UBC Theses and Dissertations
Influence of incubation salinity and temperature and post-hatching temperature on salinity tolerance of Pacific herring (Clupea pallasi Valenciennes) larvae Dueñas, Corazon Echevarria
A study was conducted to determine the effects of incubation salinity and temperature . and post-hatching temperature on salinity tolerance of Pacific herring (Clupea pallasi Valenciennes) larvae. Calorimetry experiments were also conducted on herring larvae that were incubated and reared in various combinations of salinity and temperature. In the salinity tolerance test, herring eggs were artificially fertilized in three salinities (13, 21 and 29°/ooS) at 6°C. Newly fertilized eggs were incubated in the same salinities as those in which they were fertilized at two levels of incubation temperature (6 and 12°C), making six incubation groups. During the peak of the hatching period, groups of larvae from each incubation group were exposed to a series of test salinities, ranging from 20 to 55°/ooS at three levels of post-hatching temperatures (6, 9 and 12°C). Salinity tolerance was measured by determining the mortality of larvae occurring in each test salinity over a period of 72 hours. Two approaches were employed: 1) time-mortality, and 2) dosage-mortality. The former provided estimates of the effective time to 50% mortality (ET₅₀), the latter, the effective dosage (salinity) to 50% mortality (ED₅₀). The ET₅₀ or ED₅₀ values were used as bases for comparison of the responses of larvae to incubation temperature and salinity, and post-hatching temperature. The results indicate that both incubation salinity and temperature exert a significant influence on the salinity tolerance of larvae. Eggs incubated in the highest salinity (29°/ooS) and lower temperature (6°C) produced larvae most tolerant to higher post-hatching salinities. Post-hatching temperature also showed a possible influence, although the trends seen were not statistically significant. Salinity tolerance of larvae hatching from the 6°C incubation temperature appeared to be maximized at post-hatching temperatures between 6 and 9°C; whereas, those larvae from the 12°C incubation temperature showed maximum salinity tolerance at 9 to 12°C post-hatching temperatures. The response. of. larvae to salinity may be a result of an irreversible non-genetic adaptation of the embryo to salinity and temperature during incubation. In the calorimetry experiments, samples of herring larvae were combusted in a microbomb calorimeter to determine caloric values. These larvae were hatched and reared in the same six combinations of incubation salinities and temperatures as those used in the main experiment. Larvae were sampled at day 0 (peak of hatching), 3, 6 and 9. Standard lengths, dry weights, ash-free dry weights and ash content of the larval samples were also taken. There was a considerable variability in the data for calorimetry of the herring larva. In general, larvae from all treatments, at hatching, averaged 6,586 cal/g ash-free dry weight and had a mean ash value of 8.25%, obtained by direct ashing. Mean standard length of larvae at the peak of hatching (day 0) ranged from 7.67 mm (12°C, 29°/ooS) to 9.93 mm (6°C, 13°/ooS). There was a trend towards larger larvae (greater standard length) at lower temperatures in lower salinities in all ages tested. Data on dry weights show a linear decrease in larval (body and yolk) weight from day 0 to day 9. Mean dry weight of larva at the peak of hatching ranged from 0.142 mg (6°C, 13°/OOS) to 0.162 mg (12°C, 21°/ooS; 12°C, 29°/ooS). At day 0, the largest larvae (in terms of dry weight) were found at higher temperatures in higher salinities, while at day 9 (past yolk-sac stage), the largest larvae were found at lower temperatures in lower salinities. The same trend was observed in terms of ash-free dry weight.
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