- Email: [email protected]
The influence of salinity, diurnal rhythm and daylength on feeding behavior in Meretrix meretrix Linnaeus
Aquaculture 252 (2006) 584 – 590 www.elsevier.com/locate/aqua-online
The influence of salinity, diurnal rhythm and daylength on feeding behavior in Meretrix meretrix Linnaeus Shuhong Zhuang * Biological Science and Chemical Engineering School, Yantai University, Yantai 264005, China Received 27 September 2004; received in revised form 20 June 2005; accepted 21 July 2005
Abstract A nature-simulating culture system was used to explore the influence of salinity, the diurnal cycle and daylength on ingestion rate (IR) and assimilation efficiency (AE) of Meretrix meretrix. The clams used in the experiments were grouped into three sizes: small, with a shell length of 2.70 F 0.10 cm and a dry fresh weight of 0.35 F 0.04 g; medium, with a shell length of 4.00 F 0.05 cm and a dry fresh weight of 1.25 F 0.05 g; and large, with a shell length of 5.00 F 0.10 cm and a dry fresh weight of 2.45 F 0.10 g. The clams in all size groups demonstrated a common response pattern in IR and AE under salinities ranging from 18 to 34 ppt. The clams achieved the greatest IR within the salinity range 27 to 30 ppt. There was a marked reduction in IR outside this range. Of the salinities tested 18 ppt was the harshest stress to the feeding of M. meretrix. Between the salinities 24 to 34 ppt, changes in AE of the clam were the inverse of those observed in IR, suggesting that M. meretrix is able to compensate for the loss of IR by an increase in AE. Although the effect of both salinity and body size of the clam was significant on both IR and AE, salinity had evidently stronger influence than body size. All sizes of clam showed a three-phase diurnal feeding pattern: a high ingestion phase from 00:00 to 08:00, a low ingestion phase from 12:00 to 20:00, and a changing phase between low and high ingestion phases. The IR response to daylength comprised a high and constant feeding phase at daylengths from 0 to 16 h (longer darkness) and a declining and unstable feeding phase as daylength increased from 16 to 24 h (shorter darkness). All sizes of clams demonstrated an inverse adaptation to AE compared with IR, indicating that the clam is able to achieve a stable feeding physiology by compensating for daylength-induced variations in IR by changing AE. The ANOVA analysis also showed that both diurnal cycle and daylength affected IR and AE of the clam very significantly, body size did not, however. D 2005 Elsevier B.V. All rights reserved. Keywords: Meretrix meretrix; Ingestion rate; Assimilation efficiency; Salinity; Diurnal cycle; Daylength
1. Introduction
* Fax: +86 535 6902063. E-mail addresses: [email protected], [email protected]. 0044-8486/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2005.07.036
Meretrix meretrix L. is a nearly equilateral, triangular shaped clam with highly coloured shells. It inhabits sandy substrates in the lower intertidal and shallow subtidal areas of the Bohai and western Yel-
S. Zhuang / Aquaculture 252 (2006) 584–590
low Seas. For several years this clam has been cultured by the native farmers of the Shandong Peninsula, China because of its relatively high meat yield, delicious and tender taste and ease of culture in the natural habitat as well as for its attractive appearance (He et al., 1997; Zhuang and Wang, 2004). The feeding physiology and ecology of bivalves, particularly cultured species, have been widely studied for decades. In these studies, physiological and ecological parameters, such as clearance rate, ingestion rate, assimilation efficiency and scope for growth, have been widely used in considering the energetic budget and nutrient cycles (Aldridge et al., 1995; Fang et al., 1996; Kuang et al., 1996; MacDonald et al., 1998; Hawkins et al., 2002). In a previous study, the feeding physiology of M. meretrix on a laboratory scale was preliminary to a further determination of economical farming densities and environmental carrying capacity in the local intertidal zones and shallow sub-littoral areas (Zhuang et al., 2004). In order to highlight feeding behavior under different culture circumstance, this subsequent study was focused particularly on the variation of ingestion rate and assimilation efficiency as influenced by salinity, diurnal cycle and daylength. There is currently no information on these aspects of the physiology of this species in the scientific literature.
2. Materials and methods 2.1. Clams used in the experiments A range of sizes of M. meretrix to support the experiments was collected from the intertidal zone of the local island of Changshan archipelago in July 2003. The collected clams were grouped into 3 sizes: small, with a shell length of 2.70 F 0.10 cm and a dry fresh weight of 0.35 F 0.04 g; medium, with a shell length of 4.00 F 0.05 cm and a dry fresh weight of 1.25 F 0.05 g; and large, with a shell length of 5.00 F 0.10 cm and a dry fresh weight of 2.45 F 0.10 g. The healthy clams were acclimated for at least one week in a acclimation tank of the laboratory culture system to an ambient temperature of 16–18 8C and a natural diurnal cycle of 13 h light / 11 h dark. After acclimation healthy individuals were selected for each experiment. During the acclimation the diet type and
585
concentration in the culture tanks were identical to those used in the experiments. 2.2. Experimental methods The experiments were carried out in the marine propagation center of the Changdao Institute of Marine Aquaculture between August and October 2003. A tank culture system was set up to simulate the natural environment of the clam with regard to both water and substrate. Seawater was first pumped into a large (100 m3) sedimentation container and then into a smaller reservoir. The latter functioned as a water pressure regulator and an inflow diet concentration regulator to maintain a constant flow of water with constant diet concentration into the 40 40 45 cm deep culture tanks in which the clams were held. The clams were stocked at a density of 10 per tank. Each experiment comprised four replicate culture tanks and two controls that were used to eliminate the influence of both diet propagation (such as microalgae) and sedimentation as experimental variables. During the experiments the diet concentration in the inflow and outflow water was microscopically