Dietary Zinc and Cobalt Requirements of Fry of Seabass (Lates calcarifer) and Catfish (Clarias batrachus)

An 8-week experiment was conducted to determine the cobalt and zinc requirements of fry of seabass (Lates calcarifer) and catfish (Clarias batrachus). Fifteen diets for each fish were formulated with varying concentrations of cobalt and zinc, alone and in combination. The control diet was not supplemented with cobalt or zinc. The diets for L. calcarifer had 45% protein, while the diets for C. batrachus had 30%. The diet that produced the best growth for L. calcarifer (1100%) contained 2.5 mg Co + 45 mg Zn/kg diet and for C. batrachus (1149%) contained 5 mg Co + 30 mg Zn/kg. Growth in the control L. calcarifer was 738% and in the control C. batrachus was 428%. For both species, the food conversion ratios were best in the above diets, 1.17±0.52 for L. calcarifer and 1.40±0.62 for C. batrachus as opposed to 1.89±0.39 and 2.54±0.61 for the respective controls

Effects of Selected Levels of Water pH on the Growth and Survival of Swordtail (Xiphophorus helleri) Larvae

Larvae of swordtail (Xiphophorus helleri) were exposed to pH levels of 5.5, 6.0, 7.0, 8.0, and 8.5 to study growth and survival under laboratory conditions for 42 days. The larvae were fed formulated dry pellets at 7% of their body weight. The growth and survival rates were highest at pH 8.0 and 8.5, while mortality was complete at pH 5.5. In all treatments, the specific growth rate was higher in the first week and decreased in subsequent weeks. Thus, for swordtail larvae, the pH of the water should be between 8.0 and 8.5