shrimps are mostly exposed to rapid salinity fluctuations and extreme environmental conditions in estuarine areas during their early life cycle ŽRaj and Raj, 1982.. Hence, in contrast to adults, the post-larvae ŽPLs. and juveniles of most of the species are expected to have a great ability to adapt and osmoregulate well at fluctuating salinities. It is well known that salinity affects food consumption, conversion efficiency and, thus growth, and survival of cultured penaeid shrimps ŽStaples and Heales, 1991.. A considerable number of studies have been conducted to determine effects of salinity alone or in conjunction with other abiotic factors and osmoregulatory ability of commercially important penaeid species such as Penaeus monodon ŽCawthorne et al., 1983; Parado-Estepa, 1998., P. semisulcatus ŽHarpaz and Karplus, 1991; Kumlu et al., 1999a., P. aztecus ŽVenkataramaiah et al., 1972., P. setiferus ŽZein-Eldin and Griffith, 1969., P. Õannamei, P. stylirostris, P. californiensis, P. breÕirostris, ŽMair, 1980., P. merguiensis, P. esculentus, Metapenaeus bennettae ŽDall, 1981., P. japonicus and P. chinensis ŽCharmantier-Daures et al., 1988. and P. indicus ŽKumlu and Jones, 1995.. Studies, with PLs of several shrimp species have revealed that optimal culture salinity is species-specific ŽParado-Estepa et al., 1987; Diwan and Laximinarayana, 1989; Kumlu and Jones, 1995.. Therefore, it is important to determine optimum salinity level for each commercial shrimp species in intensive nursery systems where the salinity can be altered according to optimum requirements of a particular species. Being benthic animals, shrimps are constrained to two-dimensional space rather than three-dimensional volume as with many finfish species. Hence, it may be possible to intensify stocking density by adding artificial substrates into culture tanks to increase habitable surface area for the PLs during nursery culture period. Growth and total yield in the freshwater prawn Macrobrachium rosenbergii were significantly improved by adding substrates in ponds ŽCohen et al., 1983; Tidwell et al., 1998, 1999.. However, artificial habitats constructed of seine netting suspended vertically in raceways improved survival but not growth in the marine shrimp P. Õannamei ŽSandifer et al., 1987.. Studies carried out with other species showed that added substrates did not provide any advantage during the nursery culture of P. Õannamei ŽSamocha and Lawrence, 1992. and P. semisulcatus ŽKumlu and Eroldogan, ˘ 2000.. M. monoceros is an Indo-Pacific species distributed along the coast of Eastern Mediterranean and is one of the most important commercial species in this part of the World. A better understanding for the effects of salinity and added substrates during the nursery culture of this penaeid shrimp species is important in order to define adequate conditions for optimal production.
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Therefore, the primary aims of the present work were to determine optimal culture salinity and to investigate any possible advantage of added substrates on growth and survival of M. monoceros during its nursery stages.
2. Materials and methods The effects of various salinities and two types of added substrates on growth and survival of M. monoceros PLs were investigated in this study. For this purpose, broodstock captured from the Yumurtalik Bight of north-eastern Mediterranean were spawned at the Marine Research Station of the University of Cukurova in Adana, Turkey. 2.1. Experiment 1 Larvae of M. monoceros were fed on micro-algae and Artemia until the PL stages. The PLs were reared on live Artemia nauplii and a granulated diet ŽINVE Aquaculture, Belgium. containing 45% protein until PL10. The animals ŽPL10. previously grown at 40 ppt salinity, were stocked in three replicates for each treatment at a density of 25 PLs into each plastic experimental vessel Ž35 = 20 = 15 cm., supplied with a continuous gentle aeration. The PLs were acclimated to seven different salinities Ž5, 10, 20, 30, 35, 40 and 50 ppt. over a period of 2 days by adding well water or aquarium salt ŽInstant Ocean, Aquarium Systems, USA.. The animals were gradually acclimated to the desired test salinities by reducing or increasing salinity by 2–3 ppt, 7–8 times a day from 40 up to 50 ppt or down to 5 ppt. Rearing water was filtered to 1 mm with a sand filter and a series of cartridge filters Ž10, 5 and 1 mm.. All the animals were kept in the final test salinities for at least 8 days before the first sampling carried out on the 10th day of the experiment. The PLs were fed the granulated feed four times daily to excess. Salinity and temperature measurements were performed with a direct reading digital salinometer ŽYSI, USA.. The pH was measured weekly with a digital pH meter ŽWTW, Germany.. Ammonia levels were not measured in the present study. However, in a previous penaeid study, in the same system, at highest loading, the maximum level of total ammonia was 0.175 mg ly1 , which is within the acceptable range for penaeids ŽWickins, 1976.. The experiment, which lasted 50 days, was conducted under a controlled photoperiod Ž10 Lr12 D. with artificial fluorescent illumination and the water temperature was maintained at 288C. Uneaten food was removed daily when 25–50% of the rearing water was renewed. A complete water exchange was performed every 10 days, and simultaneously the PLs were counted and 10–12 of them were measured from the tip of the rostrum to the end of the tail using calipers Ž"0.01 mm.. The PLs were rolled in tissue paper to remove surface moisture prior to weighing. At the end of the experiment the animals at PL60 were weighed on a scale Ž"0.001 g. to determine individual wet weight and total biomass.
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2.2. Experiment 2 This experiment was conducted to investigate any possible advantage of two types of artificial substrates on growth and survival of M. monoceros PLs. For this, the animals ŽPL20. were stocked at a density of 120 individuals into each aquarium Ž30 = 20 = 22 cm. in three replicates for each treatment. The treatment used in the experiment were as follows: Group A Žcontrol. with no artificial substrate, Group B with vertically placed artificial substrate and Group C with horizontally suspended substrate. The surface habitable area, which was 600 cm2 in the control group, was increased to about 2000 cm2 in Groups B and C. The substrates were constructed of wooden squares Ž15 = 15 cm. covered with a course mesh Ž0.5 mm. and placed in the form of a three layer-rack where each layer was 7 cm apart from each other ŽGroup B. or suspended from top of each aquarium in again three layer being 7 cm apart ŽGroup C.. Throughout the 30-day culture period Ž30 days., the PLs were fed the same granulated diet to excess as in the first experiment four times daily. Each day, 100% water exchange was carried out. Water pH and temperature were 8.0–8.1 and 288C, respectively. Animals inhabiting the artificial substrates in Groups B and C were counted everyday at 1000 to 1100 h. At the end of the experiment, all the animals in each treatment were counted and measured for their TL and weight as described in the first experiment. 2.2.1. Statistical analysis Data were analysed using one-way ANOVA and any significant difference was determined at 0.05 probability level by Scheffe’s test after the normality and homogeneity ŽBartlett’s test. of the data were checked ŽSokal and Rholf, 1981. in Minitab statistical software.