monitored. The diet concentration of inflow water was regulated by adding the microalga, Isochrysis zhanjangensis, to the reservoir tank. For each experiment the shell length and dry weight of both the shell and the flesh of the clam were precisely measured. To determine the effect of salinity, the feeding pattern of the clam was observed for three days at each of the following five salinities: 18, 23, 27, 30 and 34 ppt (NaCl) which were diluted with fresh water or strengthened with sea salt. The treatment of salinities was separate with the test sequence from 18 to 34 ppt. After a salinity treatment had been finished, the salinity in the reservoir was regulated for next salinity treatment and the clam in the culture tank was renewed from the acclimation tank. The salinity of the culture water was measured with a salinometer (Jenco-3107). For observation of the feeding rhythm of the clam during the diurnal cycle, a normal cycle of 12 h light (06:00 to 18:00 h) / 12 h dark (18:00 to 06:00 h) was chosen to obtain a generalized and unstressed feeding pattern. The light intensity used in the light period was 9.8 W m 2 (on the water surface of the culture tank) which was about the average light intensity at the
586
S. Zhuang / Aquaculture 252 (2006) 584–590
local coast (Yantai Ocean and Fishery Bureau, 2002). This light intensity was also used to determine the effect of various daylengths (0, 4, 8, 12, 16, 20 and 24 h light) on feeding. The treatments of different daylengths used in the experiment were 0 h light / 24 h dark, 4 h light / 20 h dark, 8 h light / 16 h dark, 12 h light / 12 h dark, 16 h light / 8 h dark, 20 h light / 4 h dark, and 24 h light / 0 h dark, respectively. In the experiment the clam was observed for three days. The data used in the study was a mean of measured data in each three-day experiment. All treatments were done separately and in all experiments water samples were taken every 4 h for the measurement of feeding activities of the clams. In the dark period, samples were taken with a dim red light that avoided imposing light stress on the feeding of the clam. In and around the culture room man-made sounds and disturbances were minimized during the observation periods. The experiments were carried out at ambient water temperatures (i.e. 16–18 8C). The diet concentration (microalga) was maintained at 0.7–0.9 106 cells L 1 and the flow velocity of the seawater from the smaller reservoir container to the culture tank at 80–100 L min 1. This provided the
standard against which the experimental deviation of ingestion rate and assimilation efficiency of M. meretrix was measured. During the experiment there was no pseudofaeces produced by the clam. After each treatment with salinity and daylength in the experiments, a sub-sample of faecal material was collected from 6 chambers containing a clam under the same treatment conditions using a pipette and without disturbing the feeding clams. The faecal sample was concentrated onto pre-weighted Whatman GF/C filters for dry weight and ash-free dry weight determination (Gardner, 2000). The diet concentration was indicated by the content of total particulate matter (TPM) and particulate organic matter (POM) in the seawater of the culture tank. TPM and POM were determined following the procedures described by Bayne and Newell (1983), Sun et al. (1995) and Dong et al. (2000). A sample of water (1000 ml) was first vacuum filtered through marked GF/C Whatman glass–fiber filters (mesh 1.2 Am) which had been burned at 450 8C for 6 h before weighing (W 0). The filtered material was rinsed with 0.5 mol L 1 NH4COOH to get rid of the salts before being dried at 110 8C for 12 h and weighed to get the
1.6
IR (mg g-1 h-1)
1.4 1.2 1.0 0.8
Small (Mean ± SD) Medium (Mean ± SD) Large (Mean ± SD)
0.6 0.4 0.2 18
23
27
30
34
Salinity (ppt) 80
AE (%)
70 60 50 40 18
23
27
30
34
Salinity (ppt) Fig. 1. The effect of salinity on ingestion rate (IR) and assimilation efficiency (AR) of three size groups of Meretrix meretrix.
S. Zhuang / Aquaculture 252 (2006) 584–590 Table 1 ANOVA testing for the effects of salinity and body size upon IR and AE of Meretrix meretrix Item
Source
df
SS
IR
Salinity Body size Error Total Salinity Body size Error Total
4 2 8 14 4 2 8 14
2.5693 0.0973 0.0627 2.7293 836.9693 11.8813 41.5387 890.3893
AE
MS
F
P
0.6423 0.0487 0.0078
82.00 6.21
0.0000** 0.0235*
209.2423 5.9407 5.1923
40.30 1.14
0.0001** 0.3656
first dry weight (W 110). This was re-weighed after burning at 450 8C for 6 h to give the second dry weight (W 450). Finally, TPM and POM were calculated as following respectively, TPM ¼ W110 W0 ;
POM ¼ W110 W450 :
587
the experiment; Ceo and Cet the diet concentration in the inflow and outflow water of the culture tank respectively (mg L 1); t the duration of the experiment; Sed refers to the coefficient of variation in the diet concentration of controls; Cco and Cct the diet concentration in the inflow and outflow water of the culture tank in the control, respectively (mg L 1). 2.3.2. Assimilation efficiency Assimilation efficiency (AE %) was determined following Conover (1966): AE ¼ 100 ð FV EVÞ=½ð1 EVÞ FV where FV refers to the percentage of assimilated diet weight minus ash in the total assimilated diet weight; EVthe percentage of faeces (dry weight) minus ash in the total excreted faeces.
2.3. Computing methods
3. Results
2.3.1. Ingestion rate Ingestion rate (IR, mg g 1 h 1) was calculated as follows (Jorgensen, 1943; Zhuang et al., 2004; Zhuang and Wang, 2004):
3.1. Salinity influences on IR and AE
IR ¼ V ½Ceo ðCeo SedÞ Cet=ð M t Þ Sed ¼ ðCco CctÞ=Cco where V refers to the volume of the culture tank (L); M the dry weight of the soft part of the clams used in
The results show that the IR of all sizes of clam was highest at salinities of 27–30 ppt and decreased either side of this range (Fig. 1). And AE for all sizes of the clam was lowest at 18 ppt, reaching its highest value at 23 ppt. Over this salinity AE decreased, remained relatively constant from 27 to 30 ppt and then slightly increased. Based on these responses of
1.5
IR (mg g-1 h-1)
1.2 0.9 0.6 Small (Mean± SD) Medium (Mean± SD) Large (Mean± SD)
0.3 0.0 12:00 Light
16:00 Light
20:00 Dark
0:00 Dark
04:00 Dark
08:00 Light
Time Fig. 2. The diurnal pattern of ingestion rate of three size groups of Meretrix meretrix exposed to a 12 h light (06:00 to 18:00 h) / 12 h dark (18:00 to 06:00 h) cycle.
