Extensive research on the early life history of tropical tunas has been developed by the IATTC at the Achotines Laboratory in the Republic of Panama over 30 years. Larval feeding research encompassing prey selectivity, effect of different light levels on growth and survival, and analysis of diel feeding patterns of reared yellowfin tuna (YFT) larvae are described in the present study. Two experiments were conducted providing mixed prey assemblages at different concentrations during the early larval stages to analyze prey selectivity and the onset of piscivory in YFT larvae. Analyses on prey concentration, prey width, larval mouth width and larval growth were conducted. Pearre’s C index was calculated to describe selection of major prey items by YFT larvae during development. Results suggest YFT larvae are selective feeders, having different preferences in accordance with size and food concentration, and the early onset of piscivory could be observed and described.
The effect on growth and survival of YFT larvae was analyzed under three different light intensities (low, medium, and high). Light intensity treatments were replicated in multiple tanks, and larval growth, survival and gut content were examined during the first 10 days of feeding. Survival rates were higher in the high light level treatment. Prey consumption during initial days of feeding was highest under the high and medium light levels. However, in the last days of the experiment, the differences in prey consumption among treatments were not statistically significant. These results are consistent with the visual developmental characteristics of YFT larvae.
Lastly, two experiments were conducted to analyze the diel feeding patterns in YFT larvae at first feeding, flexion, and post-flexion stage. The mean number of prey per larval gut and percentage of empty guts were analyzed under diel cycles during the three developmental phases of the larvae. Results suggest that YFT larvae are diurnal feeders but with the ability to hunt and feed in relatively low light conditions.
Feeding habits in the early life stages are a crucial aspect of the feeding ecology and larval nutrition, and a critical process for the early survival of YFT tuna larvae. Hence, information on food habits, preferences, and feeding responses for different environmental cues are an important aspect of the research conducted on early life history of YFT larvae.