- Email: [email protected]
Some effects of light intensity and photoperiod on the sea bass larvae (Dicentrarchus labrax (L.)) reared at the Centre Oceanologique de Bretagne
Aquaculture, 17 (1979) 311-321 1~ Elsevier ;Scientific Publishing Company,
Amsterdam
-
Printed
in The Netherlands
313
SOME EFFECTS OF LIGHT INTENSITY AND PHOTOPERIOD ON THE SEA BASS LARVAE (DICENTRARCHUS LABRAX (L.)) REARED AT THE CENTRE OCEANOLOGIQUE DE BRETAGNE
MARIA
HELENA
Faculdade Contribution (Accepted
BARAHONA-FERNANDES
de Cicncias, no. 625 1 March
Departamento
de Zoologia,
du Ddpartement
Scientifique
Lisbon
(Portugal)
du Centre
Oceanologique
de Bretagne
1979)
ABSTRACT Barahona-Fernandes, M.H., 1979. Some effects of light intensity and photoperiod sea bass larvae (Dicentrarchus labrax (L.)) reared at the Centre Oceanologique Bretagne. Aquaculture, 17: 311-321.
on the de
Four experiments were performed to determine the effects of light intensity on the growth and survival of sea bass larvae; two experiments dealt with the photoperiod and two with the combined effects of light intensity and the photoperiod. Recently hatched larvae from the same spawning were used within each experiment. The light intensity experiments show that there is better growth but poorer survival at higher light intensities. The photoperiod experiments show a better growth at 18 h photoperiod and a better survival at 12 h exposure to light. The study of the combined effects of light intensity and photoperiod confirmed the hypothesis that strong light intensities are lethal to newly hatched larvae (with no pigmentation). If the light intensity is lowered during the first week, the best rearing conditions were found to be continuous lighting relative to survival rate, and 14-16 h photoperiod relative to growth.
INTRODI’CTION
It is wlell known that marine fish larvae are positively phototropic and that feeding is greatly facilitated by a high light intensity, in accordance with the importance of vision to particulate planktonophagic fishes. In the rearing systems studied, all authors used bright light which was above the general threshold at first feeding, above l-10 lux (Blaxter, 1968). Alessio (1975) found no differences in the results of Sparus auruta larvae reared from 300 to 10,000 lux. Riley and Thacker (1963) and Houde and Palko (1970) had a poorer survival at the lower light intensity with Pleuronectes platessa and Harengula pensacolae, but did not give the light intensities used. The searching volume of Clupea harengus per day was not affected by changes in light intensity from 10 to 1,000 lux (Rosenthal and Hempel, 1971). Blaxter (1968,1!373), Houde and Palko (1970), Houde (1973,1976) and Stepien
312
(1976) found that fish larvae are incapable of eating in complete darkness. The possible effect of the photoperiod on the growth of fish larvae is not often considered as an independent controlling factor, although its role int the reproductive cycles has been extensively studied (Htun-Han, 1977). Huh et al. (1976) studied the growth rates of Perca fluvescens and concluded that they were nearly three times greater with 16 h light than with only 8 h. Gross et al. (1965) found that the growth and the food conversion efficiency of Lepomis cyanellus were higher with 16 h than 8 h of light. Nevertheless, most of the authors use continuous light for rearing marine fish larvae (O’Connell and Raymond, 1970; Struhsaker et al., 1973; Fliichter, 1974; Spectorova et al., 1974; Barnabe, 1976; Villani, 1976; Ramos, 1977). Others use different photoperiods, from 10 to 16 h light, without any explanation about their choice (Riley, 1966; Ryland, 1966; Blaxter, 1968; Lasker et al., 1970; Rosenthal and Hempel, 1970; Alderson and Bromley, 1973; Howell, 1973; Alessio, 1975; Girin et al., 1975; Alessio et al., 1976; Houde, 1976; Laurence, 1976; Stepien, 1976; Bromley, 1977). This paper is a study of the effects of changing the light intensity and the photoperiod on sea bass larvae in reference to their growth, survival and condition coefficient. MATERIAL
AND METHODS
The general rearing schema was the same as described by Barahona-Fernandes (1978a,b,c) and Fuchs (1978). Four experiments were performed to determine the effects of light intensity, two on the effects of the photoperiod and two on the combined effects of light intensity and photoperiod. The water in the tanks was thermoregulated at 19 i 1°C and the oxygen level was kept between 88 and 110% (5.73 ml/l and 6.69 ml/l). The water flow increased up to 40 l/h in the 150 1 tanks and up to 20 l/h in the 60 1 tanks. The rearing tanks were cylindroconical, 150 1 capacity for the light intensity and 60 1 capacity for the photoperiod studies. All rearing tanks were lighted by two 20 watt “Grolux” fluorescent tubes (day light type) suspended 30 cm above the tank surface and giving light intensity at the water surface from 1,400 to 3,500 lux during the night, and 2,000 to 3,500 lux during the day. These differences were due to the natural daylight coming through the room windows. The desired changes in the light intensity were obtained by sticking black PVC sheet covering to different areas of the lamps. The photoperiod experiments were made in a series of three 60 1 tanks, one under continuous lighting and two enclosed in wooden boxes with their lamps connected to a time clock giving 18 and 12 h light periods (from 1 a.m. to 7 p.m. and from 7 a.m. to 7 p.m. respectively). In all experiments on light intensity effects, one tank was under strong light intensity (1,400-3,500 lux) and a second one received light filtered through the plastic PVC, from which the light intensities indicated in Table I
313 TABLE
I
Initial larval number confidence intervals
and density, percentage for 95% in the different
Experiment
of survival, experiments
condition coefficient with the on light intensity effects
Initial larval density and larval number
Final survival
.._______ 1,400--3,500 lux tank 303700 lux tank
42 larvae/l (6,300 1)
19.8% 23.4%
Final condition coefficient --0.44 + 0.03 0.29 !C0.03
II
1,403-3,500 lux tank 303700 lux tank
60 larvae/l (9,000 1)
6.3% 16.9%
0.39 f 0.03 0.38 f 0.02
III
1,403-3,500 lux tank 303- 1000 lux tank
60 larvae/l (9,000 1)
10.3% 16.1%
0.42 + 0.02 0.37 * 0.01
IV
1,403-3,500 lux tank 1513-- 800 lux tank
60 larvae/l (9,000 1)
8.6% 21.2%
0.47 t 0.01 0.40 + 0.05
I
resulted. In the photoperiod experiments, one tank was also under continuous strong light intensity (1,400-3,500 lux) and the other two tanks, enclosed in the wooden boxes, had total darkness during the dark periods and 2,0003,500 lux during the light periods. In the experiments on the combined effects of light intensity and photoperiod, these last installations were used, but during the first 7 days the light intensity was reduced in all tanks to :5
4
f
A
Fig. 1. Growth curves of the larvae in the four experiments effect, with the mean values and their confidence intervals intensity tank; (-) lower light intensity tank.