588
S. Zhuang / Aquaculture 252 (2006) 584–590
Table 2 ANOVA testing for the effects of feeding time upon IR of Meretrix meretrix Item
Source
df
SS
MS
F
P
IR
Feeding time Body size Error Total
5 2 10 17
1.0593 0.0088 0.0224 1.0905
0.2119 0.0044 0.0022
94.77 1.98
0.0000** 0.1889
IR and AE, a salinity of 18 ppt appears to be a relatively harsh stress with regard to the feeding physiology of the clam. It is statistically (ANOVA) shown that both size-related and salinity-related differences in IR and AE of the clam were significantly different, respectively P b 0.05 and P b 0.001, however, the salinity had more influence than body size of the clam on IR and AE (Table 1). 3.2. Feeding rhythm during a diurnal cycle
IR (mg g-1 h-1)
The feeding pattern, as indicated by IR, during a 12 h light / 12 h dark diurnal cycle was similar for all
sizes of clams (Fig. 2). It had three phases: a high ingestion phase from 00:00 to 08:00 h, a low ingestion phase from 12:00 to 20:00 h, and a changing phase between 20:00 and 00:00 h in which there was a sharp increase in IR from the low to the high feeding phase. For all clams the highest IR was observed at 00:00 h. In this normal diurnal cycle the clams with different sizes showed no difference in IR, but significant differences were found between different feeding times for all three sizes of clams (Table 2.). The feeding time exerted more influence on IR than the body size of the clam. 3.3. Impact of daylength on IR and AE The relationship between food ingestion (as indicated by IR) and daylength could be divided into two types: a high and constant level of feeding at daylengths from 0 (total dark) to 16 h, and a declining and less stable level of feeding with further increases in daylength from 16 to 24 h (total light) (Fig. 3). However, small clams did not conform to this pattern, the
1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0
4
8
12
16
20
24
Day length (h) 75
AE (%)
70 65 60 Small (Mean± SD) Medium (Mean± SD) (Mean± SD) Large
55 50 0
4
8
12
16
20
24
Day length (h) Fig. 3. The effect of daylength on ingestion rate (IR) and assimilation efficiency (AE) of three size groups of Meretrix meretrix.
S. Zhuang / Aquaculture 252 (2006) 584–590 Table 3 ANOVA testing for the effects of daylength and body size upon IR and AE of Meretrix meretrix Item
Source
df
SS
IR
Daylength Body size Error Total Daylength Body size Error Total
6 2 12 20 6 2 12 20
0.7038 0.0028 0.0192 0.7257 324.0057 0.0152 26.4314 350.4524
AE
MS
F
P
0.1173 0.0014 0.0016
73.49 0.87
0.0000** 0.4433
54.0010 0.0076 2.2026
24.52 0.00
0.0001** 0.9965
decline in their IR being continuous throughout the whole range of daylengths. It should be noted that the IR of small clams at daylengths less than 12 h was higher than that of the larger clams, but lower at daylengths above 12 h. Regarding to changes in AE with increasing daylength, all sizes of clams displayed a contrary pattern to that shown for IR, i.e. AE increased continuously with increasing daylength (Fig. 3). Similarly, the influence of body size on both IR and AE was insignificant, but that of daylength was very significant ( P b 0.001) (Table 3).
4. Discussion Like most marine bivalves, salinity is one of the most important factors influencing the feeding of M. meretrix. In agreement with the study on feeding activity of Chilean scallop (27–30 ppt) by Navarro and Gonzalez (1998), Perna viridis (optimum range: 26–30 ppt) by Yang et al. (2000) and Manila clam (optimum range: 25–30 ppt) by Wu et al. (2002), the optimum salinity for IR of M. meretrix was found to be similar in the range between 27 and 30 ppt which is consistent with the study made by Lin and Xu on the same species (Lin and Xu, 1997). It is found that the place most inhabited by this clam in the local intertidal zone is far from the estuary where the salinity is relatively low and fluctuates greatly (Lin and Xu, 1997). This range of salinity tolerance and the optimum salinity for growth of M. meretrix will be very helpful and instructive for the local farmers who live around the Bohai Gulf to which many rivers lead, resulting in a large range in salinity (24–30 ppt) near the estuaries (Yantai Ocean and Fishery Bureau, 2002). Our data will facilitate the selection of optimal
589
intertidal areas to cultivate this clam. The phenomenon observed in the experiment that the response to AE of the clam was the converse of that shown to IR within a certain range of salinity (23–34 ppt), suggests that ingestion, assimilation and metabolism would be closely related and coordinated in the feeding physiology of M. meretrix. This supports the contention that the clam could compensate to a certain extent for a reduction in ingestion rate, through severe salinity or other environmental impacts, with higher levels of assimilation efficiency and even metabolic levels (Beiras et al., 1995; Navarro and Gonzalez, 1998; Bayne and Newell, 1983; Wu et al., 2002). The feeding rhythm of M. meretrix under the diurnal cycle 12 h light / 12 h dark used in this study coincides well with that of Manila clam Ruditapes philippinarum as described by Wu et al. (2002). They suggested that bivalves living within a similar habitat and experiencing similar environmental influences would have a similar feeding rhythm. The distinct three phases of the feeding rhythm of all sizes of the clam clearly suggest that this feeding rhythm would be mainly attributed to the light/dark cycle which could affect the movement and availability of their food (Yamamuro et al., 2000; Wong and Chueng, 2001; Wu et al., 2002). Although it is not possible to determine the smallest size at which the clam demonstrates this biological feeding rhythm, this study shows that M. meretrix larger than 2.70 cm in size has the same day/night feeding rhythm. As in other bivalves, the biological feeding rhythm of M. meretrix is the result of long-term co-influences of diet availability, light, temperature and tidal movement on the clam. This inherent feeding rhythm of bivalves is demonstrable even if the variable factors are absent (Yang et al., 2000; Wu et al., 2002). Since the feeding of activity of M. meretrix shows a marked nocturnal form the species is able to achieve a higher feeding level in a shorter day and a lower one in a longer day. The approximately inverse responses of IR and AE to an increase in daylength demonstrate again that the clam compensates for a reduction in IR by an increased AE, on this occasion under the influence of changing daylengths. As to the inverse response of the clam in IR and AE, there is a number of ways that bivalves can respond to food availability (Ward and Shumway, 2004). Prior-ingestive selection outside the stomach
590
S. Zhuang / Aquaculture 252 (2006) 584–590
and post-ingestive selection in the stomach (Brillant and MacDonald, 2000) which enable the bivalve in nature to have a different gut retention time for organic and inorganic particles could help the animals balance IR and AE for maintaining an optimal physiological metabolism. Also by adjusting feeding rates and enzymatic activities, AE in bivalves was able to remain constant, irrespective of the changes in food availability (Wong and Cheung, 2001).
