Preliminary report on the effects of temperature on the development of eggs and larvae of halibut (Hippoglossus hippoglossus) and on the bacterial population in the incubators

Eggs were stripped from one female of the halibut broodstock at Austevoll Aquaculture Station, and fertilised with sperm from two males immediately before incubation. Eggs were held in nine open-circulation 250 l incubators at either 3°, 6° or 9°C with three incubators at each temperature. When hatched, the larvae were transferred to fifteen similar incubators, with five incubators at each temperature. The timing of developmental events in the eggs and larvae was monitored, mortality in the egg and larval stages recorded, growth and yolk absorbtion measured in the larvae, RNA and DNA content and RNA/DNA ratios determined for each temperature group and samples taken for embryonal and larval histology. Total and viable count of free-living bacteria in the incubators was monitored from hatching until termination of the experiment. Flow rate, temperature, oxygen and ammonia were recorded. Differences in development rates were apparent from the first cell divisions. The mean number of Kuppfer's vesicles was most in the 9°C groups and least in the 6°C groups. At hatching, relative protein synthesis and yolk sac size was best at 3°C but there was no difference in standard length between the groups. At 9°C, larvae grew faster, but developed abnormalities associated with sublethal stressors. A rise in mortalities occurred at the same stage of development at 6° and 9°C. An increase in larval mortalities lead to an increase in bacteria which preceded an increase in ammonia levels. There was no significant difference in bacterial numbers between groups. The experiment was terminated due to uncontrolled temperature fluctuations