3. Results 3.1. Experiment 1 Following a gradual acclimatisation over a period of 48 h, the percentage survivors in 5 or 10 ppt were over 80% on the 3rd day of the experiment. Post-larval mortality in each test salinity was high during the first 20 days of the culture. Yet, although survival was levelled off at salinities above 20 ppt, mortality remained high at 5 and 10 ppt throughout the experiment ŽFig. 1.. Figs. 1 and 2 show that M. monoceros PLs had higher survival and better growth at high rather than low salinities between PL10 and PL60. The lowest salinities Ž5 and 10 ppt. consistently produced high mortalities throughout the experiment resulting in only 8–11% final survivals ŽFig. 1, Table 1.. The highest salinity level Ž50 ppt. tested in this study resulted in only 36% survival as compared to 49% at 30 ppt, 52% at 35 ppt and 59% at 40% ppt. Final survival at 40 ppt Ž59%. was significantly higher than at all other salinities Ž P - 0.05. ŽFig. 1, Table 1.. Growths as TL at salinities below 20 ppt were also significantly lower than those sustained at higher salinity levels Ž P - 0.05. ŽFig. 2..
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Fig. 1. Survival of M. monoceros PLs grown at various salinities from PL10 to PL60. Each symbol is a mean Ž ns 3..
The PLs grown at 5 and 10 ppt displayed growth rates between 0.035 and 0.056 mm dayy1 between PL10 and PL60 as compared to 0.153–0.320 mm dayy1 at higher salinities ŽTable 1.. Final TL at 5 and 10 ppt were 11.5 and 7.18 mm, respectively Ž P ) 0.05.. Growth rates of PLs, which ranged between 0.264 and 0.320 dayy1 , at 30, 35, 40 and 50 ppt were not significantly different from each other Ž P ) 0.05. ŽTable 1.. Total lengths at 30, 35, 40 and 50 ppt were 19.09, 18.97, 19.09 and 18.89 mm, respectively Ž P ) 0.05.. The PLs reared at 20 ppt had an intermediate growth Ž15.07 mm TL and a growth rate of 0.153 mm dayy1 . between high Ž30–50 ppt. and low salinities Ž5–10 ppt.. Daily growth rates obtained at salinities above 30 ppt were about 5-fold higher than those obtained at salinities below 20 ppt. These results show that salinities below 20 ppt slow the growth and produce high mortality during nursery culture of M. monoceros. Optimum culture salinity for the PLs appeared to be between 30 and 40 ppt at 288C. The results of individual wet weight and total biomass also confirmed the above findings. PLs grown at 5 and 10 ppt attained the lowest individual wet weight Ž8.12–9 mg. while those at 30 ppt had the highest mean weight Ž70.54 mg. at the end of the
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Fig. 2. Total length Žmm. of M. monoceros PLs grown at various salinities from PL10 to PL60. Each symbol is a mean Ž ns 3..
50-day culture period Ž P - 0.05. ŽFig. 3, Table 1.. The results showed that mean weight obtained at 30 ppt was 7–8 times higher than that at 5 or 10 ppt. At PL60, final mean weights of PLs reared at 30, 35 and 40 ppt were not significantly different from each other Ž P ) 0.05.. PLs at 50 and 20 ppt had lower mean weights than those at 30–40 ppt Ž P - 0.05.. Table 1 and Fig. 3 show that, at PL60, the PLs cultured at 30, 35 and 40 ppt exhibited the greatest biomass ranging from 0.853 to 0.927 g. The lowest biomass were obtained at 5 Ž0.018 g. and 10 ppt Ž0.031 g.. A rise in salinity resulted in a drastic increase in biomass from 0.018 g at 5 ppt to 0.927 g at 40 ppt. The increase in biomass between 5 and 40 ppt was 51.5-fold. Yet, the biomass showed a 50% decline at 50 ppt as compared to that resulted at 40 ppt ŽTable 1.. Throughout the experiment, temperature and pH of the water in culture vessels were 27.8–28.28C and 7.95–8.13, respectively. 3.2. Experiment 2 The mean daily number of PLs inhabiting the two different substrates was 24 in Group B and 14 in Group C. Hence, it appeared that the vertical substrate was
Salinity
Final survival Ž%. Final TL Žmm. Growth rate Žmm dayy1 . Mean weight Žmg. Biomass Žg.
5 ppt
10 ppt
20 ppt
30 ppt
35 ppt
40 ppt
50 ppt
8.00"3.15d
10.67"2.52 d
48.00"1.00 b
49.30"4.16 b
52.00"2.00 b
58.67"3.06 a
36.00"2.00 c
11.5"2.98 d
7.18"2.25 c
15.07"3.51b
19.09"6.28 a
18.97"3.10 a
19.09"4.16 a
18.89"2.45a
0.056
0.035
0.153
0.320
0.272
0.266
0.264
9.00"3.56
8.12"2.25
37.51"4.72
70.54"8.14
65.50"4.86
63.18"7.70
56.22"3.49
0.018"0.04
0.031"0.07
0.440"0.06
0.870"0.12
0.853"0.09
0.927"0.13
0.506"0.14
Each value is a mean"S.D. Values marked with different superscripts in each row are significantly different from each other Ž P - 0.05..
M. Kumlu et al.r Aquaculture 196 (2001) 177–188
Table 1 Final survival, total length, mean individual weight and biomass of M. monoceros PLs grown for 50 days at various salinities
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Fig. 3. Mean wet weight Žsolid bars. and biomass Žhatched bars. of M. monoceros at PL60 reared at various salinities from PL10 to PL60. Each bar represents a mean"S.D. Ž ns 3 for each test salinity.. Treatments marked with different superscripts are significantly different from each other Ž P - 0.05..
unexpectedly preferred by the PLs. Final survivals in Groups A, B and C were 71%, 70% and 63%, respectively. Table 2 shows that growth as TL was significantly lower in Group C Ž15.65 mm. than in either Group A Ž17.71 mm. or Group B Ž17.23 mm. Ž P - 0.05.. The PLs in the control treatment ŽGroup A. attained a significantly greater mean final weight than those Ž40–55.14 mg. in both treatments containing artificial habitats ŽTable 2.. Horizontal substrate ŽGroup C. resulted in the lowest post-larval TL, weight and biomass Ž P ) 0.05.. The PLs in Group B and C had 12% and 40% lower biomass than that in the control ŽGroup A..