Acknowledgements The author is very grateful to the technical cooperation with the Changdao Department of Marine and Aquatic Production for their assistance and support in building the culture system and to Dr. Neil Bourne, Pacific Biological Station, Nanaimo, for revising the MS.
References Aldridge, D.W., Payne, B.S., Miller, A.C., 1995. Oxygen consumption, nitrogenous excretion and filtration rates of Dreissena polymorpha at temperatures between 20–32 8C. Can. J. Fish. Aquat. Sci. 52, 761 – 767. Bayne, B.L., Newell, R.C., 1983. Physiological energetics of marine molluscs. In: Saleuddin, A.S.M., Wilbur, K.M. (Eds.), The Mollusca, Vol.4. Physiology, Part I. Academic Press, New York, pp. 407 – 515. Beiras, R., Camacho, A.P., Albentosa, M., 1995. Short-term and long-term alteration in the energy budget of young oyster Ostrea edulis L. in response to temperature change. J. Exp. Mar. Biol. Ecol. 186, 221 – 236. Brillant, M.G.S., MacDonald, B.A., 2000. Postingestive selection in the sea scallop, Placopecten magellanicus (Gmelin): the role of particle size and density. J. Exp. Mar. Biol. Ecol. 253, 211 – 227. Conover, R.J., 1966. Assimilation of organic matter by zooplankton. Limnol. Oceanogr. 22, 338 – 354. Dong, B., Xue, Q.Z., Li, J., 2000. Environmental factors affecting the feeding physiological ecology of Manila clam, Ruditapes philippinarum. Oceanol. Limnol. Sinica 31, 636 – 642. Fang, J.G., Kuang, S.H., Sun, H.L., Li, F., 1996. Study on the carrying capacity of Sanggou Bay for the culture of scallop Chlamys farreri. Chin. J. Mar. Fish. Res. 17, 18 – 31. Gardner, J.P.A., 2000. Where are the mussels on Cook Strait (New Zealand) shores? Low seston quality as a possible factor limiting multi-species distributions. Mar. Ecol. Prog. Ser. 194, 123 – 132.
Hawkins, A.J.S., Duarte, P., Fang, J.G., Pascoe, P.L., Zhang, J.H., Zhang, X.L., Zhu, M.Y., 2002. A functional model of responsive suspension-feeding and growth in bivalve shellfish, configured and validated for the scallop Chlamys farreri during culture in China. J. Exp. Mar. Biol. Ecol. 281, 13 – 41. He, C.B., Xu, S.J., Zhang, C., 1997. Study on the growth and ecological characteristics of Meretrix meretrix cultivated on tidal flat. Chin. J. Fish. Sc. 16, 17 – 20. Jorgensen, C.B., 1943. On the water transport through the gills of bivalves. Acta Physiol. Scand. 5, 297 – 304. Kuang, S.H., Fang, J.G., Sun, H.L., Li, F., 1996. Seasonal variation of filtration rate and assimilation efficiency of scallop, Chlamys farreri, in Sanggou Bay. Oceanol. Limnol. Sinica 27, 194 – 199. Lin, Z.H., Xu, Z.Z., 1997. The effect of temperature and salinity on the development of Meretrix meretrix. J. Fujian Fish. 1, 27 – 33. MacDonald, B.A., Bacon, G.S., Ward, J.E., 1998. Physiological responses of infaunal (Mya arenaria) and epifaunal (Placopecten magellanicus) bivalves to variation in the concentration and quality of suspended particles II. Absorption efficiency and scope for growth. J. Exp. Mar. Biol. Ecol. 219, 127 – 141. Navarro, J.M., Gonzalez, C.M., 1998. Physiological responses of Chilean scallop, Argopecten purpuratus, to decreasing salinity. Aquaculture 167, 315 – 327. Sun, H.L., Fang, J.G., Kuang, S.H., Li, F., 1995. Filtration rate of scallop, Chlamys farreri, cultured in simulated natural environment. Chin. J. Fish. Sci. 2, 16 – 21. Ward, J.E., Shumway, S.E., 2004. Separating the grain from the chaff: particle selection in suspension- and deposit-feeding bivalves. J. Exp. Mar. Biol. Ecol. 300, 80 – 130. Wong, W.H., Cheung, S.G., 2001. Feeding rhythm of the greenlipped mussel, Perna viridis (Linnaeus, 1785) (Bivalvia: Mytillidae), during spring and neap tidal cycles. J. Exp. Mar. Biol. Ecol. 257, 13 – 36. Wu, G.H., Chen, P.J., Hang, R.S., Yang, S.Y., Shen, J.L., 2002. Influence of salinity and day and night rhythm on feeding rate (FR) of Ruditapes philippinarum. J. Oceanogr. Taiwan Strait 21, 72 – 77. Yamamuro, M., Hiratsuka, J., Ishitobi, Y., 2000. Seasonal change in a filter-feeding bivalve, Musculista senhousia, population of a eutrophic estuarine lagoon. J. Mar. Syst. 26, 117 – 126. Yang, X.X., Lin, X.T., Ji, X.L., 2000. The effects of light intensity, temperature and salinity on filtration rate of Perna viridis. Chin. J. Mar. Sci. 24, 36 – 38. Yantai Ocean and Fishery Bureau, 2002. Observation Reports on Oceanographic Factors in Yantai Regions of Bohai Sea and Yellow Sea. Shandong Scientific and Technical Press, Jinan. 254 pp. Zhuang, S.H., Wang, Z.Q., 2004. Influence of size, habitat and food concentration on the feeding ecology of the bivalve, Meretrix meretrix Linnaeus. Aquaculture 241, 689 – 699. Zhuang, S.H., Zhang, M., Zhang, X.L., Wang, Z.Q., 2004. The influence of body size, habitat and diet concentration on feeding of Laternula marilina Reeve. Aquac. Res. 35, 622 – 628.
