FlSHfRY BULI FTIN: VOL. 72. NO. 2 



ence of antibiotics) and SO^c survival (eggs irri- 

 gated with seawater free of antibiotics during in- 

 cubation). 



Despite the lower larval survival rate when fed 

 artificial food it is felt that this rate is sufficiently 

 high to demonstrate the technical feasibility of 

 using non-living food for rearing marine fish lar- 

 vae. Moreover, eggs are produced in enormous 

 numbers by marine fish and are extremely cheap 

 so that a 209r survival rate to metamorphosis is an 

 acceptable level. If such a survival rate can be 

 achieved with the more exacting larvae of highly 

 esteemed species (Dover sole, turbot) it would give 

 a considerable impetus to the cultivation of these 

 fish. 



DISCUSSION 



Reviewing marine fish larval rearing, May 

 (1970) named the provision of a suitable food (i.e. 

 "one which the larvae will consume and grow on 

 and which can be supplied in sufficiently large 

 quantities") as the prime obstacle. Several at- 

 tempts have been made over the years to rear 

 marine fish larvae on non-living, composite foods 

 but none of these have yet been successful (Fishel- 

 son, 1963; Blaxter, 1962; Ivanchenko and Ivan- 

 chenko, 1969). In practice we have had no great 

 difficulty in getting plaice larvae or at least a 

 relatively high proportion of them to ingest the 

 food and develop on it. The main obstacle has been 

 one of tank hygiene and it remains the overriding 

 problem. This too is recognized by May ( 1970) who 

 comments on the use of non-living food: "un- 

 eaten food accumulates on the bottom of the rear- 

 ing container and decays rapidly, fouling the 

 water". Although the present set-up does permit 

 control of the quantity of uneaten food in the 

 water, any improvements in tank design which 

 release uneaten food completely while retaining 

 the larvae are desirable. Various modifications of 

 tank design to this end are under consideration. 

 The problem is particularly acute in the early 

 stages as the food particles tend to swell in the 

 water and fail to pass the screen at the bottom of 

 tank. As larvae increase in size, and a screen of 

 larger mesh size can be substituted at the bottom 

 of the tank, the problem becomes less acute. 



Some bacteriological control of water may be 

 attained by sterilizing the incoming water by 

 means of ultraviolet light and such a device should 

 be incorporated into future experiments. 



Microencapsulation of the food may offer a 

 further means of improving tank hygiene. The 

 microcapsules currently available seem to sink 

 very rapidly through a water column. This mili- 

 tates against their chances of being consumed by 

 larval fish in a rearing tank. The development of 

 neutrally buoyant microcapsules, however, could 

 lead to rapid strides in the controlled cultivation of 

 larval marine fish. 



The use of an antibiotic in the diet calls for some 

 comment. The relatively free use in animal feeds 

 of those antibiotics which are commonly employed 

 in human medicine has obvious social dangers. 

 Attention has yet again been focused on these 

 dangers by Williams-Smith ( 1973). It must, there- 

 fore, be emphasized that furanace was used in 

 very low concentrations and that it has been de- 

 veloped specifically for use in fish. Thus any resis- 

 tant strains which could result from its use should 

 still be sensitive to antibiotics currently in use in 

 clinical medicine. 



The diet used was designed empirically with the 

 objects of providing a relatively large intake of 

 high quality protein, marine oil, and a luxus of B 

 vitamins all allied to reasonable water stability. 

 The diet is by no means ideal and there is clearly 

 scope for improvement in this ration in many 

 ways. However, it does provide a basic experimen- 

 tal formula from which more nearly optimal diets 

 may evolve. 



LITERATURE CITED 



Adron, J. W. 



1972. A design for automatic and demand feeders for ex- 

 perimental fish. J. Cons. 34:300-305. 

 Blaxter, J. H. S. 



1962. Herring rearing-IV. Rearing beyond the yolk-sac 

 stage. Mar. Res. Dep. Agric. Fish. Scotl. 1, 18 p. 



BOOKHOUT, C. G.,AND J. D. COSTLOW, Jr. 



1970. Nutritional effects of Artemia from different loca- 

 tions on larval development of crabs. Helgolander Wiss. 

 Meeresunters. 20:435-442. 

 CowEY, C. B., J. A. Pope, J. W. Adron, and A. Blair. 



1972. Studies on the nutrition of marine flatfish. The pro- 

 tein requirement of plaice (Pleuronectes platessa). Br. J. 

 Nutr. 28:447-456. 



FiSHELSON, L. 



1963. Observations on littoral fishes of Israel. II. Larval 

 development and metamorphosis oi Blennius pavo Risso 

 (Teleostei, Blenniidae). Isr. J. Zool. 12:81-91. 



Ivanchenko, L. A., and O. F. Ivanchenko. 



1969. Transition to active feeding by larval and juvenile 

 white sea herring (Clupea harengus pallasi NATIO 

 Maris-albi BERG) in artificial conditions. Dokl. Akad. 

 Nauk SSSR 184:1444-1446. 



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