Growth and mortality of zebra fish, Brachydanio rerio (Hamilton Buchanan), maintained at two temperatures and on two diets

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Abstract
One hundred zebra fish per tank were maintained for 112 days at 24°C or 28°C in glass aquaria and fed a diet of flaked food made without cellulose (13.45 kJ g−1, metabolizable energy, Type A) or with cellulose (8.71 kJ g−1, metabolizable energy, Type B). Each experimental condition was repeated in triplicate (12 tanks). The weight of food given daily to the fish was based on daily records of survivors (from which mortality rates were calculated) and wet wt of fish (measured every 14 days) in each tank. All fish were fed with the same weight of food per day and the quantity of energy in the food in excess of standard metabolism (as a proportion of SM) was approximately 0–5 for fish maintained at 28°C and fed food B, 1–0 for fish maintained at 24°C and fed food B, 1–5 for fish maintained at 28°C and fed food A, and 2.2 for fish maintained at 24°C and fed food A.Non‐ionized ammonia, nitrite and nitrate nitrogen in the tanks did not reach toxic levels although there was an increase in total ammonium nitrogen in one tank and a subsequent heavy mortality. It was assumed that this was caused by the build up of pathogenic bacteria. Apart from this tank, mortality was highest in tanks at 28°C with fish fed food A and second highest in tanks at 24°C with fish fed on the same diet. Growth was measured in units of length, wet and dry weights, carbon and energy. There was a good correlation (P < 0.001) between carbon (mgC mg−1) and calorific (J mg−1) values and a conversion factor of 46.2 J (mgC)−1 was derived. Fish maintained at 24°C and fed food A had the highest rates of growth both in weight and in energy value per unit weight. Fish fed the same diet but kept at 28°C had the lowest growth rates. Both these groups of fish had the highest coefficients of variation in wet weights which increased during the experiment, indicating an increase in interaction within the tanks. There was agreement between the energy value of fish sampled for growth and a condition factor based on the length‐weight relationships of fish remaining in the tanks. A correlation (P < 0.05) was found between instantaneous mortality and growth rates for fish between tanks when those maintained at 28°C and fed on food A were ignored.