The influence of salinity, diurnal rhythm and daylength on feeding behavior in Meretrix meretrix Linnaeus Shuhong Zhuang * Biological Science and Chemical Engineering School, Yantai University, Yantai 264005, China Received 27 September 2004; received in revised form 20 June 2005; accepted 21 July 2005
Abstract A nature-simulating culture system was used to explore the influence of salinity, the diurnal cycle and daylength on ingestion rate (IR) and assimilation efficiency (AE) of Meretrix meretrix. The clams used in the experiments were grouped into three sizes: small, with a shell length of 2.70 F 0.10 cm and a dry fresh weight of 0.35 F 0.04 g; medium, with a shell length of 4.00 F 0.05 cm and a dry fresh weight of 1.25 F 0.05 g; and large, with a shell length of 5.00 F 0.10 cm and a dry fresh weight of 2.45 F 0.10 g. The clams in all size groups demonstrated a common response pattern in IR and AE under salinities ranging from 18 to 34 ppt. The clams achieved the greatest IR within the salinity range 27 to 30 ppt. There was a marked reduction in IR outside this range. Of the salinities tested 18 ppt was the harshest stress to the feeding of M. meretrix. Between the salinities 24 to 34 ppt, changes in AE of the clam were the inverse of those observed in IR, suggesting that M. meretrix is able to compensate for the loss of IR by an increase in AE. Although the effect of both salinity and body size of the clam was significant on both IR and AE, salinity had evidently stronger influence than body size. All sizes of clam showed a three-phase diurnal feeding pattern: a high ingestion phase from 00:00 to 08:00, a low ingestion phase from 12:00 to 20:00, and a changing phase between low and high ingestion phases. The IR response to daylength comprised a high and constant feeding phase at daylengths from 0 to 16 h (longer darkness) and a declining and unstable feeding phase as daylength increased from 16 to 24 h (shorter darkness). All sizes of clams demonstrated an inverse adaptation to AE compared with IR, indicating that the clam is able to achieve a stable feeding physiology by compensating for daylength-induced variations in IR by changing AE. The ANOVA analysis also showed that both diurnal cycle and daylength affected IR and AE of the clam very significantly, body size did not, however. D 2005 Elsevier B.V. All rights reserved. Keywords: Meretrix meretrix; Ingestion rate; Assimilation efficiency; Salinity; Diurnal cycle; Daylength
1. Introduction
* Fax: +86 535 6902063. E-mail addresses: [email protected], [email protected]. 0044-8486/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2005.07.036
Meretrix meretrix L. is a nearly equilateral, triangular shaped clam with highly coloured shells. It inhabits sandy substrates in the lower intertidal and shallow subtidal areas of the Bohai and western Yel-
S. Zhuang / Aquaculture 252 (2006) 584–590
low Seas. For several years this clam has been cultured by the native farmers of the Shandong Peninsula, China because of its relatively high meat yield, delicious and tender taste and ease of culture in the natural habitat as well as for its attractive appearance (He et al., 1997; Zhuang and Wang, 2004). The feeding physiology and ecology of bivalves, particularly cultured species, have been widely studied for decades. In these studies, physiological and ecological parameters, such as clearance rate, ingestion rate, assimilation efficiency and scope for growth, have been widely used in considering the energetic budget and nutrient cycles (Aldridge et al., 1995; Fang et al., 1996; Kuang et al., 1996; MacDonald et al., 1998; Hawkins et al., 2002). In a previous study, the feeding physiology of M. meretrix on a laboratory scale was preliminary to a further determination of economical farming densities and environmental carrying capacity in the local intertidal zones and shallow sub-littoral areas (Zhuang et al., 2004). In order to highlight feeding behavior under different culture circumstance, this subsequent study was focused particularly on the variation of ingestion rate and assimilation efficiency as influenced by salinity, diurnal cycle and daylength. There is currently no information on these aspects of the physiology of this species in the scientific literature.
2. Materials and methods 2.1. Clams used in the experiments A range of sizes of M. meretrix to support the experiments was collected from the intertidal zone of the local island of Changshan archipelago in July 2003. The collected clams were grouped into 3 sizes: small, with a shell length of 2.70 F 0.10 cm and a dry fresh weight of 0.35 F 0.04 g; medium, with a shell length of 4.00 F 0.05 cm and a dry fresh weight of 1.25 F 0.05 g; and large, with a shell length of 5.00 F 0.10 cm and a dry fresh weight of 2.45 F 0.10 g. The healthy clams were acclimated for at least one week in a acclimation tank of the laboratory culture system to an ambient temperature of 16–18 8C and a natural diurnal cycle of 13 h light / 11 h dark. After acclimation healthy individuals were selected for each experiment. During the acclimation the diet type and
585
concentration in the culture tanks were identical to those used in the experiments. 2.2. Experimental methods The experiments were carried out in the marine propagation center of the Changdao Institute of Marine Aquaculture between August and October 2003. A tank culture system was set up to simulate the natural environment of the clam with regard to both water and substrate. Seawater was first pumped into a large (100 m3) sedimentation container and then into a smaller reservoir. The latter functioned as a water pressure regulator and an inflow diet concentration regulator to maintain a constant flow of water with constant diet concentration into the 40 40 45 cm deep culture tanks in which the clams were held. The clams were stocked at a density of 10 per tank. Each experiment comprised four replicate culture tanks and two controls that were used to eliminate the influence of both diet propagation (such as microalgae) and sedimentation as experimental variables. During the experiments the diet concentration in the inflow and outflow water was microscopically monitored. The diet concentration of inflow water was regulated by adding the microalga, Isochrysis