A
performed on light intensity for 95%. (- - -) high light
314
800-1,000 lux. At 7 days, the larvae are already pigmented and the light intensity can then be increased. The initial density of larvae in the tanks varied from 43 to 70 per liter and, within each experiment, they were from the same spawning. The larvae used in Expt. I on the effects of light intensity and the ones used in Expt. a in the photoperiod effects were from the same spawning. Every 10 days, a sample of 10 fish was removed from each tank and preserved in 5% neutralized formalin for later measurements and weighing. Every day the tanks were cleaned of the detritus accumulated at the bottom. The feeding schema was the same as described by Barahona-Fernandes and Girin (1977). Brachionus plicatilis was given from day 3 to day 15, reaching a maximum of 7.5 prey/ml; Artemia salina nauplii were distributed from day 10 onwards, reaching a maximum of 0.1-2 prey/ml. All these amounts correspond to the estimated necessary feeding needs for 24 h. RESULTS
The growth curves with the mean values of the samples and their 95% intervals of confidence for the light intensity effect9 are shown in Fig. 1. The analysis of variance highlights the significantly better growth of the larvae under strong light intensities: in Expt. I, F,,l, = 42.13**; in Expt. II, F,,,, = 5.69**; in Expt. III, F1,18 = 11.33**; and in Expt. IV, Fills = 9.66”“. Table I gives the initial number of larvae and the final survival, both as percentage and in number of survivors, and the condition coefficients with their 95% confidence intervals. It is clear that the best survival were always obtained at lower light intensities and that the best final condition coefficients were always obtained at higher light intensities. The growth curves for the two experiments performed on the photoperiod effects are shown in Fig. 2 with the mean values of the samples and with their 95% confidence intervals. The analysis of varience with orthogonal breakdown revealed that the significant differences between the treatments are due to the better final growth of the larvae at 18 h light (Expt. a, F,,26 = 28.28”, and Expt. b, F,,,, = 4.45’). The initial larvae number, the final survival and the final condition coefficient with their confidence intervals for 95% are given in Table II for the photoperiod experiments. The best survival was obtained at 12 h and the highest final condition coefficient at 18 h light. As the larvae used in Expt. I on the light intensity effects and those used in Expt. a on the photoperiod effects were from the same spawning, it was possible to compare the growth in the same light and photoperiod conditions (continuous 1,400-3,500 lux) in the 150 1 and 60 1 tanks. Although the mean weight of the larvae at 30 days in the 150 1 tank was 10.09 mg and in the 60 1 tank 8.36 mg, the analysis of variance showed no significant differences (F I,18 = 0.503). From the same spawning, the optimum growth was also compared in 150 1 tanks (24 h light at 2,000-3,500 lux) to the optimum growth in the 60 1
315 WET
WEIGHT
(mg )
A
A
32-
28 -’
69
24.
20-
Fig. 2. Grcwth curves of the larvae in the two experiments performed on the photoperiod effects, with the mean values and their confidence intervals for 95%; (-) 24 h light photoperiod; (- - -) 18 h light photoperiod; (- - - - -) 12 h light photoperiod.
tank (18 h light at 2,000-3,500 lux). The mean wet weight in the first case was 10.09 mg and in the second 12.45 mg at 30 days. The analysis of variance did not show significant differences (F1,18 = 1.02). The final survival was better in the 150 1 tanks than in the 60 1 tanks. TABLE
II
Initial larval number and density in the tanks, final survival percentage, and condition coefficient with the confidence intervals for 95% in the different experiments on photoperiod effects .~~~_~.___ Experiment ___a 24 h tank 18 h tank 12 h tank b
24 h tank 18 h tank 12htank
Initial
Final survival
larvae
Final condition coefficient
_ 70 larvae/l (4,200 1)
70 larvae/l (4,200 1)
4.6% 3.8% 9.2%
0.37 0.44 0.37
* 0.05 5 0.03 r 0.04
22.5% 24.2% 51.4%
0.42 0.48 0.37
* 0.06 + 0.03 + 0.02
_
316
The results of t,he t~wo experiment,s performed on the combined effects of the light intensity, and the photoperiod are given in Table III. All tanks contained 3.000 larvae in the beginning of the experiments. The orthogonal breakdown of the total F shows that the growt.h rates at 14 and 16 h light are not significantly different from each other, but are significantly higher than growth under 18 and 24 h light regimes. DISCUSSION
The effects of increasing the light intensity during the rearing period are clear: in all experiments the final growth and the condition coefficients were significantly bet,ter. In natural conditions, the sea bass juvenile is a diurnal feeding fish and increasing the light intensity facilitates the vision and the preving ability; the enhanced feeding ability on the growth rate of fish larvae is obvious (Reynolds and Thomson, 1974). The results of final survival in the light intensity experiments show that fish in two of the experiments had a similar final survival, both at the higher and the lower light intensity; in the other two experiments, the final survival was clewlv lower at higher light intensity. The effects of the photoperiod on the growth during the rearing period are also clear. In both experiments, the best growth was obtained at 18 h light photonerind. The same photoperiod also resulted in higher condition coefficimt,a. An improved growth can also be obtained by increasing the day length art,ificiallv, provided ihere is no physiological upset due to photoperiod or lack of it (Rlaxter, 1968). Fuchs (1978) obtained a better growth of sole larvae under the same conditions with 12 h light but with no difference in the final survival r&es. In the experiments on the combined effects of the photoperiod and the light intensity better survival was obtained under continuous lighting, and b&er growth and condition coefficients at 14 and 16 h light. The best light intensit,v for rearing marine fish larvae varies according to the species. Ales~io (1975) had the same rearing results for gilthead sea bream between 300 and 10.000 lux; with the sea bass larvae reared under a light intensity up to 1.000 liix, significantly poorer growth is obtained than under 2,000 to 3.500 11~~.Riley and Thacker (1963) and Houde and Palko (1970) found lnw~r SV-viva1 in the less illuminated tanks. In t.he experiments reported here, on the light intensity and photoperiod effects only, the best growth has been obtained under continuous and strong light and the hest final survival under 12 h of Lwer light intensity. One possihle explanation for these results was put forward by Alessio (1975), Gabriel (1944) and Nash et al. (1974): strong light intensities before the total pigmentation of the larvae (from eleutheroembryo to pterygiolarvae, according to Rallon (1975)) would be lethal to the fish larvae. It is generally accepted that the larval mortality occurs at the eleutheroembryo stage; it seems logical that the lower light intensities or the shorter periods under strong light in-
