Basic studies on the culture of pejerrey. II. Effects of temperature upon survival and histological changes of starved pejerrey Odontesthes bonariensis larvae.

Preliminary results on the effects of incubation and rearing temperatures on histological and morphometrical features and on starvation induced mortality of first feeding pejerrey larvae are presented. Newly hatched larvae at 17.5°C were nearly 8% larger than those at 21.5°C, had significantly larger lower jaw lengths and mouth gapes but smaller yolk reserves owing to the longer incubation periods. The differences decreased with growth, but still favored larvae at lower temperatures. Larvae hatched at 19.5°C had intermediate length and availalbe energy, but relatively larger oil globules. Energy consumption and growth rates were directly proportional to temperature at both pre and post hatching periods. Yolk conversion efficiencies were initially similar and later maximal at 19.5°C. Yolk and oil were never completely absorbed in starved and dying larvae. Mortality of larvae starved throughout amounted to 50% at 5.5, 7.1 and 7.3 days respectively at 21.5, 19.5 and 17.5°C, but total mortality varied little from an average of 9 days irrespective of temperature. Survival in the delayed feeding trials decreased with longer starvation periods at 21.5 and 19.5°C. Such a trend could not be clearly identified at 17.5°C until total mortality. Histological criteria developed in an earlier study were employed to analyze the dynamics of changes and loss of tissue integrity and their correlation with survival expectancy. Initial changes were slower at 19.5°C, but leveled at days 3 and 4. After 4 and 5 days of starvation, the percentages of larvae bearing similar pancreatic and intestinal degeneration were similar, but liver seemed to be least affected at 17.5°C. It becomes evident that temperature interacts with starvation to affect potential survival and that utilization of histological methods to assess starvation induced mortalities should take temperature into consideration.