Table 2 Final survival, total length, weight and biomass of M. monoceros reared in various treatments for 30 days Treatments Group A Group B Group C
Survival Ž%. 71.25 70 62.5
Total length Žmm. a
17.71"5.49 17.23"4.46 a 15.65"4.82 b
Weight Žmg. a
62.13"6.91 55.14"8.65 b 40.00"3.65 c
Biomass Žg. 10.19 8.93 6.12
Each value for total length and weight is a mean"S.D. Values in each column marked with different superscripts are significantly different from each other Ž P - 0.05.. ŽGroup A: control without substrate, Group B: with vertical substrate, Group C: with horizontal substrate..
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All these results showed that the use of either vertically or horizontally placed substrates did not provide any advantage over the control treatment during the nursery culture of M. monoceros. In fact, the artificial substrates used in the present study had negative impacts on post-larval survival and growth. 4. Discussion A gradual acclimation over a period of 48 h has been suggested to be adequate for the PLs of P. indicus ŽParado-Estepa et al., 1987; Kumlu and Jones, 1995. and P. monodon ŽCawthorne et al., 1983.. In the current work, this acclimation rate resulted in poor survivals in M. monoceros PLs reared particularly at 5 and 10 ppt salinities during the first 10-day culture period. One may argue that the PLs might have needed a slower acclimation rate than that applied in the first experiment. However, considerably high mortalities observed at all the experimental test salinities including the normal sea water salinity Ž40 ppt. indicated that some other reasons might have contributed to high post-acclimation mortality encountered in this study. The PLs acclimated to 20 and 30 ppt had the highest survivals on the 10th day of the culture. It is known that considerable losses may occur in penaeid shrimps during early nursing culture when the PLs are forced to shift from natural diet to artificial diet ŽFegan, 1992; Ribeiro and Jones, 1996.. It is thought that this might be the main reason why high PL mortality was obtained during the acclimation process. The survival curves showed a normal pattern only after the 20th day of the culture ŽFig. 1.. Most penaeid shrimps are known to be euryhaline species growing in a wide range of salinities at least during their nursery stages. Kumlu et al. Žin press. found that the larvae of M. monoceros from broodstock originating from eastern Mediterranean are good osmoregulators in high salinities rather than low salinities and that the lowest critical salinity was 22 ppt despite an acclimation rate of 4–5 ppt hy1 . Yet, the present results indicate that this shrimp species could neither tolerate low nor high salinities well during the PL stages. Between PL10 and PL60, the animals reared at 5–10 ppt and 50 ppt showed 90% and 65% mortality, respectively, during the 50-day culture period indicating that the PLs of this species were not successful to withstand such extreme salinities. It appears that, to some extent, M. monoceros larvae acquired an ability during the early PL stages to survive in salinities lower than 20 ppt conforming with general life cycle of penaeid shrimps. This agrees with the findings of Charmantier et al. Ž1988. who stated that salinity tolerance of P. japonicus decreased through the larval stages, was at a minimum at metamorphosis, but increased in post-larval stages. An increase in salinity from 5–10 to 40 ppt resulted in a consistent rise in survival, total length and biomass. Despite the fact that P. semisulcatus and M. stebbingi were abundant in estuarine areas in the north-eastern Mediterranean, M. monoceros has never been caught in these areas ŽKumlu et al., 1999b.. These authors captured the specimens of this penaeid shrimp always at depths above 20 m and at normal marine salinities Ž39–40 ppt.. Hence, it appears that unlike other Metapenaeus species, which complete their life cycle ŽDall et al., 1990. or even spawn in estuarine waters of - 10 ppt ŽPotter et al., 1989., M. monoceros from the north-eastern Mediterranean prefers higher saline media even during its nursery stages.
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The present results and studies elsewhere have shown that euryhalinity and optimal salinity resulting in best growth and survival in shrimps differ by species and post-larval stages. Kumlu and Jones Ž1995., and Raj and Raj Ž1982. reported good growth and survival in hatchery-reared or wild-caught P. indicus post-larvae at even 5 ppt salinity. However, the former found that euryhalinity to low salinity of 10 ppt was gradually lost after PL40 and concluded that 25 ppt was optimal for P. indicus during nursery stages. In the current work, between PL10 and PL60, the animals had consistently better survival, greater total length and weight gain between 30 and 40 ppt than at either high Ž50 ppt. or low Ž5–20 ppt. salinities indicating that their optimal culture salinity is in this range. Salinity optima for the larval culture of the same species inhabiting the north-eastern Mediterranean were also reported to be 40 ppt ŽKumlu et al., in press.. Growth rates of M. monoceros PLs at salinities above 30 ppt were significantly higher than the lower salinities Ž5–20 ppt.. Mean wet weights at salinities above 30 ppt were 7–8 times higher than those at 5–10 ppt. Again, biomass attained at 40 ppt was 52-fold greater than that at 5 ppt. It is generally accepted that penaeid PLs grow well in low saline environments and that this low salinity preference might be a useful adaptation to their natural nursery habitats ŽDall, 1981.. Unlike other penaeid species, M. monoceros were not able to adapt themselves to low salinities even at early PL stages ŽPL10-20. indicating that this species is rather stenohaline during PL stages. The PLs consistently showed poor survival at salinities lower than 20 ppt throughout the first experiment. In fact, post-larval growth rate Ž0.32 mm dayy1 . was 5–9 times higher than those at 5 ppt or 10 ppt throughout the experiment. These results indicate that the PLs of this species do not grow and survive well at salinities above 50 or below 10 ppt. Hence, this penaeid shrimp does not seem to be a good candidate for culturing in brackish water environments. For M. monoceros PLs, the lowest and highest critical salinities appeared to be 10 and 50 ppt, respectively. Based on the present results and those reported for P. merguiensis ŽStaples, 1980. and P. indicus ŽParado-Estepa et al., 1987; Kumlu and Jones, 1995. 10 ppt appears to be the lowest critical salinity for penaeid shrimps during nursery stages. In temperate regions, production of penaeid shrimps is limited to a single seasonal crop. To achieve commercial viability, two crops per year or higher average marketable size must be attained during the limited growing season. Intensive shrimp nursery systems operated indoors or in greenhouses may extend the grow-out period by 1–2 months. In such nursery systems, the primary aim is to grow the PLs as dense as possible for 1–2 months with over 70% survival. As shrimps are primarily benthic animals, it may be possible to increase production by increasing the amount of surface area by adding substrates in nursery tanks ŽTidwell et al., 1998.. Studies carried out with the freshwater prawn Mac. rosenbergii have revealed that survival, growth and total yield can be improved in ponds provided with substrates. Cohen et al. Ž1983. reported that additional substrates increased prawn production by 14% and average size by 13%. Similarly, Tidwell et al. Ž1998. found 20% increase in overall production in ponds provided with substrates for the same species. Yet, the present study and those reported elsewhere for marine shrimps have demonstrated that the use of artificial substrates do not produce clear advantages as with the freshwater prawn. Sandifer et al. Ž1987. obtained better survival but not growth with vertical substrates in P. Õannamei. No
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beneficial effects on growth, survival or food conversion rate were also reported for the same species by Samocha et al. Ž1990. and Sturmer et al. Ž1992.. Kumlu and Eroldogan ˘ Ž2000. found similar growth and survival in PLs of P. semisulcatus grown in tanks containing added substrates and the control with no substrates. The current results have also shown that the use of either vertically or horizontally placed substrates, which increased the habitable surface area by about 330%, did not provide any advantage over the control treatment containing no supplemental substrates during the nursery culture of M. monoceros. It may be concluded that since the presence of artificial substrates in tanks does not improve growth and survival and moreover complicates the PL production management, their use is not recommended in nursery culture systems of penaeid shrimps.