Experiment 2
Experiment 1
Final survival (%) 37.1
0.40 ? 0.03
Final condition coefficient
f 2.6
4.2
Final growth (mg)
13.6
0.38 i 0.02
Final condition coefficient
Final survival (%)
7.3
Final growth (mg) ? 3.4
i 3.1
0.9
-
-
0.38 + 0.03
7.8 + 6.3
4.3
-
-
-
0.42 + 0.03
13.5
f 4.1 -r 5.4
i 2.2
8.4
0.44 + 0.03
7.2
0.41 + 0.02
14.3 11.1
-
Fills= 3.93"
F Ill8 = 20.17”
F,,,,= 4.52”
F 4/4s = 5.73”
Results of the experiments on the combined effects of light intensity and photoperiod with the final values of growth, condition coefficient and survival percentage, along with the confidence intervals for 95% and the results of the analysis of variance for the growth and condition coefficient parameters Photoperiod 16 14 24 18 F test (hours light)
TABLE III
318
tensity would therefore decrease the mortality. Results of the experiments reported here seem to be in accordance with this hypothesis. The results of the experiments on the combined effects of the light intensity and the photoperiod show clearly that these two parameters cannot be studied separately and confirm that a strong light intensity before the total pigmentation of the larvae induces a high mortality. It is always difficult to compare laboratory results with natural conditions, but Saville (1971) observed that recently hatched larvae stay close to the sea bottom except when a marked mixing occurs down to the bottom; also, after this stage, in daylight, the larvae have their major distribution in mid-water and upwards. These field observations seem to be in agreement with the results reported in this paper. Once the factor that screened the real effects of the photoperiod is found and eliminated, it becomes clear that the sea bass larvae have a significantly better growth under the photoperiod to the geographic limits of the species (36”N to 50”N, i.e., areas from 9 h 43 min to 14 h 30 min - 36”N - and from 8 h 03 min to 16 h 18 min - 50”N); but the best survival is obtained under continuous lighting. Alderson and Bromley (1973), Lasker (1976) and Laurence (1976) proved the low predatory capacity of the young larval stages. Under continuous lighting the chances of meeting prey-larvae increase; the risks of under feeding decrease. The importance of this last factor on the larval survival is well known (Houde, 1973). But the growth is somewhat affected by forcing the larvae to remain active beyond the time they would be under natural environmental conditions. The comparison of the growth capacities of each spawning confirms that, in the same rearing conditions, they are significantly different (BarahonaFernandes, 197810). In the experiments reported here, the mean wet weights of the larvae at 30 days varied from 4.26 to 10.38 mg. The increase of the larval growth, within each spawning, obtained by changing the rearing conditions into the most favourable ones, can balance the annual fluctuations between the growth capacity of the different spawnings. CONCLUSION
The present work shows that light intensity and photoperiod studies cannot be performed separately. If the light intensities are constant, the photoperiod studies would lead to the choice of the 18 h photoperiod for the best growth and the 12 h photoperiod for the best final survival results. If the light intensity is lower during the first 7 days after hatching (period of progressive pigmentation of the larvae), then the best final survival is obtained under continuous lighting, and the best growth with a photoperiod of 14 to 16 h. Further studies should be carried out in order to determine the optimal pattern of light intensity and photoperiod for sea bass larvae.
319
ACKNOWLEDGEMENTS
The author acknowledges a fellowship from the French Government through the Frenlsh Embassy in Lisbon, and also wishes to thank A. and L. Laubier and M. Girin for the critical reading of the manuscript, and G. Hekinian for his help.
Barahona-Fernandes, M.H., 1979. Quelques aspects des effets de 1’intensitC lummeuse et de la photopCriode sur les larves du bar (Dicentrarchus la brax (L. )) BlevCes au Centre Ockanologique de Bretagne. Aquaculture, 17: 311-321 (en anglais). Huit es.p&iences ont CtC menees sur les effets de la lumiere sur la croissance et la survie des larves de bar de l’&losion B 1 mois: quatre exp&iences sur 1’intensitC lumineuse, deux exp&iencc:s sur la photoperiode et deux expGriences sur l’action cornbinGe de l’intensite lumineuse et de la photop&iode. Dans chaque expgrience, des larves issues de la mdme ponte ont BtB utilis8es. Les plus fortes intensites lumineuses donnent la meilleure croissance, mais aussi la plus faible survie. Les experiences sur la photoperiode donnent une meilleure croissance pour une photop&iode de 18 heures et une meilleure survie pour une photophriode de 12 heures. La combinaison photop&iode-intensit6 lumineuse confirme l’hypoth&e que les fortes intensitGes lumineuses sont lethales pour les larves juste &closes (non pigmentees). L’eclairage doit @tre rCduit (700 lux) durant la premiere semaine; par la suite, une lumitire continue (2,000 lux) favorise la survie et une photop&iode de 14 6 16 heures ameliore la croissance.
REFERENCES Alderson, R. and Bromley, P.J., 1973. A method for rearing larvae of the turbot, Scophthalmus maximus L., to metamorphosis. ICES, CM/E: 20, 11 pp. Alessio, G., 1975. Riproduzione articiale di orata, Sparus aurata (L.) (Osteichthyes, Sparidae) 5’-Primi risultati sull’allevamento ed alimentazione delle larva et degli avanotti. Boll. Pesca, :?iscic. Idrobiol., 30(l): 71-92. Alessio, G., Gandolfi, G. and Scheiber, B., 1976. Induction de ponte, Clevage et alimentation des larves et des alevins des poissons euryhalins. CGPM, FAO, Etudes et Revues, 55: 14.3-158. Ballon, E.K., 1975. Terminology of the intervals in fish development. J. Fish. Res. Board Can., 32(9): 1663-1670. Barahona-Fernandes, M.H., 1978a. Effect of aeration on the survival and growth of sea bass (Cticentrurchus Zabrax) larvae: a preliminary study. Aquaculture, 14: 67-74. Barahona-Fernandes, M.H., 197813. Croissance et survie des larves de bar (Dicentrarchus labrax (L.)) en fonction de la date de ponte et des lots de gGniteurs, en conditions de laboratoire. ICES, CM/G: 54, 12 pp. Barahona-Fernandes, M.H., 1978c. L’Blevage intensif des larves et des juveniles du bar (Dicen !rarchus labrax (L.)): don&es biologiques, zootechniques et pathologiques. ThBse d’l&at de 1’UniversitG d’Aix-Marseille II, 208 pp., reneo. Barahona-Fernandes, M.H. and Girin, M., 1977. Effect of different food levels on the growth and survival of the laboratory reared sea-bass larvae (Dicentrarchus Zabrax (L.)). 3rd Meeting of the ICES Working Group on Mariculture, Actes de Colloques du CNEXO, 4: 69-84.