zhanjangensis, to the reservoir tank. For each experiment the shell length and dry weight of both the shell and the flesh of the clam were precisely measured. To determine the effect of salinity, the feeding pattern of the clam was observed for three days at each of the following five salinities: 18, 23, 27, 30 and 34 ppt (NaCl) which were diluted with fresh water or strengthened with sea salt. The treatment of salinities was separate with the test sequence from 18 to 34 ppt. After a salinity treatment had been finished, the salinity in the reservoir was regulated for next salinity treatment and the clam in the culture tank was renewed from the acclimation tank. The salinity of the culture water was measured with a salinometer (Jenco-3107). For observation of the feeding rhythm of the clam during the diurnal cycle, a normal cycle of 12 h light (06:00 to 18:00 h) / 12 h dark (18:00 to 06:00 h) was chosen to obtain a generalized and unstressed feeding pattern. The light intensity used in the light period was 9.8 W m 2 (on the water surface of the culture tank) which was about the average light intensity at the
586
S. Zhuang / Aquaculture 252 (2006) 584–590
local coast (Yantai Ocean and Fishery Bureau, 2002). This light intensity was also used to determine the effect of various daylengths (0, 4, 8, 12, 16, 20 and 24 h light) on feeding. The treatments of different daylengths used in the experiment were 0 h light / 24 h dark, 4 h light / 20 h dark, 8 h light / 16 h dark, 12 h light / 12 h dark, 16 h light / 8 h dark, 20 h light / 4 h dark, and 24 h light / 0 h dark, respectively. In the experiment the clam was observed for three days. The data used in the study was a mean of measured data in each three-day experiment. All treatments were done separately and in all experiments water samples were taken every 4 h for the measurement of feeding activities of the clams. In the dark period, samples were taken with a dim red light that avoided imposing light stress on the feeding of the clam. In and around the culture room man-made sounds and disturbances were minimized during the observation periods. The experiments were carried out at ambient water temperatures (i.e. 16–18 8C). The diet concentration (microalga) was maintained at 0.7–0.9 106 cells L 1 and the flow velocity of the seawater from the smaller reservoir container to the culture tank at 80–100 L min 1. This provided the
standard against which the experimental deviation of ingestion rate and assimilation efficiency of M. meretrix was measured. During the experiment there was no pseudofaeces produced by the clam. After each treatment with salinity and daylength in the experiments, a sub-sample of faecal material was collected from 6 chambers containing a clam under the same treatment conditions using a pipette and without disturbing the feeding clams. The faecal sample was concentrated onto pre-weighted Whatman GF/C filters for dry weight and ash-free dry weight determination (Gardner, 2000). The diet concentration was indicated by the content of total particulate matter (TPM) and particulate organic matter (POM) in the seawater of the culture tank. TPM and POM were determined following the procedures described by Bayne and Newell (1983), Sun et al. (1995) and Dong et al. (2000). A sample of water (1000 ml) was first vacuum filtered through marked GF/C Whatman glass–fiber filters (mesh 1.2 Am) which had been burned at 450 8C for 6 h before weighing (W 0). The filtered material was rinsed with 0.5 mol L 1 NH4COOH to get rid of the salts before being dried at 110 8C for 12 h and weighed to get the
1.6
IR (mg g-1 h-1)
1.4 1.2 1.0 0.8
Small (Mean ± SD) Medium (Mean ± SD) Large (Mean ± SD)
0.6 0.4 0.2 18
23
27
30
34
Salinity (ppt) 80
AE (%)
70 60 50 40 18
23
27
30
34
Salinity (ppt) Fig. 1. The effect of salinity on ingestion rate (IR) and assimilation efficiency (AR) of three size groups of Meretrix meretrix.
S. Zhuang / Aquaculture 252 (2006) 584–590 Table 1 ANOVA testing for the effects of salinity and body size upon IR and AE of Meretrix meretrix Item
Source
df
SS
IR
Salinity Body size Error Total Salinity Body size Error Total
4 2 8 14 4 2 8 14
2.5693 0.0973 0.0627 2.7293 836.9693 11.8813 41.5387 890.3893
AE
MS
F
P
0.6423 0.0487 0.0078
82.00 6.21
0.0000** 0.0235*
209.2423 5.9407 5.1923
40.30 1.14
0.0001** 0.3656
first dry weight (W 110). This was re-weighed after burning at 450 8C for 6 h to give the second dry weight (W 450). Finally, TPM and POM were calculated as following respectively, TPM ¼ W110 W0 ;
POM ¼ W110 W450 :
587
the experiment; Ceo and Cet the diet concentration in the inflow and outflow water of the culture tank respectively (mg L 1); t the duration of the experiment; Sed refers to the coefficient of variation in the diet concentration of controls; Cco and Cct the diet concentration in the inflow and outflow water of the culture tank in the control, respectively (mg L 1). 2.3.2. Assimilation efficiency Assimilation efficiency (AE %) was determined following Conover (1966): AE ¼ 100 ð FV EVÞ=½ð1 EVÞ FV where FV refers to the percentage of assimilated diet weight minus ash in the total assimilated diet weight; EVthe percentage of faeces (dry weight) minus ash in the total excreted faeces.
2.3. Computing methods
3. Results
2.3.1. Ingestion rate Ingestion rate (IR, mg g 1 h 1) was calculated as follows (Jorgensen, 1943; Zhuang et al., 2004; Zhuang and Wang, 2004):
3.1. Salinity influences on IR and AE
IR ¼ V ½Ceo ðCeo SedÞ Cet=ð M t Þ Sed ¼ ðCco CctÞ=Cco where V refers to the volume of the culture tank (L); M the dry weight of the soft part of the clams used in
The results show that the IR of all sizes of clam was highest at salinities of 27–30 ppt and decreased either side of this range (Fig. 1). And AE for all sizes of the clam was lowest at 18 ppt, reaching its highest value at 23 ppt. Over this salinity AE decreased, remained relatively constant from 27 to 30 ppt and then slightly increased. Based on these responses of
1.5
IR (mg g-1 h-1)
1.2 0.9 0.6 Small (Mean± SD) Medium (Mean± SD) Large (Mean± SD)
0.3 0.0 12:00 Light
16:00 Light
20:00 Dark
0:00 Dark
04:00 Dark
08:00 Light
Time Fig. 2. The diurnal pattern of ingestion rate of three size groups of Meretrix meretrix exposed to a 12 h light (06:00 to 18:00 h) / 12 h dark (18:00 to 06:00 h) cycle.