Acknowledgements We thank Dr. O. Isik for her support during the culture of micro-algae. This study was financed by the Research Fund ŽSUF 99.4. of the University of C¸ ukurova, Turkey.
References Cawthorne, D.F., Beard, T., Davenport, J., Wickins, J.F., 1983. Responses of juvenile Penaeus monodon Fabricius to natural and artificial sea waters of low salinity. Aquaculture 32, 165–174. Charmantier, G., Charmantier-Daures, M., Bouaricha, N., Thuet, P., Aiken, D.E., Trilles, J.-P., 1988. Ontogeny of osmoregulation and salinity tolerance in two decapod crustaceans: Homarus americanus and Penaeus japonicus. Biol. Bull. Mar. Biol. Lab., Woods Hole, Mass. 175 Ž1., 102–110. Charmantier-Daures, M., Thuet, P., Charmantier, G., Trilles, J.-P., 1988. Salinity tolerance and osmoregulation in post-larvae of Penaeus japonicus and P. chinensis. Effect of temperature. Aquat. Living Resour. 1 Ž4., 267–276. Cohen, D., Ra’anan, Z., Rappaport, U., Arieli, Y., 1983. The production of the freshwater prawn Macrobrachium rosenbergii in Israel. Improved conditions for intensive monoculture. Bamidgeh 35, 31–37. Dall, W., 1981. Osmoregulatory ability and juvenile habitat preference in some penaeid prawns. J. Exp. Mar. Biol. Ecol. 54, 55–64. Dall, W., Hill, B.J., Rothlisberg, P.C., Staples, D.J., 1990. The Biology of the Penaeidae. Advances in Marine Biology, vol. 27. Academic Press. Diwan, A.D., Laximinarayana, A., 1989. Osmoregulatory ability of Penaeus indicus H. Milne Edwards in relation to varying salinities. Proc. Indian Acad. Sci. ŽAnim. Sci.. 98 Ž2., 105–111. Fegan, D.F., 1992. Recent developments and issues in the penaeid shrimp industry. In: Wyban, J.W. ŽEd.., Proceedings of the special Session on shrimp Farming. World Aquaculture Society, pp. 55–70. Harpaz, S., Karplus, I., 1991. Effect of salinity on growth and survival of juvenile Penaeus semisulcatus reared in the laboratory. Isr. J. Aquacult.—Bamidgeh 43 Ž4., 156–163. Kumlu, M., Eroldogan, ˘ O.T., 2000. Effects of temperature and substrate on growth and survival of Penaeus semisulcatus postlarvae. Turk. J. Zool. 24, 337–341. Kumlu, M., Jones, D.A., 1995. Salinity tolerance of hatchery-reared postlarvae of Penaeus indicus H. Milne Edwards originating from India. Aquaculture 130, 287–296. Kumlu, M., Eroldogan, O.T., Aktas, M., 1999a. The effects of salinity on larval growth, survival and ˘ development of Penaeus semisulcatus ŽDecapoda: Penaeidae.. Isr. J. Aquacult.—Bamidgeh 51, 114–121. Kumlu, M., Basusta, N., Avsar, D., Eroldogan, ˘ O.T., 1999b. Some biological aspects of penaeid shrimps in Yumurtalik Bight of North-eastern Mediterranean. Turk. J. Zool. 23, 53–59.
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Kumlu, M., Eroldogan, B., in press. Larval growth, survival and development ˘ O.T., Aktas, M., Saglamtimur, ˘ of Metapenaeus monoceros ŽDecapoda: Penaeidae. cultured in different salinities. Aquacult. Res. Mair, J.McD., 1980. Salinity and water-type preferences of four species of postlarval shrimp Ž Penaeus . from west Mexico. J. Exp. Mar. Biol. Ecol. 45, 69–82. Parado-Estepa, F.D., 1998. Survival of Penaeus monodon postlarvae and juveniles at different salinity and temperature levels. Isr. J. Aquacult.—Bamidgeh 50 Ž4., 174–183. Parado-Estepa, F.D., Ferraris, R.P., Ladja, J.M., De Jesus, E.G., 1987. Responses of intermoult Penaeus indicus to large fluctuations in environmental salinity. Aquaculture 64, 175–184. Potter, I.C., Baronie, F.M., Manning, R.J.G., Lonergan, N.R., 1989. Reproductive biology and growth of the western school prawn, Metapenaeus dalli, in a large western Australian estuary. Aust. J. Mar. Fresh. Res. 40, 327–340. Raj, P.R., Raj, P.J.S., 1982. Effect of salinity on growth and survival of three species of penaeid prawns. Proc. Symp. Coastal Aquacult. 1, 236–243. Ribeiro, A.L.T., Jones, D.A., 1996. Live and artificial diets in feeding Penaeus indicus postlarvae, Book of Abstracts, World Aquaculture ’96, 336 pp. Samocha, T.M., Lawrence, A.L., 1992. Shrimp nursery systems and management. In: Wyban, J. ŽEd.., Proceedings of the Species Session on Shrimp Farming. World Aquaculture Society, Baton Rouge, LA, USA, pp. 87–105. Samocha, T.M., Lawrence, A.L., Biedenbach, J.M., 1990. A new concept for water management strategy for nursery of penaeids postlarvae in raceways. Abstracts, World Aquaculture 90, June 10–14, Halifax, Canada. Sandifer, P.A., Hopkins, J.S., Stokes, A.D., 1987. Intensive culture potential of Penaeus Õannamei. J. World Aquacult. Soc. 18, 94–100. Sokal, P.R., Rholf, F.C., 1981. Biometry. Freeman, San Francisco, 776 pp. Staples, D.J., 1980. Ecology of juvenile and adolescent banana prawns, Penaeus merguiensis in a mangrove estuary and adjacent offshore waters of the Gulf of Carpentaria. I: Immigration and settlement of postlarvae. Aust. J. Mar. Freshwater Res. 31, 635–652. Staples, D.J., Heales, D.S., 1991. Temperature and salinity optima for growth and survival of juvenile banana prawn Penaeus merguiensis. J. Exp. Mar. Biol. Ecol. 154, 251–274. Sturmer, L.N., Samocha, T.M., Lawrence, A.L., 1992. Intensification of penaeid nursery systems. In: Fast, A.W., Lester, L.J. ŽEds.., Marine Shrimp Culture: Principles and Practices. Elsevier, pp. 321–344. Tidwell, J.H., Coyle, S.D., Schulmeister, G., 1998. Effects of added substrate on the production and population characteristics of freshwater prawns Macrobrachium rosenbergii in ponds. J. World Aquacult. Soc. 29, 17–22. Tidwell, J.H., Coyle, S.D., Weibel, C., Evans, J., 1999. Effects and interactions of stocking density and added substrate on production and population structure of freshwater prawns Macrobrachium rosenbergii. J. World Aquacult. Soc. 30, 174–179. Venkataramaiah, A., Lakhsmi, G.J., Gunter, G., 1972. The effects of salinity, temperature and feeding levels on the food conversion, growth and survival rates of the shrimp Penaeus aztecus. Mar. Technol. Soc. Food-Drugs From the Sea Proc., pp. 29–42. Wickins, J.F., 1976. The tolerance of warm-water prawn to recirculated water. Aquaculture 9, 19–37. Zein-Eldin, Z.P., Griffith, G.W., 1969. An appraisal of the effects of salinity and temperature on growth and survival of postlarval penaeids. FAO Fish. Rep. 57 Ž3., 1015–1026.