320 Barnabe, G., 1976. Contribution a la connaissance de la biologie du loup Dicentrarchus labrux (Poisson Serranidae). These de l’universite de Montpellier, 228 pp., reneo. Blaxter, J.H.S., 1968. Rearing herring larvae to metamorphosis and beyond. J. Mar. Biol. Assoc. U.K., 48: 17-28. Blaxter, J.H.S., 1973. Monotoring the vertical movements and light responses of herring and plaice larvae. J. Mar. Biol. Assoc. U.K., 53: 635-647. Bromley, P.J., 1977. Methods of weaning juvenile hatchery reared sole (Solea solea L.) from live to prepared diets. Aquaculture, 12: 337-347. Fliichter, J., 1974. Laboratory rearing of the common sole (Solea solea L.) under controlled conditions of high density with low mortality. In: J.H.S. Blaxter (Editor), The Early Life History of Fish. Springer Verlag, Berlin, pp. 725-730. Fuchs, J., 1978. Influence de la photoperiode sur la croissance et la survie de la larve et de juvenile de sole, Solea solea, en Blevage. Aquaculture, 15: 63-74. Gabriel, M.L., 1944. Factors affecting the number and the form of vertebrae in Fund&s heteroclitus. J. Exp. Zool., 95: 105-147. Girin, M., Barahona-Fernandes, M.H. and Le Roux, A., 1975. Larval rearing of sea-bass (Dicentrarchus Zabrax (L.)) with high survival. ICES, CM/G: 19, 8 pp. Gross, W.L., Roelofs, E.W. and Fromm, P.O., 1965. Influence of the photoperiod on growth of green sunfish, Lepomis cyanellus. J. Fish. Res. Board Can., 22: 1379-1386. Houde, E.D., 1973. Some recent advances and unsolved problems in the culture of marine fish larvae. Proc. World Mar. Sot., 3: 83-103. Houde, E.D., 1976. Critical food levels from growth and survival of laboratory reared larvae of three species of sub-tropical marine fishes. ICES, CM/E: 50, 23 pp. Houde, E.D. and Palko, B.J., 1970. Laboratory rearing of the clupeid fish Harengula pensacolae from fertilized eggs. Mar. Biol., 5: 354-358. Howell, B.R., 1973. Marine Fish Culture in Britain. VII-A marine rotifer, Brachionus plicatilis Miiller, and the larvae of the mussel, Mytilus edulis L., as foods for larval flatfish. J. Cons. Int. Explor. Mer, 35(l): 1-6. Htun-Han, H., 1977. The effects of photoperiod on reproduction in fishes. An annoted bibliography. MAAF Directorate of Fisheries Research, Library Information Leaflet, 6: 30 pp. Huh, H.T., Cabbert, H.E. and Sturiber, P.A., 1976. Effects of temperature and light on growth of yellow perch of Wallaye using formulated feed. Trans. Am. Fish. Sot., 2: 254-272. Lasker, R., 1976. The relation between oceanographic conditions and the larval anchovy food in the California current: identification of factors contributing to recruitment failure. ICES, CM/L: 35, 38 pp. Lasker, R., Feder, H.M., Theilacker, G.H. and May, C.M., 1970. Feeding, growth and survival of Engraulis mordax larvae reared in the laboratory. Mar. Biol., 5: 345-353. Laurence, G.C., 1976. A bioenergetic model for the analysis of feeding and survival of winter flounder larvae (Pseudopleuronectes americanus) during the period from hatching to metamorphosis. ICES, CM/L: 36, 44 pp. Nash, C.E., Kuo, C.M. and McConnel, S.C., 1974. The grey mullet: operational procedures for rearing. Oceanic Inst., Waimanalo, Hawaii, Tech. Rep., O&-73-128: 23-28. O’Connell, C.P. and Raymond, L.P., 1970. The effect of food density on survival and growth of the northern anchovy (Engraulis mordax Girard) in the laboratory. J. Exp. Mar. Biol. Ecol., 5: 187-191. Ramos, J., 1977. Primeras experiencias de cria de1 linguado (Solea solea L.). Informes Tecnicos de1 Inst. Inves. Pesq., 48: l-16. Reynolds, W.W. and Thomson, D.A., 1974. Responses of young gulf grunion Leurestes sardina to gradients of temperature, light, turbulence and oxygen. Copeia, 3: 747-758. Riley, J.D., 1966. Marine fish culture in Britain. VII-Plaice (Pleuronectes platessa L.) postlarval feeding on Artemia saline L., nauplii and the effects of varying feeding levels. J. Cons. Perm. Int. Explor. Mer, 30(2): 204-221.
321 Riley, J.D. and Thacker, G.T., 1963. Marine fish culture in Britain. III-Plaice (t-‘leurorructes platesso (L.)) rearing in closed circulation at Lowestoft, 1961. J. Perm. Int. Bxpl. Mer, 28: 80--90. Rosenthal, H. and Hempel, G., 1970. Experimental studies in feeding and f’ooa reyuirements of herring larvae (Clupeia harengus L.). In: J.H. Steele (Editor), Marme Food Chains. Univ. Calif. Press, Berkley, Calif., pp. 344-364. Ryland, J.S., 1966. Observations on the development of larvae oi tne pialce, ~feuror~ecrrs platessc! L. in aquaria. J. Cons. Perm. Int. Explor. Mer, 3U(2): 177-195. Saville, A., 1971. The larval stage. CIEM, Rapp. P.V. Reunions, 160, Syrnp,uslum on the Biology of the Early Stages and Recruitment Mechanisms of Herrmg, pp. 52-55. Spectorova, L.V., Aronovich, TM., Donoshov, 8.1. and Poova, V.P., 1974. Artificial rearing of the Black Sea turbot larvae (Scophthalmus rnueoticus). Aquaculture, 1: 329-3,20. Stepien, W.P., 1976. Feeding of the laboratory-reared larvae of the sea bream Arcnusu~-gcrs rhomboidalis (Sparidae). Mar. Biol., 38: l-6. Struhsaker, J., Hashimoto, D.Y., Girard, S.M., Prior, F.T. and Cooney, T.D., 1973. Effect of antibiotics on survival of carangid fish larvae (Caranx mate) reared in the lauolatury. Aquaculture, 2: 53-88. Villani, P., 1976. Ponte induite et Clevage des larves de poissons marlns dans des conditiuns de labaratoire. CGPM, FAO, fitudes et Revues, 55: 117-132.
