Effects of salinity on eggs and yolk-sac larvae of Atlantic cod, Atlantic halibut, haddock and winter flounder

Powell, Frank (1998) Effects of salinity on eggs and yolk-sac larvae of Atlantic cod, Atlantic halibut, haddock and winter flounder. Masters thesis, Memorial University of Newfoundland.

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Abstract

Recent interest in the culture of cold water marine fish has prompted many questions with regards to water quality during early culture. Although temperature is probably the most important parameter of water quality, another key factor in determining site locations as well as optimizing success is salinity. Since salinity may vary dramatically from one location (e.g. estuarine) to another (eg. open ocean), determination of the optimal salinity for a species is important in selecting site locations for prospective marine hatcheries. The current study investigated salinity effects in four prospective aquaculture species: winter flounder, haddock, cod, and halibut. -- Studies were undertaken to determine the optimal salinities for egg survival and their effects on the viability, size, and behaviour of newly-hatched larvae. Eggs from each species were incubated at salinities of 15, 20, 25, 30, and 35 ppt and a variety of parameters including hatch rate, % viable larvae, larval size, yolk volume and hatching problems were measured. In addition, overall larval condition was assessed using a temperature stress test and cell cleavage patterns among haddock and halibut eggs were investigated as indicators of larval viability. -- Halibut eggs failed to develop past blastopore closure when incubated in salinities of 25 ppt or less, resulting in 0% hatch rates. Eggs incubated at 30 and 35 ppt demonstrated significantly higher hatch rates and there were no noticeable differences in early larval success at these two salinities. -- Among haddock embryos, hatch and viability rates were found to be high at all salinities tested, although there was a slight decrease at 15 ppt. Haddock larval length and yolk size was found to be significantly greater if eggs were incubated at lower salinities. Larvae expressed greater tolerance to temperature shock if eggs had been incubated at lower salinities. -- Cod eggs hatched successfully at all salinities although larval viability was better above 25 ppt, being maximal at 35 ppt. Larval size was generally unaffected by salinity although yolk area was significantly larger at lower salinities. Temperature stress tests revealed greater larval tolerance if eggs had been incubated at higher salinities. -- Winter flounder embryos displayed significantly higher hatch and viability rates if incubated at 15-20 ppt compared to 30 and 35 ppt Larval length tended to be maximal at the mid salinities (25 ppt) while as seen in the other species, yolk area was largest at 15 and 20 ppt Larvae subjected to temperature stress survived significantly longer if eggs had been incubated at 15 ppt. -- Early egg cleavage patterns (symmetrical vs. asymmetrical) were not found to be reliable indicators of larval viability in either halibut or haddock eggs.

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