The effects of salinity and added substrates on growth and survival of Metapenaeus monoceros žDecapoda: Penaeidae/ post-larvae M. Kumlu a,) , O.T. Eroldogan a , B. Saglamtimur b a
Faculty of Fisheries, CukuroÕa UniÕersity, 01330 Balcali, Adana, Turkey b Faculty of Fisheries, Mersin UniÕersity, Mersin, C¸ iftlikkoy, Turkey
Received 28 May 2000; received in revised form 27 October 2000; accepted 10 November 2000
Abstract This study was carried out to determine the optimal culture salinity and to investigate the effects of added substrate on growth and survival of Metapenaeus monoceros during its nursery culture in two separate experiments. In Experiment 1, at the end of a 50-day culture period, post-larvae ŽPLs. reared at 5, 10, 20, 30, 35, 40 and 50 ppt displayed 8, 11, 48, 49, 52, 59 and 36% survivals, respectively. Daily growth rates at salinities above 30 ppt Ž0.266–0.320 mm dayy1 . were about 5-fold higher than those obtained at salinities below 10 ppt Ž0.035–0.056 mm dayy1 . Ž P - 0.05.. Total lengths ŽTL. at 30, 35, 40 and 50 ppt were 19.09, 18.97, 19.09 and 18.89 mm, respectively Ž P ) 0.05.. Mean wet weights acquired at 30–40 ppt Ž63–71 mg. were 7–8 times higher than those at 5 and 10 ppt Ž8.12–9 mg. Ž P - 0.05.. A rise in salinity resulted in a drastic increase in biomass Žover 50-fold. from 0.018 g at 5 ppt to 0.927 g at 40 ppt. Hence, optimum salinity for the nursery culture of M. monoceros PLs appeared to be between 30 and 40 ppt at 288C. In experiment 2, Group A received no additional substrate while the other two groups had added substrates consisting of wooden frame with vertical ŽGroup B. or horizontal ŽGroup C. plastic mesh. Additional substrate increased habitable surface area approximately 330%. Percentage survivals in Group A, B and C were 71, 70 and 63%, respectively. TL was significantly lower in Group C Ž15.65 mm. than in either Group A Ž17.71 mm. or Group B Ž17.23 mm. Ž P - 0.05.. The PLs in Group A attained a significantly greater mean final weight Ž62 mg. than those Ž40–55.14 mg. in both treatments containing artificial substrates. The PLs in Group B and C had
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Corresponding author. Tel.: q90-322-338-6893; fax: q90-322-338-6439. E-mail address: [email protected] ŽM. Kumlu..
0044-8486r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 4 - 8 4 8 6 Ž 0 0 . 0 0 5 8 0 - 9
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12% and 40% lower biomass than that in Group A. The current results demonstrated that the use of either vertically and horizontally placed substrates do not provide any advantage during the nursery culture of M. monoceros. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Metapenaeus monoceros; Post-larvae; Salinity; Substrate; Penaeid; Growth
1. Introduction Salinity is one of the most important abiotic factors influencing the growth and survival of aquatic organisms. Penaeid shrimps are mostly exposed to rapid salinity fluctuations and extreme environmental conditions in estuarine areas during their early life cycle ŽRaj and Raj, 1982.. Hence, in contrast to adults, the post-larvae ŽPLs. and juveniles of most of the species are expected to have a great ability to adapt and osmoregulate well at fluctuating salinities. It is well known that salinity affects food consumption, conversion efficiency and, thus growth, and survival of cultured penaeid shrimps ŽStaples and Heales, 1991.. A considerable number of studies have been conducted to determine effects of salinity alone or in conjunction with other abiotic factors and osmoregulatory ability of commercially important penaeid species such as Penaeus monodon ŽCawthorne et al., 1983; Parado-Estepa, 1998., P. semisulcatus ŽHarpaz and Karplus, 1991; Kumlu et al., 1999a., P. aztecus ŽVenkataramaiah et al., 1972., P. setiferus ŽZein-Eldin and Griffith, 1969., P. Õannamei, P. stylirostris, P. californiensis, P. breÕirostris, ŽMair, 1980., P. merguiensis, P. esculentus, Metapenaeus bennettae ŽDall, 1981., P. japonicus and P. chinensis ŽCharmantier-Daures et al., 1988. and P. indicus ŽKumlu and Jones, 1995.. Studies, with PLs of several shrimp species have revealed that optimal culture salinity is species-specific ŽParado-Estepa et al., 1987; Diwan and Laximinarayana, 1989; Kumlu and Jones, 1995.. Therefore, it is important to determine optimum salinity level for each commercial shrimp species in intensive nursery systems where the salinity can be altered according to optimum requirements of a particular species. Being benthic animals, shrimps are constrained to two-dimensional space rather than three-dimensional volume as with many finfish species. Hence, it may be possible to intensify stocking density by adding artificial substrates into culture tanks to increase habitable surface area for the PLs during nursery culture period. Growth and total yield in the freshwater prawn Macrobrachium rosenbergii were significantly improved by adding substrates in ponds ŽCohen et al., 1983; Tidwell et al., 1998, 1999.. However, artificial habitats constructed of seine netting suspended vertically in raceways improved survival but not growth in the marine shrimp P. Õannamei ŽSandifer et al., 1987.. Studies carried out with other species showed that added substrates did not provide any advantage during the nursery culture of P. Õannamei ŽSamocha and Lawrence, 1992. and P. semisulcatus ŽKumlu and Eroldogan, ˘ 2000.. M. monoceros is an Indo-Pacific species distributed along the coast of Eastern Mediterranean and is one of the most important commercial species in this part of the World. A better understanding for the effects of salinity and added substrates during the nursery culture of this penaeid shrimp species is important in order to define adequate conditions for optimal production.
