Size-related differences in growth and survival in piscivorous fish larvae fed different prey types

• This study examines larval fish responses to planktivorous and piscivorous diets.
• Experiments were conducted on two species, Atlantic bluefin tuna and Atlantic bonito.
• The timing of transition to a piscivorous diet is critical for growth and survival.
• Results have implications for the culture, ecology and conservation of apex predators.

The switch from a planktivorous to a piscivorous diet is critical to survival in many fishes. In this study we examine the development of foraging and physiological capabilities in relation to planktivorous and piscivorous diets in larval fish. Specifically, we manipulated the timing of onset of piscivory and recorded its consequences for size, growth, and survival in Atlantic bluefin tuna (Thunnus thynnus) and bonito larvae (Sarda sarda) reared under experimental laboratory conditions. Our results show that an early transition to piscivory benefits survival and increased growth during the larval stage, when food abundance is not limiting for both species. For bluefin tuna, high survival rates could only be maintained when fish larvae were included in the diet. For bonito, survival rates significantly decreased over a six-day period if the addition of fish larvae was delayed by three days. These results are important for the study of the development of successful juvenile production systems and reveal an important element for recruitment success of bluefin tuna and bonito in the field.