588
S. Zhuang / Aquaculture 252 (2006) 584–590
Table 2 ANOVA testing for the effects of feeding time upon IR of Meretrix meretrix Item
Source
df
SS
MS
F
P
IR
Feeding time Body size Error Total
5 2 10 17
1.0593 0.0088 0.0224 1.0905
0.2119 0.0044 0.0022
94.77 1.98
0.0000** 0.1889
IR and AE, a salinity of 18 ppt appears to be a relatively harsh stress with regard to the feeding physiology of the clam. It is statistically (ANOVA) shown that both size-related and salinity-related differences in IR and AE of the clam were significantly different, respectively P b 0.05 and P b 0.001, however, the salinity had more influence than body size of the clam on IR and AE (Table 1). 3.2. Feeding rhythm during a diurnal cycle
IR (mg g-1 h-1)
The feeding pattern, as indicated by IR, during a 12 h light / 12 h dark diurnal cycle was similar for all
sizes of clams (Fig. 2). It had three phases: a high ingestion phase from 00:00 to 08:00 h, a low ingestion phase from 12:00 to 20:00 h, and a changing phase between 20:00 and 00:00 h in which there was a sharp increase in IR from the low to the high feeding phase. For all clams the highest IR was observed at 00:00 h. In this normal diurnal cycle the clams with different sizes showed no difference in IR, but significant differences were found between different feeding times for all three sizes of clams (Table 2.). The feeding time exerted more influence on IR than the body size of the clam. 3.3. Impact of daylength on IR and AE The relationship between food ingestion (as indicated by IR) and daylength could be divided into two types: a high and constant level of feeding at daylengths from 0 (total dark) to 16 h, and a declining and less stable level of feeding with further increases in daylength from 16 to 24 h (total light) (Fig. 3). However, small clams did not conform to this pattern, the
1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0
4
8
12
16
20
24
Day length (h) 75
AE (%)
70 65 60 Small (Mean± SD) Medium (Mean± SD) (Mean± SD) Large
55 50 0
4
8
12
16
20
24
Day length (h) Fig. 3. The effect of daylength on ingestion rate (IR) and assimilation efficiency (AE) of three size groups of Meretrix meretrix.
S. Zhuang / Aquaculture 252 (2006) 584–590 Table 3 ANOVA testing for the effects of daylength and body size upon IR and AE of Meretrix meretrix Item
Source
df
SS
IR
Daylength Body size Error Total Daylength Body size Error Total
6 2 12 20 6 2 12 20
0.7038 0.0028 0.0192 0.7257 324.0057 0.0152 26.4314 350.4524
AE
MS
F
P
0.1173 0.0014 0.0016
73.49 0.87
0.0000** 0.4433
54.0010 0.0076 2.2026
24.52 0.00
0.0001** 0.9965
decline in their IR being continuous throughout the whole range of daylengths. It should be noted that the IR of small clams at daylengths less than 12 h was higher than that of the larger clams, but lower at daylengths above 12 h. Regarding to changes in AE with increasing daylength, all sizes of clams displayed a contrary pattern to that shown for IR, i.e. AE increased continuously with increasing daylength (Fig. 3). Similarly, the influence of body size on both IR and AE was insignificant, but that of daylength was very significant ( P b 0.001) (Table 3).
4. Discussion Like most marine bivalves, salinity is one of the most important factors influencing the feeding of M. meretrix. In agreement with the study on feeding activity of Chilean scallop (27–30 ppt) by Navarro and Gonzalez (1998), Perna viridis (optimum range: 26–30 ppt) by Yang et al. (2000) and Manila clam (optimum range: 25–30 ppt) by Wu et al. (2002), the optimum salinity for IR of M. meretrix was found to be similar in the range between 27 and 30 ppt which is consistent with the study made by Lin and Xu on the same species (Lin and Xu, 1997). It is found that the place most inhabited by this clam in the local intertidal zone is far from the estuary where the salinity is relatively low and fluctuates greatly (Lin and Xu, 1997). This range of salinity tolerance and the optimum salinity for growth of M. meretrix will be very helpful and instructive for the local farmers who live around the Bohai Gulf to which many rivers lead, resulting in a large range in salinity (24–30 ppt) near the estuaries (Yantai Ocean and Fishery Bureau, 2002). Our data will facilitate the selection of optimal
589
intertidal areas to cultivate this clam. The phenomenon observed in the experiment that the response to AE of the clam was the converse of that shown to IR within a certain range of salinity (23–34 ppt), suggests that ingestion, assimilation and metabolism would be closely related and coordinated in the feeding physiology of M. meretrix. This supports the contention that the clam could compensate to a certain extent for a reduction in ingestion rate, through severe salinity or other environmental impacts, with higher levels of assimilation efficiency and even metabolic levels (Beiras et al., 1995; Navarro and Gonzalez, 1998; Bayne and Newell, 1983; Wu et al., 2002). The feeding rhythm of M. meretrix under the diurnal cycle 12 h light / 12 h dark used in this study coincides well with that of Manila clam Ruditapes philippinarum as described by Wu et al. (2002). They suggested that bivalves living within a similar habitat and experiencing similar environmental influences would have a similar feeding rhythm. The distinct three phases of the feeding rhythm of all sizes of the clam clearly suggest that this feeding rhythm would be mainly attributed to the light/dark cycle which could affect the movement and availability of their food (Yamamuro et al., 2000; Wong and Chueng, 2001; Wu et al., 2002). Although it is not possible to determine the smallest size at which the clam demonstrates this biological feeding rhythm, this study shows that M. meretrix larger than 2.70 cm in size has the same day/night feeding rhythm. As in other bivalves, the biological feeding rhythm of M. meretrix is the result of long-term co-influences of diet availability, light, temperature and tidal movement on the clam. This inherent feeding rhythm of bivalves is demonstrable even if the variable factors are absent (Yang et al., 2000; Wu et al., 2002). Since the feeding of activity of M. meretrix shows a marked nocturnal form the species is able to achieve a higher feeding level in a shorter day and a lower one in a longer day. The approximately inverse responses of IR and AE to an increase in daylength demonstrate again that the clam compensates for a reduction in IR by an increased AE, on this occasion under the influence of changing daylengths. As to the inverse response of the clam in IR and AE, there is a number of ways that bivalves can respond to food availability (Ward and Shumway, 2004). Prior-ingestive selection outside the stomach
590
S. Zhuang / Aquaculture 252 (2006) 584–590
and post-ingestive selection in the stomach (Brillant and MacDonald, 2000) which enable the bivalve in nature to have a different gut retention time for organic and inorganic particles could help the animals balance IR and AE for maintaining an optimal physiological metabolism. Also by adjusting feeding rates and enzymatic activities, AE in bivalves was able to remain constant, irrespective of the changes in food availability (Wong and Cheung, 2001).