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Therefore, the primary aims of the present work were to determine optimal culture salinity and to investigate any possible advantage of added substrates on growth and survival of M. monoceros during its nursery stages.
2. Materials and methods The effects of various salinities and two types of added substrates on growth and survival of M. monoceros PLs were investigated in this study. For this purpose, broodstock captured from the Yumurtalik Bight of north-eastern Mediterranean were spawned at the Marine Research Station of the University of Cukurova in Adana, Turkey. 2.1. Experiment 1 Larvae of M. monoceros were fed on micro-algae and Artemia until the PL stages. The PLs were reared on live Artemia nauplii and a granulated diet ŽINVE Aquaculture, Belgium. containing 45% protein until PL10. The animals ŽPL10. previously grown at 40 ppt salinity, were stocked in three replicates for each treatment at a density of 25 PLs into each plastic experimental vessel Ž35 = 20 = 15 cm., supplied with a continuous gentle aeration. The PLs were acclimated to seven different salinities Ž5, 10, 20, 30, 35, 40 and 50 ppt. over a period of 2 days by adding well water or aquarium salt ŽInstant Ocean, Aquarium Systems, USA.. The animals were gradually acclimated to the desired test salinities by reducing or increasing salinity by 2–3 ppt, 7–8 times a day from 40 up to 50 ppt or down to 5 ppt. Rearing water was filtered to 1 mm with a sand filter and a series of cartridge filters Ž10, 5 and 1 mm.. All the animals were kept in the final test salinities for at least 8 days before the first sampling carried out on the 10th day of the experiment. The PLs were fed the granulated feed four times daily to excess. Salinity and temperature measurements were performed with a direct reading digital salinometer ŽYSI, USA.. The pH was measured weekly with a digital pH meter ŽWTW, Germany.. Ammonia levels were not measured in the present study. However, in a previous penaeid study, in the same system, at highest loading, the maximum level of total ammonia was 0.175 mg ly1 , which is within the acceptable range for penaeids ŽWickins, 1976.. The experiment, which lasted 50 days, was conducted under a controlled photoperiod Ž10 Lr12 D. with artificial fluorescent illumination and the water temperature was maintained at 288C. Uneaten food was removed daily when 25–50% of the rearing water was renewed. A complete water exchange was performed every 10 days, and simultaneously the PLs were counted and 10–12 of them were measured from the tip of the rostrum to the end of the tail using calipers Ž"0.01 mm.. The PLs were rolled in tissue paper to remove surface moisture prior to weighing. At the end of the experiment the animals at PL60 were weighed on a scale Ž"0.001 g. to determine individual wet weight and total biomass.
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2.2. Experiment 2 This experiment was conducted to investigate any possible advantage of two types of artificial substrates on growth and survival of M. monoceros PLs. For this, the animals ŽPL20. were stocked at a density of 120 individuals into each aquarium Ž30 = 20 = 22 cm. in three replicates for each treatment. The treatment used in the experiment were as follows: Group A Žcontrol. with no artificial substrate, Group B with vertically placed artificial substrate and Group C with horizontally suspended substrate. The surface habitable area, which was 600 cm2 in the control group, was increased to about 2000 cm2 in Groups B and C. The substrates were constructed of wooden squares Ž15 = 15 cm. covered with a course mesh Ž0.5 mm. and placed in the form of a three layer-rack where each layer was 7 cm apart from each other ŽGroup B. or suspended from top of each aquarium in again three layer being 7 cm apart ŽGroup C.. Throughout the 30-day culture period Ž30 days., the PLs were fed the same granulated diet to excess as in the first experiment four times daily. Each day, 100% water exchange was carried out. Water pH and temperature were 8.0–8.1 and 288C, respectively. Animals inhabiting the artificial substrates in Groups B and C were counted everyday at 1000 to 1100 h. At the end of the experiment, all the animals in each treatment were counted and measured for their TL and weight as described in the first experiment. 2.2.1. Statistical analysis Data were analysed using one-way ANOVA and any significant difference was determined at 0.05 probability level by Scheffe’s test after the normality and homogeneity ŽBartlett’s test. of the data were checked ŽSokal and Rholf, 1981. in Minitab statistical software.
3. Results 3.1. Experiment 1 Following a gradual acclimatisation over a period of 48 h, the percentage survivors in 5 or 10 ppt were over 80% on the 3rd day of the experiment. Post-larval mortality in each test salinity was high during the first 20 days of the culture. Yet, although survival was levelled off at salinities above 20 ppt, mortality remained high at 5 and 10 ppt throughout the experiment ŽFig. 1.. Figs. 1 and 2 show that M. monoceros PLs had higher survival and better growth at high rather than low salinities between PL10 and PL60. The lowest salinities Ž5 and 10 ppt. consistently produced high mortalities throughout the experiment resulting in only 8–11% final survivals ŽFig. 1, Table 1.. The highest salinity level Ž50 ppt. tested in this study resulted in only 36% survival as compared to 49% at 30 ppt, 52% at 35 ppt and 59% at 40% ppt. Final survival at 40 ppt Ž59%. was significantly higher than at all other salinities Ž P - 0.05. ŽFig. 1, Table 1.. Growths as TL at salinities below 20 ppt were also significantly lower than those sustained at higher salinity levels Ž P - 0.05. ŽFig. 2..
