The endogenous nutrition period of fish larvae is considered critical for the early life stage of fishes. During the transition from endogenous nutrition to exogenous feeding, many fish larvae fail to initiate successful first feeding, which may lead to starvation, adverse growth, abnormal behavior even mortality. Swimming performance is an important parameter indicating the potential survival ability of many fish species due to its ecological relevance in animals’ predator avoidance and hunting success. However, limited information is available on the effect of the timing of first feeding on the swimming performance in fish larvae, and its relationship to energy content and body length.
Southern catfish (Silurus meridionalis Chen) is widely distributed in the Yangtze and Zhujiang Rivers, where the food abundance experiences drastic seasonal fluctuation. Spawning in the early spring, the first feeding in larvae southern catfish coincide with one of the most unstable periods in terms of food availability. We suspect the plasticity of the timing of first feed in this species may be one of the keys to its success in its natural habitat. The current study is to swimming performance as an indicator to illustrate how energy content and body length.
The effect of the timing of initial feeding (4, 5, 6 and 7 days post-hatch, dph) on energy content, body size and swimming performance of artificially fertilized southern catfish larvae were conducted at (22.0 ± 0.5)℃ in the Laboratory of Evolutionary Physiology and Behavior of Chongqing Normal University. Larvae were sampled and analyzed for energy content, body weight and length measurement before feeding at 4dph, and different delayed first feeding treatment at 7dph and 21dph. The critical swimming speed (Ucrit) of larvae with different delayed first feeding treatment were also measured at 7 dph and 21 dph. The parameter measured at 7dph showed that the energy content, body weight and body length of larvae had a tendency to decrease with increased delayed first feeding time whereas no significant difference in Ucrit was found among different experimental groups. The relative critical swimming speed was increased with first feeding time increase from 4 to 6 dph, and decreased with first feeding time increased from 6 to 7 dph. The data at 21 dph showed that the body weight, energy content and body length of larvae first fed at 5, 6 and 7 dph gradually approach those of larvae first fed at 4 dph. The effect of delayed first feeding had most impact on energy content specific growth rate (SGR_E％), then on the body length specific growth rate (SGR_L％), whereas it had the least impact on the absolute critical swimming speed among the three parameters. The results indicated that in Silurus meridionalis Chen, the swimming performance was less plastic while the body energy content was more plastic compared with the body length when facing the temporal fluctuation of food availability during the early development stage.