Growth and Bone Development in Channel Catfish Fed 17-α-Methyltestosterone in Production Ponds

Effects of feeding 17-α-methyltestosterone (MT) to channel catfish ( Icralurus punctatus ) grown to harvestable size in earthen ponds were examined. Channel catfish fingerlings (mean weight, 14.4 g), stocked in 0.04 ha ponds (7,410 fish/ha) were fed diets containing MT at concentrations of 0, 2.5, and 10 mg/kg for 123 days. Weight gain by fish fed the control diet (0 MT) was higher ( P < 0.05) than that of fish fed the treated diets. Increasing the dietary concentration of MT reduced weight gain further ( P < 0.05). Both male and female fish fed MT had enlarged and thickened heads, and their skins were dark. Their dorsal and pectoral spines were short and the tips, which are normally very sharp, were soft and blunt. Weight of the rib bones per unit of length decreased ( P < 0.05) as MT was added to the diet. Breaking strength of the ribs (force required to break the bone at its midpoint) measured by an Instron shear press, was less ( P < 0.05) for fish fed MT than for control fish. The ratio of calcium to phosphorus in bones was lower ( P < 0.05) in fish fed MT. These results indicate that feeding MT at these doses (2.5 mg/kg or above) to channel catfish suppresses growth rate and reduces size and strength of bones.