Amsterdam
-
Printed
in The Netherlands
313
SOME EFFECTS OF LIGHT INTENSITY AND PHOTOPERIOD ON THE SEA BASS LARVAE (DICENTRARCHUS LABRAX (L.)) REARED AT THE CENTRE OCEANOLOGIQUE DE BRETAGNE
MARIA
HELENA
Faculdade Contribution (Accepted
BARAHONA-FERNANDES
de Cicncias, no. 625 1 March
Departamento
de Zoologia,
du Ddpartement
Scientifique
Lisbon
(Portugal)
du Centre
Oceanologique
de Bretagne
1979)
ABSTRACT Barahona-Fernandes, M.H., 1979. Some effects of light intensity and photoperiod sea bass larvae (Dicentrarchus labrax (L.)) reared at the Centre Oceanologique Bretagne. Aquaculture, 17: 311-321.
on the de
Four experiments were performed to determine the effects of light intensity on the growth and survival of sea bass larvae; two experiments dealt with the photoperiod and two with the combined effects of light intensity and the photoperiod. Recently hatched larvae from the same spawning were used within each experiment. The light intensity experiments show that there is better growth but poorer survival at higher light intensities. The photoperiod experiments show a better growth at 18 h photoperiod and a better survival at 12 h exposure to light. The study of the combined effects of light intensity and photoperiod confirmed the hypothesis that strong light intensities are lethal to newly hatched larvae (with no pigmentation). If the light intensity is lowered during the first week, the best rearing conditions were found to be continuous lighting relative to survival rate, and 14-16 h photoperiod relative to growth.
INTRODI’CTION
It is wlell known that marine fish larvae are positively phototropic and that feeding is greatly facilitated by a high light intensity, in accordance with the importance of vision to particulate planktonophagic fishes. In the rearing systems studied, all authors used bright light which was above the general threshold at first feeding, above l-10 lux (Blaxter, 1968). Alessio (1975) found no differences in the results of Sparus auruta larvae reared from 300 to 10,000 lux. Riley and Thacker (1963) and Houde and Palko (1970) had a poorer survival at the lower light intensity with Pleuronectes platessa and Harengula pensacolae, but did not give the light intensities used. The searching volume of Clupea harengus per day was not affected by changes in light intensity from 10 to 1,000 lux (Rosenthal and Hempel, 1971). Blaxter (1968,1!373), Houde and Palko (1970), Houde (1973,1976) and Stepien
312
(1976) found that fish larvae are incapable of eating in complete darkness. The possible effect of the photoperiod on the growth of fish larvae is not often considered as an independent controlling factor, although its role int the reproductive cycles has been extensively studied (Htun-Han, 1977). Huh et al. (1976) studied the growth rates of Perca fluvescens and concluded that they were nearly three times greater with 16 h light than with only 8 h. Gross et al. (1965) found that the growth and the food conversion efficiency of Lepomis cyanellus were higher with 16 h than 8 h of light. Nevertheless, most of the authors use continuous light for rearing marine fish larvae (O’Connell and Raymond, 1970; Struhsaker et al., 1973; Fliichter, 1974; Spectorova et al., 1974; Barnabe, 1976; Villani, 1976; Ramos, 1977). Others use different photoperiods, from 10 to 16 h light, without any explanation about their choice (Riley, 1966; Ryland, 1966; Blaxter, 1968; Lasker et al., 1970; Rosenthal and Hempel, 1970; Alderson and Bromley, 1973; Howell, 1973; Alessio, 1975; Girin et al., 1975; Alessio et al., 1976; Houde, 1976; Laurence, 1976; Stepien, 1976; Bromley, 1977). This paper is a study of the effects of changing the light intensity and the photoperiod on sea bass larvae in reference to their growth, survival and condition coefficient. MATERIAL
AND METHODS
The general rearing schema was the same as described by Barahona-Fernandes (1978a,b,c) and Fuchs (1978). Four experiments were performed to determine the effects of light intensity, two on the effects of the photoperiod and two on the combined effects of light intensity and photoperiod. The water in the tanks was thermoregulated at 19 i 1°C and the oxygen level was kept between 88 and 110% (5.73 ml/l and 6.69 ml/l). The water flow increased up to 40 l/h in the 150 1 tanks and up to 20 l/h in the 60 1 tanks. The rearing tanks were cylindroconical, 150 1 capacity for the light intensity and 60 1 capacity for the photoperiod studies. All rearing tanks were lighted by two 20 watt “Grolux” fluorescent tubes (day light type) suspended 30 cm above the tank surface and giving light intensity at the water surface from 1,400 to 3,500 lux during the night, and 2,000 to 3,500 lux during the day. These differences were due to the natural daylight coming through the room windows. The desired changes in the light intensity were obtained by sticking black PVC sheet covering to different areas of the lamps. The photoperiod experiments were made in a series of three 60 1 tanks, one under continuous lighting and two enclosed in wooden boxes with their lamps connected to a time clock giving 18 and 12 h light periods (from 1 a.m. to 7 p.m. and from 7 a.m. to 7 p.m. respectively). In all experiments on light intensity effects, one tank was under strong light intensity (1,400-3,500 lux) and a second one received light filtered through the plastic PVC, from which the light intensities indicated in Table I
313 TABLE
I
Initial larval number confidence intervals
and density, percentage for 95% in the different
Experiment
of survival, experiments
condition coefficient with the on light intensity effects
Initial larval density and larval number
Final survival
.._______ 1,400--3,500 lux tank 303700 lux tank
42 larvae/l (6,300 1)
19.8% 23.4%
Final condition coefficient --0.44 + 0.03 0.29 !C0.03
II
1,403-3,500 lux tank 303700 lux tank
60 larvae/l (9,000 1)
6.3% 16.9%
0.39 f 0.03 0.38 f 0.02
III
1,403-3,500 lux tank 303- 1000 lux tank
60 larvae/l (9,000 1)
10.3% 16.1%
0.42 + 0.02 0.37 * 0.01
IV
1,403-3,500 lux tank 1513-- 800 lux tank
60 larvae/l (9,000 1)
8.6% 21.2%
0.47 t 0.01 0.40 + 0.05
I
resulted. In the photoperiod experiments, one tank was also under continuous strong light intensity (1,400-3,500 lux) and the other two tanks, enclosed in the wooden boxes, had total darkness during the dark periods and 2,0003,500 lux during the light periods. In the experiments on the combined effects of light intensity and photoperiod, these last installations were used, but during the first 7 days the light intensity was reduced in all tanks to :5
4
f
A
Fig. 1. Growth curves of the larvae in the four experiments effect, with the mean values and their confidence intervals intensity tank; (-) lower light intensity tank.
