EXPERIMENTAL SEA-WATER SYSTEMS 

 FOR REARING FISH LARVAE 



By J. E. Shelbourne, Fishery Research Biologist 



Ministry oF Agriculture, Fisheries, and Food Fisheries Laboratory, Lowestoft, Suffolk, England 



Abstract. — Marine fish are not easj to rear in aquariums, but encouraging results 

 have been achieved for tlie plaice {Plcurnnectes platessa) in closed circulation at Lowe- 

 stoft. Two temperature-controlled sea-water systems are described, both using illumi- 

 nated green algae for metabolite regulation, and one having a measure of bacterial 

 control by ultraviolet light. Survival is better in open circulation where metabolite 

 accumulations are less severe. Two further hatchery systems are outlined ; one deliver- 

 ing a continuous flow of filtered and temperature-adjusted sea water for local experi- 

 mental use, and the other for conducting long-term experiments on chemical factors 

 affecting egg and larval survival. 



U.S. Fisheries Commissioner Spencer 

 F. Baird (1880) pioneered the first at- 

 tempt to rehabilitate a depleted sea fishery 

 by large-scale artificial propagation in ma- 

 rine hatcheries. His efforts were influ- 

 enced by the discovery of G. O. Sars 

 (1866) that a cod egg conld be artificially 

 fertilized in much the same way as a fresh- 

 water fish egg. The American example 

 stimulated European interest; hatcheries 

 were soon erected in Norway and Britain, 

 but after several decades of operational 

 use, with no solid returns, hatchery prac- 

 tice fell into disrepute. Technical devel- 

 opment became stunted by the inability 

 of pioneers to rear sea fish in large num- 

 bers beyond their tender early stages. 

 Production was measured in terms of eggs 

 and early larvae liberated into the sea, 

 rather than tough fish with reasonable 

 chances of further survival. 



Even in those early days, certain species 

 had been reared through the postlarval 

 phase, including the herring (Meyer, 

 1880), the cod (Rognerud, 1887), the 

 plaice (Dannevig, 1897), the sole (Fabre- 

 Domergue and Bietrix, 1905) and the tur- 



bot (Anthony, 1910), but all on an experi- 

 mental scale. Mass production in quanti- 

 ties sufficient to influence the yield of a 

 fishery still remains a fish culturist's 

 dream. Work towards this end began at 

 Lowestoft in 1957, the main aim being to 

 develop a small-scale technique which 

 could guarantee a consistent annual target 

 production of metamorphosed plaice 

 {Pleuronectes platessa) from sea-spawned 

 eggs. By 1960, up to 10-percent survival 

 had been achieved in closed circulation; 

 this was increased to 33 percent during 

 1961 in open circulation at Port Erin, Isle 

 of Man, giving survivor densities of 166 

 fish per square foot of tank bottom. 



So far, our technique has developed in 

 an empirical fashion — making mistakes 

 and learning to avoid them. Now that a 

 satisfactory procedure has been worked 

 out, it will be possible to start a more sys- 

 tematic study of factors affecting larval 

 survival, with a reasonable expectation of 

 positive results. This information will 

 help us to streamline oiir technique and 

 to approach the problem of mass produc- 

 tion with economy of effort. Complete 



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