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Fig. 1. Survival of M. monoceros PLs grown at various salinities from PL10 to PL60. Each symbol is a mean Ž ns 3..
The PLs grown at 5 and 10 ppt displayed growth rates between 0.035 and 0.056 mm dayy1 between PL10 and PL60 as compared to 0.153–0.320 mm dayy1 at higher salinities ŽTable 1.. Final TL at 5 and 10 ppt were 11.5 and 7.18 mm, respectively Ž P ) 0.05.. Growth rates of PLs, which ranged between 0.264 and 0.320 dayy1 , at 30, 35, 40 and 50 ppt were not significantly different from each other Ž P ) 0.05. ŽTable 1.. Total lengths at 30, 35, 40 and 50 ppt were 19.09, 18.97, 19.09 and 18.89 mm, respectively Ž P ) 0.05.. The PLs reared at 20 ppt had an intermediate growth Ž15.07 mm TL and a growth rate of 0.153 mm dayy1 . between high Ž30–50 ppt. and low salinities Ž5–10 ppt.. Daily growth rates obtained at salinities above 30 ppt were about 5-fold higher than those obtained at salinities below 20 ppt. These results show that salinities below 20 ppt slow the growth and produce high mortality during nursery culture of M. monoceros. Optimum culture salinity for the PLs appeared to be between 30 and 40 ppt at 288C. The results of individual wet weight and total biomass also confirmed the above findings. PLs grown at 5 and 10 ppt attained the lowest individual wet weight Ž8.12–9 mg. while those at 30 ppt had the highest mean weight Ž70.54 mg. at the end of the
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Fig. 2. Total length Žmm. of M. monoceros PLs grown at various salinities from PL10 to PL60. Each symbol is a mean Ž ns 3..
50-day culture period Ž P - 0.05. ŽFig. 3, Table 1.. The results showed that mean weight obtained at 30 ppt was 7–8 times higher than that at 5 or 10 ppt. At PL60, final mean weights of PLs reared at 30, 35 and 40 ppt were not significantly different from each other Ž P ) 0.05.. PLs at 50 and 20 ppt had lower mean weights than those at 30–40 ppt Ž P - 0.05.. Table 1 and Fig. 3 show that, at PL60, the PLs cultured at 30, 35 and 40 ppt exhibited the greatest biomass ranging from 0.853 to 0.927 g. The lowest biomass were obtained at 5 Ž0.018 g. and 10 ppt Ž0.031 g.. A rise in salinity resulted in a drastic increase in biomass from 0.018 g at 5 ppt to 0.927 g at 40 ppt. The increase in biomass between 5 and 40 ppt was 51.5-fold. Yet, the biomass showed a 50% decline at 50 ppt as compared to that resulted at 40 ppt ŽTable 1.. Throughout the experiment, temperature and pH of the water in culture vessels were 27.8–28.28C and 7.95–8.13, respectively. 3.2. Experiment 2 The mean daily number of PLs inhabiting the two different substrates was 24 in Group B and 14 in Group C. Hence, it appeared that the vertical substrate was
Salinity
Final survival Ž%. Final TL Žmm. Growth rate Žmm dayy1 . Mean weight Žmg. Biomass Žg.
5 ppt
10 ppt
20 ppt
30 ppt
35 ppt
40 ppt
50 ppt
8.00"3.15d
10.67"2.52 d
48.00"1.00 b
49.30"4.16 b
52.00"2.00 b
58.67"3.06 a
36.00"2.00 c
11.5"2.98 d
7.18"2.25 c
15.07"3.51b
19.09"6.28 a
18.97"3.10 a
19.09"4.16 a
18.89"2.45a
0.056
0.035
0.153
0.320
0.272
0.266
0.264
9.00"3.56
8.12"2.25
37.51"4.72
70.54"8.14
65.50"4.86
63.18"7.70
56.22"3.49
0.018"0.04
0.031"0.07
0.440"0.06
0.870"0.12
0.853"0.09
0.927"0.13
0.506"0.14
Each value is a mean"S.D. Values marked with different superscripts in each row are significantly different from each other Ž P - 0.05..
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Table 1 Final survival, total length, mean individual weight and biomass of M. monoceros PLs grown for 50 days at various salinities
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Fig. 3. Mean wet weight Žsolid bars. and biomass Žhatched bars. of M. monoceros at PL60 reared at various salinities from PL10 to PL60. Each bar represents a mean"S.D. Ž ns 3 for each test salinity.. Treatments marked with different superscripts are significantly different from each other Ž P - 0.05..
unexpectedly preferred by the PLs. Final survivals in Groups A, B and C were 71%, 70% and 63%, respectively. Table 2 shows that growth as TL was significantly lower in Group C Ž15.65 mm. than in either Group A Ž17.71 mm. or Group B Ž17.23 mm. Ž P - 0.05.. The PLs in the control treatment ŽGroup A. attained a significantly greater mean final weight than those Ž40–55.14 mg. in both treatments containing artificial habitats ŽTable 2.. Horizontal substrate ŽGroup C. resulted in the lowest post-larval TL, weight and biomass Ž P ) 0.05.. The PLs in Group B and C had 12% and 40% lower biomass than that in the control ŽGroup A..
Table 2 Final survival, total length, weight and biomass of M. monoceros reared in various treatments for 30 days Treatments Group A Group B Group C
Survival Ž%. 71.25 70 62.5
Total length Žmm. a
17.71"5.49 17.23"4.46 a 15.65"4.82 b
Weight Žmg. a
62.13"6.91 55.14"8.65 b 40.00"3.65 c
Biomass Žg. 10.19 8.93 6.12
Each value for total length and weight is a mean"S.D. Values in each column marked with different superscripts are significantly different from each other Ž P - 0.05.. ŽGroup A: control without substrate, Group B: with vertical substrate, Group C: with horizontal substrate..