A
performed on light intensity for 95%. (- - -) high light
314
800-1,000 lux. At 7 days, the larvae are already pigmented and the light intensity can then be increased. The initial density of larvae in the tanks varied from 43 to 70 per liter and, within each experiment, they were from the same spawning. The larvae used in Expt. I on the effects of light intensity and the ones used in Expt. a in the photoperiod effects were from the same spawning. Every 10 days, a sample of 10 fish was removed from each tank and preserved in 5% neutralized formalin for later measurements and weighing. Every day the tanks were cleaned of the detritus accumulated at the bottom. The feeding schema was the same as described by Barahona-Fernandes and Girin (1977). Brachionus plicatilis was given from day 3 to day 15, reaching a maximum of 7.5 prey/ml; Artemia salina nauplii were distributed from day 10 onwards, reaching a maximum of 0.1-2 prey/ml. All these amounts correspond to the estimated necessary feeding needs for 24 h. RESULTS
The growth curves with the mean values of the samples and their 95% intervals of confidence for the light intensity effect9 are shown in Fig. 1. The analysis of variance highlights the significantly better growth of the larvae under strong light intensities: in Expt. I, F,,l, = 42.13**; in Expt. II, F,,,, = 5.69**; in Expt. III, F1,18 = 11.33**; and in Expt. IV, Fills = 9.66”“. Table I gives the initial number of larvae and the final survival, both as percentage and in number of survivors, and the condition coefficients with their 95% confidence intervals. It is clear that the best survival were always obtained at lower light intensities and that the best final condition coefficients were always obtained at higher light intensities. The growth curves for the two experiments performed on the photoperiod effects are shown in Fig. 2 with the mean values of the samples and with their 95% confidence intervals. The analysis of varience with orthogonal breakdown revealed that the significant differences between the treatments are due to the better final growth of the larvae at 18 h light (Expt. a, F,,26 = 28.28”, and Expt. b, F,,,, = 4.45’). The initial larvae number, the final survival and the final condition coefficient with their confidence intervals for 95% are given in Table II for the photoperiod experiments. The best survival was obtained at 12 h and the highest final condition coefficient at 18 h light. As the larvae used in Expt. I on the light intensity effects and those used in Expt. a on the photoperiod effects were from the same spawning, it was possible to compare the growth in the same light and photoperiod conditions (continuous 1,400-3,500 lux) in the 150 1 and 60 1 tanks. Although the mean weight of the larvae at 30 days in the 150 1 tank was 10.09 mg and in the 60 1 tank 8.36 mg, the analysis of variance showed no significant differences (F I,18 = 0.503). From the same spawning, the optimum growth was also compared in 150 1 tanks (24 h light at 2,000-3,500 lux) to the optimum growth in the 60 1
315 WET
WEIGHT
(mg )
A
A
32-
28 -’
69
24.
20-
Fig. 2. Grcwth curves of the larvae in the two experiments performed on the photoperiod effects, with the mean values and their confidence intervals for 95%; (-) 24 h light photoperiod; (- - -) 18 h light photoperiod; (- - - - -) 12 h light photoperiod.
tank (18 h light at 2,000-3,500 lux). The mean wet weight in the first case was 10.09 mg and in the second 12.45 mg at 30 days. The analysis of variance did not show significant differences (F1,18 = 1.02). The final survival was better in the 150 1 tanks than in the 60 1 tanks. TABLE
II
Initial larval number and density in the tanks, final survival percentage, and condition coefficient with the confidence intervals for 95% in the different experiments on photoperiod effects .~~~_~.___ Experiment ___a 24 h tank 18 h tank 12 h tank b
24 h tank 18 h tank 12htank
Initial
Final survival
larvae
Final condition coefficient
_ 70 larvae/l (4,200 1)
70 larvae/l (4,200 1)
4.6% 3.8% 9.2%
0.37 0.44 0.37
* 0.05 5 0.03 r 0.04
22.5% 24.2% 51.4%
0.42 0.48 0.37
* 0.06 + 0.03 + 0.02
_
316
The results of t,he t~wo experiment,s performed on the combined effects of the light intensity, and the photoperiod are given in Table III. All tanks contained 3.000 larvae in the beginning of the experiments. The orthogonal breakdown of the total F shows that the growt.h rates at 14 and 16 h light are not significantly different from each other, but are significantly higher than growth under 18 and 24 h light regimes. DISCUSSION
The effects of increasing the light intensity during the rearing period are clear: in all experiments the final growth and the condition coefficients were significantly bet,ter. In natural conditions, the sea bass juvenile is a diurnal feeding fish and increasing the light intensity facilitates the vision and the preving ability; the enhanced feeding ability on the growth rate of fish larvae is obvious (Reynolds and Thomson, 1974). The results of final survival in the light intensity experiments show that fish in two of the experiments had a similar final survival, both at the higher and the lower light intensity; in the other two experiments, the final survival was clewlv lower at higher light intensity. The effects of the photoperiod on the growth during the rearing period are also clear. In both experiments, the best growth was obtained at 18 h light photonerind. The same photoperiod also resulted in higher condition coefficimt,a. An improved growth can also be obtained by increasing the day length art,ificiallv, provided ihere is no physiological upset due to photoperiod or lack of it (Rlaxter, 1968). Fuchs (1978) obtained a better growth of sole larvae under the same conditions with 12 h light but with no difference in the final survival r&es. In the experiments on the combined effects of the photoperiod and the light intensity better survival was obtained under continuous lighting, and b&er growth and condition coefficients at 14 and 16 h light. The best light intensit,v for rearing marine fish larvae varies according to the species. Ales~io (1975) had the same rearing results for gilthead sea bream between 300 and 10.000 lux; with the sea bass larvae reared under a light intensity up to 1.000 liix, significantly poorer growth is obtained than under 2,000 to 3.500 11~~.Riley and Thacker (1963) and Houde and Palko (1970) found lnw~r SV-viva1 in the less illuminated tanks. In t.he experiments reported here, on the light intensity and photoperiod effects only, the best growth has been obtained under continuous and strong light and the hest final survival under 12 h of Lwer light intensity. One possihle explanation for these results was put forward by Alessio (1975), Gabriel (1944) and Nash et al. (1974): strong light intensities before the total pigmentation of the larvae (from eleutheroembryo to pterygiolarvae, according to Rallon (1975)) would be lethal to the fish larvae. It is generally accepted that the larval mortality occurs at the eleutheroembryo stage; it seems logical that the lower light intensities or the shorter periods under strong light in-
