Determination of the optimal water temperature for the culture of juvenile dusky kob Argyrosomus japonicus Temminck and Schlegel 1843

The effects of temperature on growth, food-conversion ratio (FCR) and feeding intensity of juvenile dusky kob Argyrosomus japonicus (23.7 +/- 2.6 g fish(-1)) were assessed over the temperature range 17.5-28.5 degrees C in a 42-day growth trial. Growth increased with increasing temperature up to an optimum after which it declined. Specific growth rates were 2.05% and 1.2% day(-1) for the fastest (25.3 degrees C) and the slowest (17.5 degrees C) treatments respectively. Food-conversion ratio peaked at a lower temperature than growth. Optimal (0.72 kg kg gain(-1)) and least efficient (1.40 kg kg gain(-1)) FCR were found at 21.7 and 17.5 degrees C respectively. Feeding intensity was linearly related to temperature within the range of 17.5-28.5 degrees C. These results corresponded to the thermal preference (25-26.4 degrees C) and natural temperature distribution (12-28 degrees C) of South African dusky kob. Determination of the temperature range that does not limit growth is a prerequisite to assess the relationship between growth and environmental variables such as light intensity, feeding regime and stocking density. Consequently, experiments to determine the effects of these environmental variables on growth and aquaculture potential of dusky kob should be conducted at 24-26 degrees C.