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All these results showed that the use of either vertically or horizontally placed substrates did not provide any advantage over the control treatment during the nursery culture of M. monoceros. In fact, the artificial substrates used in the present study had negative impacts on post-larval survival and growth. 4. Discussion A gradual acclimation over a period of 48 h has been suggested to be adequate for the PLs of P. indicus ŽParado-Estepa et al., 1987; Kumlu and Jones, 1995. and P. monodon ŽCawthorne et al., 1983.. In the current work, this acclimation rate resulted in poor survivals in M. monoceros PLs reared particularly at 5 and 10 ppt salinities during the first 10-day culture period. One may argue that the PLs might have needed a slower acclimation rate than that applied in the first experiment. However, considerably high mortalities observed at all the experimental test salinities including the normal sea water salinity Ž40 ppt. indicated that some other reasons might have contributed to high post-acclimation mortality encountered in this study. The PLs acclimated to 20 and 30 ppt had the highest survivals on the 10th day of the culture. It is known that considerable losses may occur in penaeid shrimps during early nursing culture when the PLs are forced to shift from natural diet to artificial diet ŽFegan, 1992; Ribeiro and Jones, 1996.. It is thought that this might be the main reason why high PL mortality was obtained during the acclimation process. The survival curves showed a normal pattern only after the 20th day of the culture ŽFig. 1.. Most penaeid shrimps are known to be euryhaline species growing in a wide range of salinities at least during their nursery stages. Kumlu et al. Žin press. found that the larvae of M. monoceros from broodstock originating from eastern Mediterranean are good osmoregulators in high salinities rather than low salinities and that the lowest critical salinity was 22 ppt despite an acclimation rate of 4–5 ppt hy1 . Yet, the present results indicate that this shrimp species could neither tolerate low nor high salinities well during the PL stages. Between PL10 and PL60, the animals reared at 5–10 ppt and 50 ppt showed 90% and 65% mortality, respectively, during the 50-day culture period indicating that the PLs of this species were not successful to withstand such extreme salinities. It appears that, to some extent, M. monoceros larvae acquired an ability during the early PL stages to survive in salinities lower than 20 ppt conforming with general life cycle of penaeid shrimps. This agrees with the findings of Charmantier et al. Ž1988. who stated that salinity tolerance of P. japonicus decreased through the larval stages, was at a minimum at metamorphosis, but increased in post-larval stages. An increase in salinity from 5–10 to 40 ppt resulted in a consistent rise in survival, total length and biomass. Despite the fact that P. semisulcatus and M. stebbingi were abundant in estuarine areas in the north-eastern Mediterranean, M. monoceros has never been caught in these areas ŽKumlu et al., 1999b.. These authors captured the specimens of this penaeid shrimp always at depths above 20 m and at normal marine salinities Ž39–40 ppt.. Hence, it appears that unlike other Metapenaeus species, which complete their life cycle ŽDall et al., 1990. or even spawn in estuarine waters of - 10 ppt ŽPotter et al., 1989., M. monoceros from the north-eastern Mediterranean prefers higher saline media even during its nursery stages.
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The present results and studies elsewhere have shown that euryhalinity and optimal salinity resulting in best growth and survival in shrimps differ by species and post-larval stages. Kumlu and Jones Ž1995., and Raj and Raj Ž1982. reported good growth and survival in hatchery-reared or wild-caught P. indicus post-larvae at even 5 ppt salinity. However, the former found that euryhalinity to low salinity of 10 ppt was gradually lost after PL40 and concluded that 25 ppt was optimal for P. indicus during nursery stages. In the current work, between PL10 and PL60, the animals had consistently better survival, greater total length and weight gain between 30 and 40 ppt than at either high Ž50 ppt. or low Ž5–20 ppt. salinities indicating that their optimal culture salinity is in this range. Salinity optima for the larval culture of the same species inhabiting the north-eastern Mediterranean were also reported to be 40 ppt ŽKumlu et al., in press.. Growth rates of M. monoceros PLs at salinities above 30 ppt were significantly higher than the lower salinities Ž5–20 ppt.. Mean wet weights at salinities above 30 ppt were 7–8 times higher than those at 5–10 ppt. Again, biomass attained at 40 ppt was 52-fold greater than that at 5 ppt. It is generally accepted that penaeid PLs grow well in low saline environments and that this low salinity preference might be a useful adaptation to their natural nursery habitats ŽDall, 1981.. Unlike other penaeid species, M. monoceros were not able to adapt themselves to low salinities even at early PL stages ŽPL10-20. indicating that this species is rather stenohaline during PL stages. The PLs consistently showed poor survival at salinities lower than 20 ppt throughout the first experiment. In fact, post-larval growth rate Ž0.32 mm dayy1 . was 5–9 times higher than those at 5 ppt or 10 ppt throughout the experiment. These results indicate that the PLs of this species do not grow and survive well at salinities above 50 or below 10 ppt. Hence, this penaeid shrimp does not seem to be a good candidate for culturing in brackish water environments. For M. monoceros PLs, the lowest and highest critical salinities appeared to be 10 and 50 ppt, respectively. Based on the present results and those reported for P. merguiensis ŽStaples, 1980. and P. indicus ŽParado-Estepa et al., 1987; Kumlu and Jones, 1995. 10 ppt appears to be the lowest critical salinity for penaeid shrimps during nursery stages. In temperate regions, production of penaeid shrimps is limited to a single seasonal crop. To achieve commercial viability, two crops per year or higher average marketable size must be attained during the limited growing season. Intensive shrimp nursery systems operated indoors or in greenhouses may extend the grow-out period by 1–2 months. In such nursery systems, the primary aim is to grow the PLs as dense as possible for 1–2 months with over 70% survival. As shrimps are primarily benthic animals, it may be possible to increase production by increasing the amount of surface area by adding substrates in nursery tanks ŽTidwell et al., 1998.. Studies carried out with the freshwater prawn Mac. rosenbergii have revealed that survival, growth and total yield can be improved in ponds provided with substrates. Cohen et al. Ž1983. reported that additional substrates increased prawn production by 14% and average size by 13%. Similarly, Tidwell et al. Ž1998. found 20% increase in overall production in ponds provided with substrates for the same species. Yet, the present study and those reported elsewhere for marine shrimps have demonstrated that the use of artificial substrates do not produce clear advantages as with the freshwater prawn. Sandifer et al. Ž1987. obtained better survival but not growth with vertical substrates in P. Õannamei. No
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beneficial effects on growth, survival or food conversion rate were also reported for the same species by Samocha et al. Ž1990. and Sturmer et al. Ž1992.. Kumlu and Eroldogan ˘ Ž2000. found similar growth and survival in PLs of P. semisulcatus grown in tanks containing added substrates and the control with no substrates. The current results have also shown that the use of either vertically or horizontally placed substrates, which increased the habitable surface area by about 330%, did not provide any advantage over the control treatment containing no supplemental substrates during the nursery culture of M. monoceros. It may be concluded that since the presence of artificial substrates in tanks does not improve growth and survival and moreover complicates the PL production management, their use is not recommended in nursery culture systems of penaeid shrimps.
Acknowledgements We thank Dr. O. Isik for her support during the culture of micro-algae. This study was financed by the Research Fund ŽSUF 99.4. of the University of C¸ ukurova, Turkey.
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