Effects of temperature, recent feeding history, and fish size on the otolith size - fish size relationship

Accurate back-calculation of larval fish growth relies on the premise that there is a constant proportionality between otolith size and fish size for the period studied. Although this relationship is generally accepted, the otolith size—fish size relationship can become decoupled under some circumstances. The objectives of this study were to quantify the role of temperature, recent feeding history, and fish size in regulating the otolith size—fish size relationship for larval tilapia. Eggs or yolk-sac larvae were obtained from adult tilapia maintained in 1,500-L recirculation systems in the Clemson University Aquatic Animal Research Laboratory. Eggs were hatched and larvae raised to either a small (9 mm total length) or large (12 mm) size for use in experiments. Experiments involving feed manipulation and fish size were conducted at nominal temperatures of 23°C and 28°C. This design resulted in four treatment groups per temperature: large-fed, large-starved, small-fed, and small-starved. Experiments lasted 9 days and fish that received the starvation treatment were only starved between days 0 and 3. Fed fish reared at the high temperature were over three fold larger in weight and over 50% larger in length than starved fish at the end of the study period. No change in length or weight of starved fish over the starvation period was detected. However, condition values of starved fish were lower at the end of the starvation period than at the beginning. Starved fish had greater water content than fed fish at the end of the starvation period. Lipid levels of starved fish were lower than those of fed fish by the end of the starvation period, while protein levels were greater for starved fish. The effect of starvation was exaggerated at the higher temperature due to increased metabolic demands. Otolith size was an accurate predictor of fish size for all treatment groups. A difference in regression parameters between fed and starved fish within temperature and size groups could not be detected, except between low-temperature, small, fed and starved fish. Fish reared at the high temperature had larger otoliths than similar sized fish reared at the low temperature. The otolith size—fish size relationship does not appear to have a consistent response to starvation and temperature changes.