Experimental analyses on the effect of the larval growth rate to the predation mortality of small pelagic fishes

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INTRODUCTION Growth rates of fish larvae represent survival potential during these stages, playing a key role in survival dynamics. The paradigm that faster-growing individuals are more likely to survive has emerged through numerous studies, and led to various field study designs, although there have been some conflicting observations. Anderson(1988) concluded that the theory linking growth rate and mortality provides a rational framework, but that the relationship remains to be quantified. To clarify how growth rates regulate survival, experimental analyses were conducted to demonstrate the relationships between environmental and biological factors, including growth rate and nutritional condition, and swimming activity which highly related to the escape ability from the predation risks. Two major approaches were adopted in our study.1) Measurement of the endurance speed of young Japanese anchovy Young fishes of Japanese anchovy, Engraulis japonicus, were used for measuring of 60 minut … More es endurance speed in a water tunnel(100 cm long x 30 cm depth x 30 cm width) at a temperature of 17-27℃. Elapsed time from start of swimming were measured individually and biological parameters(body length, body weight, visceral weight and weight of stomach content) were measured after the experiments. Endurance time changed depending on temperature and several biological parameters, and decreased according with the increase of specific speed in body length.2) Sampling instrument for selecting fishes in the different school positions A sampling instrument for selecting fishes in the different school positions was designed. The selecting sampling instrument was built and attached in the water tunnel mentioned above. More than ten times sampling trials were done on the young fishes of Japanese anchovy. Fast, middle and slow group of young fishes in each school were sampled at the same time. Results of otolith analyses indicated no clear relationships between the larval growth rate and the position in the school. Less