Experiment 2
Experiment 1
Final survival (%) 37.1
0.40 ? 0.03
Final condition coefficient
f 2.6
4.2
Final growth (mg)
13.6
0.38 i 0.02
Final condition coefficient
Final survival (%)
7.3
Final growth (mg) ? 3.4
i 3.1
0.9
-
-
0.38 + 0.03
7.8 + 6.3
4.3
-
-
-
0.42 + 0.03
13.5
f 4.1 -r 5.4
i 2.2
8.4
0.44 + 0.03
7.2
0.41 + 0.02
14.3 11.1
-
Fills= 3.93"
F Ill8 = 20.17”
F,,,,= 4.52”
F 4/4s = 5.73”
Results of the experiments on the combined effects of light intensity and photoperiod with the final values of growth, condition coefficient and survival percentage, along with the confidence intervals for 95% and the results of the analysis of variance for the growth and condition coefficient parameters Photoperiod 16 14 24 18 F test (hours light)
TABLE III
318
tensity would therefore decrease the mortality. Results of the experiments reported here seem to be in accordance with this hypothesis. The results of the experiments on the combined effects of the light intensity and the photoperiod show clearly that these two parameters cannot be studied separately and confirm that a strong light intensity before the total pigmentation of the larvae induces a high mortality. It is always difficult to compare laboratory results with natural conditions, but Saville (1971) observed that recently hatched larvae stay close to the sea bottom except when a marked mixing occurs down to the bottom; also, after this stage, in daylight, the larvae have their major distribution in mid-water and upwards. These field observations seem to be in agreement with the results reported in this paper. Once the factor that screened the real effects of the photoperiod is found and eliminated, it becomes clear that the sea bass larvae have a significantly better growth under the photoperiod to the geographic limits of the species (36”N to 50”N, i.e., areas from 9 h 43 min to 14 h 30 min - 36”N - and from 8 h 03 min to 16 h 18 min - 50”N); but the best survival is obtained under continuous lighting. Alderson and Bromley (1973), Lasker (1976) and Laurence (1976) proved the low predatory capacity of the young larval stages. Under continuous lighting the chances of meeting prey-larvae increase; the risks of under feeding decrease. The importance of this last factor on the larval survival is well known (Houde, 1973). But the growth is somewhat affected by forcing the larvae to remain active beyond the time they would be under natural environmental conditions. The comparison of the growth capacities of each spawning confirms that, in the same rearing conditions, they are significantly different (BarahonaFernandes, 197810). In the experiments reported here, the mean wet weights of the larvae at 30 days varied from 4.26 to 10.38 mg. The increase of the larval growth, within each spawning, obtained by changing the rearing conditions into the most favourable ones, can balance the annual fluctuations between the growth capacity of the different spawnings. CONCLUSION
The present work shows that light intensity and photoperiod studies cannot be performed separately. If the light intensities are constant, the photoperiod studies would lead to the choice of the 18 h photoperiod for the best growth and the 12 h photoperiod for the best final survival results. If the light intensity is lower during the first 7 days after hatching (period of progressive pigmentation of the larvae), then the best final survival is obtained under continuous lighting, and the best growth with a photoperiod of 14 to 16 h. Further studies should be carried out in order to determine the optimal pattern of light intensity and photoperiod for sea bass larvae.
319
ACKNOWLEDGEMENTS
The author acknowledges a fellowship from the French Government through the Frenlsh Embassy in Lisbon, and also wishes to thank A. and L. Laubier and M. Girin for the critical reading of the manuscript, and G. Hekinian for his help.
Barahona-Fernandes, M.H., 1979. Quelques aspects des effets de 1’intensitC lummeuse et de la photopCriode sur les larves du bar (Dicentrarchus la brax (L. )) BlevCes au Centre Ockanologique de Bretagne. Aquaculture, 17: 311-321 (en anglais). Huit es.p&iences ont CtC menees sur les effets de la lumiere sur la croissance et la survie des larves de bar de l’&losion B 1 mois: quatre exp&iences sur 1’intensitC lumineuse, deux exp&iencc:s sur la photoperiode et deux expGriences sur l’action cornbinGe de l’intensite lumineuse et de la photop&iode. Dans chaque expgrience, des larves issues de la mdme ponte ont BtB utilis8es. Les plus fortes intensites lumineuses donnent la meilleure croissance, mais aussi la plus faible survie. Les experiences sur la photoperiode donnent une meilleure croissance pour une photop&iode de 18 heures et une meilleure survie pour une photophriode de 12 heures. La combinaison photop&iode-intensit6 lumineuse confirme l’hypoth&e que les fortes intensitGes lumineuses sont lethales pour les larves juste &closes (non pigmentees). L’eclairage doit @tre rCduit (700 lux) durant la premiere semaine; par la suite, une lumitire continue (2,000 lux) favorise la survie et une photop&iode de 14 6 16 heures ameliore la croissance.
REFERENCES Alderson, R. and Bromley, P.J., 1973. A method for rearing larvae of the turbot, Scophthalmus maximus L., to metamorphosis. ICES, CM/E: 20, 11 pp. Alessio, G., 1975. Riproduzione articiale di orata, Sparus aurata (L.) (Osteichthyes, Sparidae) 5’-Primi risultati sull’allevamento ed alimentazione delle larva et degli avanotti. Boll. Pesca, :?iscic. Idrobiol., 30(l): 71-92. Alessio, G., Gandolfi, G. and Scheiber, B., 1976. Induction de ponte, Clevage et alimentation des larves et des alevins des poissons euryhalins. CGPM, FAO, Etudes et Revues, 55: 14.3-158. Ballon, E.K., 1975. Terminology of the intervals in fish development. J. Fish. Res. Board Can., 32(9): 1663-1670. Barahona-Fernandes, M.H., 1978a. Effect of aeration on the survival and growth of sea bass (Cticentrurchus Zabrax) larvae: a preliminary study. Aquaculture, 14: 67-74. Barahona-Fernandes, M.H., 197813. Croissance et survie des larves de bar (Dicentrarchus labrax (L.)) en fonction de la date de ponte et des lots de gGniteurs, en conditions de laboratoire. ICES, CM/G: 54, 12 pp. Barahona-Fernandes, M.H., 1978c. L’Blevage intensif des larves et des juveniles du bar (Dicen !rarchus labrax (L.)): don&es biologiques, zootechniques et pathologiques. ThBse d’l&at de 1’UniversitG d’Aix-Marseille II, 208 pp., reneo. Barahona-Fernandes, M.H. and Girin, M., 1977. Effect of different food levels on the growth and survival of the laboratory reared sea-bass larvae (Dicentrarchus Zabrax (L.)). 3rd Meeting of the ICES Working Group on Mariculture, Actes de Colloques du CNEXO, 4: 69-84.