Acknowledgements The author is very grateful to the technical cooperation with the Changdao Department of Marine and Aquatic Production for their assistance and support in building the culture system and to Dr. Neil Bourne, Pacific Biological Station, Nanaimo, for revising the MS.
References Aldridge, D.W., Payne, B.S., Miller, A.C., 1995. Oxygen consumption, nitrogenous excretion and filtration rates of Dreissena polymorpha at temperatures between 20–32 8C. Can. J. Fish. Aquat. Sci. 52, 761 – 767. Bayne, B.L., Newell, R.C., 1983. Physiological energetics of marine molluscs. In: Saleuddin, A.S.M., Wilbur, K.M. (Eds.), The Mollusca, Vol.4. Physiology, Part I. Academic Press, New York, pp. 407 – 515. Beiras, R., Camacho, A.P., Albentosa, M., 1995. Short-term and long-term alteration in the energy budget of young oyster Ostrea edulis L. in response to temperature change. J. Exp. Mar. Biol. Ecol. 186, 221 – 236. Brillant, M.G.S., MacDonald, B.A., 2000. Postingestive selection in the sea scallop, Placopecten magellanicus (Gmelin): the role of particle size and density. J. Exp. Mar. Biol. Ecol. 253, 211 – 227. Conover, R.J., 1966. Assimilation of organic matter by zooplankton. Limnol. Oceanogr. 22, 338 – 354. Dong, B., Xue, Q.Z., Li, J., 2000. Environmental factors affecting the feeding physiological ecology of Manila clam, Ruditapes philippinarum. Oceanol. Limnol. Sinica 31, 636 – 642. Fang, J.G., Kuang, S.H., Sun, H.L., Li, F., 1996. Study on the carrying capacity of Sanggou Bay for the culture of scallop Chlamys farreri. Chin. J. Mar. Fish. Res. 17, 18 – 31. Gardner, J.P.A., 2000. Where are the mussels on Cook Strait (New Zealand) shores? Low seston quality as a possible factor limiting multi-species distributions. Mar. Ecol. Prog. Ser. 194, 123 – 132.
Hawkins, A.J.S., Duarte, P., Fang, J.G., Pascoe, P.L., Zhang, J.H., Zhang, X.L., Zhu, M.Y., 2002. A functional model of responsive suspension-feeding and growth in bivalve shellfish, configured and validated for the scallop Chlamys farreri during culture in China. J. Exp. Mar. Biol. Ecol. 281, 13 – 41. He, C.B., Xu, S.J., Zhang, C., 1997. Study on the growth and ecological characteristics of Meretrix meretrix cultivated on tidal flat. Chin. J. Fish. Sc. 16, 17 – 20. Jorgensen, C.B., 1943. On the water transport through the gills of bivalves. Acta Physiol. Scand. 5, 297 – 304. Kuang, S.H., Fang, J.G., Sun, H.L., Li, F., 1996. Seasonal variation of filtration rate and assimilation efficiency of scallop, Chlamys farreri, in Sanggou Bay. Oceanol. Limnol. Sinica 27, 194 – 199. Lin, Z.H., Xu, Z.Z., 1997. The effect of temperature and salinity on the development of Meretrix meretrix. J. Fujian Fish. 1, 27 – 33. MacDonald, B.A., Bacon, G.S., Ward, J.E., 1998. Physiological responses of infaunal (Mya arenaria) and epifaunal (Placopecten magellanicus) bivalves to variation in the concentration and quality of suspended particles II. Absorption efficiency and scope for growth. J. Exp. Mar. Biol. Ecol. 219, 127 – 141. Navarro, J.M., Gonzalez, C.M., 1998. Physiological responses of Chilean scallop, Argopecten purpuratus, to decreasing salinity. Aquaculture 167, 315 – 327. Sun, H.L., Fang, J.G., Kuang, S.H., Li, F., 1995. Filtration rate of scallop, Chlamys farreri, cultured in simulated natural environment. Chin. J. Fish. Sci. 2, 16 – 21. Ward, J.E., Shumway, S.E., 2004. Separating the grain from the chaff: particle selection in suspension- and deposit-feeding bivalves. J. Exp. Mar. Biol. Ecol. 300, 80 – 130. Wong, W.H., Cheung, S.G., 2001. Feeding rhythm of the greenlipped mussel, Perna viridis (Linnaeus, 1785) (Bivalvia: Mytillidae), during spring and neap tidal cycles. J. Exp. Mar. Biol. Ecol. 257, 13 – 36. Wu, G.H., Chen, P.J., Hang, R.S., Yang, S.Y., Shen, J.L., 2002. Influence of salinity and day and night rhythm on feeding rate (FR) of Ruditapes philippinarum. J. Oceanogr. Taiwan Strait 21, 72 – 77. Yamamuro, M., Hiratsuka, J., Ishitobi, Y., 2000. Seasonal change in a filter-feeding bivalve, Musculista senhousia, population of a eutrophic estuarine lagoon. J. Mar. Syst. 26, 117 – 126. Yang, X.X., Lin, X.T., Ji, X.L., 2000. The effects of light intensity, temperature and salinity on filtration rate of Perna viridis. Chin. J. Mar. Sci. 24, 36 – 38. Yantai Ocean and Fishery Bureau, 2002. Observation Reports on Oceanographic Factors in Yantai Regions of Bohai Sea and Yellow Sea. Shandong Scientific and Technical Press, Jinan. 254 pp. Zhuang, S.H., Wang, Z.Q., 2004. Influence of size, habitat and food concentration on the feeding ecology of the bivalve, Meretrix meretrix Linnaeus. Aquaculture 241, 689 – 699. Zhuang, S.H., Zhang, M., Zhang, X.L., Wang, Z.Q., 2004. The influence of body size, habitat and diet concentration on feeding of Laternula marilina Reeve. Aquac. Res. 35, 622 – 628.