Concentration of 17α-Methyltestosterone in HormoneTreated Feed: Effects of Analytical Technique, Fabrication, and Storage Temperature

Feed treated with 17α-methyltestosterone (MT) is used to manipulate the gender of early tilapia fry. In the USA, hormone-treated feed is used by selected producers under an Investigational New Animal Drug (INAD) program. While monitoring the fabrication and on-farm use of this treated feed, concerns were raised about the high performance liquid chromatography (HPLC) analytical procedure for detecting MT in feeds, the incorporation of MT in feeds during fabrication, and effects of storage temperature on MT concentration. A series of experiments demonstrated that the analytical procedure for detecting MT in feeds lacked high precision, and, on average, biased results low. MT was uniformly mixed with feed by spraying an MT-alcohol solution on feed while it was blended in an industrial ribbon mixer. Alcohol volumes ranging from 15 mL/kg to 150 mL/kg were equally effective at dispersing MT in feed. The concentrations of MT in feeds consistently declined over time if the storage temperatures were 25 C or higher. Freezing preserved the MT in feed, and the refrigeration of feed fabricated to contain 60 mg MT/kg maintained acceptable MT concentrations during 6 mo of storage.     

'Broken-Skull Disease' in African Catfish Clarias gariepinus is Related to a Dietary Deficiency of Ascorbic Acid

Abstract.— Diets containing 0. 23, 46, 69, 92, and 185 mg ascorbic acid/kg of diet were fed to African catfish Clarias gariepinus juveniles (average initial weight, 19.9 g) for 20 wk in glass aquaria. Fish fed diets supplemented with 0 or 23 mg ascorbic acid/kg showed overt signs of broken-skull disease, such as hemorrhages along the spinal column and inflammation of dorsal skull bone followed by broken skull and death. They also had significantly lower vertebral collagen content and had significantly higher mortality than fish fed 46 mg or more ascorbic acid/kg of diet. Results from this study indicate that a dietary deficiency of ascorbic acid can cause broken-skull disease and high mortality in African catfish. A concentration of 46 mg ascorbic acid/kg of diet will prevent this anomaly and allow optimum synthesis of vertebral collagen.     

Phosphorus Budgets for Channel Catfish Ponds Receiving Diets with Different Phosphorus Concentrations

Phosphorus budgets were prepared for channel catfish Ictalurus punctatus ponds at Auburn, Alabama, that received one of five diets ranging from 0.60 to 1.03% phosphorus. Fish production did not differ ( P > 0.05) among diets. There were few differences among treatments with respect to soluble reactive phosphorus, total phosphorus, and chlorophyll a concentrations or gross primary productivity. Phosphorus loss in effluents when ponds were drained for harvest did not differ among treatments ( P > 0.05). Phosphorus removed from ponds in fish at harvest and the amounts of phosphorus adsorbed by bottom soils increased as dietary phosphorus concentration increased (P < 0.05). Low-phosphorus diets did not decrease phytoplankton productivity or improve effluent quality. Uptake of phosphorus by bottom soils is a major factor controlling phosphorus concentrations in pond water. Low-phosphorus diets can be beneficial in catfish pond management by reducing the phosphorus load to bottom soils and conserving their ability to adsorb phosphorus.     

Net Absorption of Dietary Phosphorus from Various Inorganic Sources and Effect of Fungal Phytase on Net Absorption of Plant Phosphorus by Channel Catfish Ictalurus punctatus

Year-2 channel catfish (average weight 765 g) were fed a commercial-type, all-plant diet containing supplemental phosphorus (0.40%) from one of various sources, or fungal phytase (1,000 and 3,000 units), in 1-m³ circular raceways for 21 d at a temperature of 28–30 C. Subsequently, net absorption of phosphorus from the diets was determined by the chromic oxide indicator method in which feces were collected from the rectum. Net absorption of the supplemental phosphorus was corrected for the absorbed residual phosphorus in the basal diet. Net absorption coefficients for monosodium phosphate, monoammonium phosphate, finely ground defluorinated rock phosphate and monocalcium phosphate were 88.6, 85.4, 81.7, and 81.2%, respectively, and were not significantly different. Net absorption coefficient for dicalcium phosphate was significantly lower, 74.8%, but was significantly higher than those for coarsely ground defluorinated rock phosphate and tricalcium phosphate, which were 55.1 and 54.8%, respectively. These data are in general agreement with relative bioavailability values based on growth response for channel catfish determined in other research, and should be appropriate for determining available phosphorus allowances in commercial feeds and establishing phosphorus budgets in aquaculture feeding operations. The net absorption of phosphorus from the all-plant basal diet was 31.2% and increased significantly to 55.1 and 62.5% with the addition of 1,000 and 3,000 units of fungal phytase, respectively.