320 Barnabe, G., 1976. Contribution a la connaissance de la biologie du loup Dicentrarchus labrux (Poisson Serranidae). These de l’universite de Montpellier, 228 pp., reneo. Blaxter, J.H.S., 1968. Rearing herring larvae to metamorphosis and beyond. J. Mar. Biol. Assoc. U.K., 48: 17-28. Blaxter, J.H.S., 1973. Monotoring the vertical movements and light responses of herring and plaice larvae. J. Mar. Biol. Assoc. U.K., 53: 635-647. Bromley, P.J., 1977. Methods of weaning juvenile hatchery reared sole (Solea solea L.) from live to prepared diets. Aquaculture, 12: 337-347. Fliichter, J., 1974. Laboratory rearing of the common sole (Solea solea L.) under controlled conditions of high density with low mortality. In: J.H.S. Blaxter (Editor), The Early Life History of Fish. Springer Verlag, Berlin, pp. 725-730. Fuchs, J., 1978. Influence de la photoperiode sur la croissance et la survie de la larve et de juvenile de sole, Solea solea, en Blevage. Aquaculture, 15: 63-74. Gabriel, M.L., 1944. Factors affecting the number and the form of vertebrae in Fund&s heteroclitus. J. Exp. Zool., 95: 105-147. Girin, M., Barahona-Fernandes, M.H. and Le Roux, A., 1975. Larval rearing of sea-bass (Dicentrarchus Zabrax (L.)) with high survival. ICES, CM/G: 19, 8 pp. Gross, W.L., Roelofs, E.W. and Fromm, P.O., 1965. Influence of the photoperiod on growth of green sunfish, Lepomis cyanellus. J. Fish. Res. Board Can., 22: 1379-1386. Houde, E.D., 1973. Some recent advances and unsolved problems in the culture of marine fish larvae. Proc. World Mar. Sot., 3: 83-103. Houde, E.D., 1976. Critical food levels from growth and survival of laboratory reared larvae of three species of sub-tropical marine fishes. ICES, CM/E: 50, 23 pp. Houde, E.D. and Palko, B.J., 1970. Laboratory rearing of the clupeid fish Harengula pensacolae from fertilized eggs. Mar. Biol., 5: 354-358. Howell, B.R., 1973. Marine Fish Culture in Britain. VII-A marine rotifer, Brachionus plicatilis Miiller, and the larvae of the mussel, Mytilus edulis L., as foods for larval flatfish. J. Cons. Int. Explor. Mer, 35(l): 1-6. Htun-Han, H., 1977. The effects of photoperiod on reproduction in fishes. An annoted bibliography. MAAF Directorate of Fisheries Research, Library Information Leaflet, 6: 30 pp. Huh, H.T., Cabbert, H.E. and Sturiber, P.A., 1976. Effects of temperature and light on growth of yellow perch of Wallaye using formulated feed. Trans. Am. Fish. Sot., 2: 254-272. Lasker, R., 1976. The relation between oceanographic conditions and the larval anchovy food in the California current: identification of factors contributing to recruitment failure. ICES, CM/L: 35, 38 pp. Lasker, R., Feder, H.M., Theilacker, G.H. and May, C.M., 1970. Feeding, growth and survival of Engraulis mordax larvae reared in the laboratory. Mar. Biol., 5: 345-353. Laurence, G.C., 1976. A bioenergetic model for the analysis of feeding and survival of winter flounder larvae (Pseudopleuronectes americanus) during the period from hatching to metamorphosis. ICES, CM/L: 36, 44 pp. Nash, C.E., Kuo, C.M. and McConnel, S.C., 1974. The grey mullet: operational procedures for rearing. Oceanic Inst., Waimanalo, Hawaii, Tech. Rep., O&-73-128: 23-28. O’Connell, C.P. and Raymond, L.P., 1970. The effect of food density on survival and growth of the northern anchovy (Engraulis mordax Girard) in the laboratory. J. Exp. Mar. Biol. Ecol., 5: 187-191. Ramos, J., 1977. Primeras experiencias de cria de1 linguado (Solea solea L.). Informes Tecnicos de1 Inst. Inves. Pesq., 48: l-16. Reynolds, W.W. and Thomson, D.A., 1974. Responses of young gulf grunion Leurestes sardina to gradients of temperature, light, turbulence and oxygen. Copeia, 3: 747-758. Riley, J.D., 1966. Marine fish culture in Britain. VII-Plaice (Pleuronectes platessa L.) postlarval feeding on Artemia saline L., nauplii and the effects of varying feeding levels. J. Cons. Perm. Int. Explor. Mer, 30(2): 204-221.
321 Riley, J.D. and Thacker, G.T., 1963. Marine fish culture in Britain. III-Plaice (t-‘leurorructes platesso (L.)) rearing in closed circulation at Lowestoft, 1961. J. Perm. Int. Bxpl. Mer, 28: 80--90. Rosenthal, H. and Hempel, G., 1970. Experimental studies in feeding and f’ooa reyuirements of herring larvae (Clupeia harengus L.). In: J.H. Steele (Editor), Marme Food Chains. Univ. Calif. Press, Berkley, Calif., pp. 344-364. Ryland, J.S., 1966. Observations on the development of larvae oi tne pialce, ~feuror~ecrrs platessc! L. in aquaria. J. Cons. Perm. Int. Explor. Mer, 3U(2): 177-195. Saville, A., 1971. The larval stage. CIEM, Rapp. P.V. Reunions, 160, Syrnp,uslum on the Biology of the Early Stages and Recruitment Mechanisms of Herrmg, pp. 52-55. Spectorova, L.V., Aronovich, TM., Donoshov, 8.1. and Poova, V.P., 1974. Artificial rearing of the Black Sea turbot larvae (Scophthalmus rnueoticus). Aquaculture, 1: 329-3,20. Stepien, W.P., 1976. Feeding of the laboratory-reared larvae of the sea bream Arcnusu~-gcrs rhomboidalis (Sparidae). Mar. Biol., 38: l-6. Struhsaker, J., Hashimoto, D.Y., Girard, S.M., Prior, F.T. and Cooney, T.D., 1973. Effect of antibiotics on survival of carangid fish larvae (Caranx mate) reared in the lauolatury. Aquaculture, 2: 53-88. Villani, P., 1976. Ponte induite et Clevage des larves de poissons marlns dans des conditiuns de labaratoire. CGPM, FAO, fitudes et Revues, 55: 117-132.