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Notes: Juvenile channel catfish were fed purified diets supplemented with magnesium (Mg) from Mg sulfate at levels of 0, 200, 400, 600, 800, and 1,000 mg/kg and 0, 200, 400, 600, and 800 mg/kg in two separate feeding studies. In study I, the effect of dietary levels of Mg on growth response, vertebral mineral content, and macrophage chemotaxis were evaluated. Study II had similar objectives except that whole body mineral content was measured, and resistance of channel catfish to Edwardsiella ictaluri challenge was also determined. Fish with an average weight of 10.89 g were stocked at a rate of 50 fish/110-L aquarium (study I). In study II, fish with an average weight of 4.14 g were stocked at rates of 40 fish/110-L aquarium. Prior to stocking, each batch of fish was acclimated to laboratory conditions and fed the basal diet for 2 wk. The concentration of Mg in rearing water was 1.8 mg/L. Each diet was fed to fish in quadruplicate and triplicate aquaria to apparent satiation for 10 wk for studies I and II, respectively. Fish fed the basal diet started to die as early as 3 d after the study began (17 d of feeding the diet without Mg supplementation). In both studies, weight gain, survival, and feed efficiency were lowest for fish fed the basal diet but increased with increasing dietary levels of Mg. However, the differences between the values of each of these parameters for fish fed diets containing supplemental Mg were not always significant. Magnesium-deficiency signs observed were anorexia, sluggishness, convulsions, deformed snout, vertebral curvature, muscle flaccidity, and high mortality. Vertebral and whole body ash concentrations were high, but Mg content was low for fish fed the basal and the 200-mg Mg diets. Bone Ca content did not differ among fish fed different diets (study I), but whole body Ca tended to increase for fish fed the basal diet, suggesting the possibility of calcification of soft tissues. Macrophage chemotaxis in the presence of exoantigen was highest for fish fed diets supplemented with Mg at 400 and 200 mgkg for studies I and II, respectively. When expressed in terms of chemotaxis index, however, maximum or near maximum value was observed at a dietary Mg level of 400 mg/kg. Thus, a dietary level of Mg of 400 mg/kg from Mg sulfate was required for optimum growth and survival, maintaining high tissue levels of Mg, prevention of muscle flaccidity and skeletal deformity, and stimulating macrophage chemotaxis. Dietary levels of Mg had no effect on the resistance of juvenile channel catfish to Edwarsiella. ictaluri challenge.

Notes: Solvent-extracted cottonseed meal was used in shrimp Penaeus vannamei diets at levels of 0, 13.3, 26.5, 39.8, 53.0 and 66.3%, substituting on an equal nitrogen basis for 0, 20, 40, 60, 80 and 100% of animal protein mix (53% menhaden fish meal, 34% shrimp waste meal and 13% squid meal). The feeds were formulated to contain 32% crude protein and 3,100 kcal metabolizable energy/kg. Each diet was fed to juvenile shrimp to satiation four times daily for 8 wk. Shrimp fed the three lowest dietary levels of cottonseed meal (0, 13.3 and 26.5%) had similar weight gain, feed consumption and survival. The performance of shrimp was adversely affected when diets containing more than 26.5% cottonseed meal, or 1,100 ppm free gossypol, were fed. Shrimp fed the diet with 39.8% cottonseed meal or 1,600 ppm free gossypol had depressed weight gain, reduced feed intake and high mortality. The groups receiving the two highest dietary levels of cottonseed meal lost weight by the end of week 4 and all shrimp in these treatments died within 6 to 8 wk. These adverse effects were probably due to the toxicity of free gossypol. Shrimp appeared to accumulate gossypol in the body as evidenced by light yellow-green coloration in shrimp fed diets containing cottonseed meal.

Notes: The dietary iron requirement for normal growth and optimum hematological values and bioavailability was determined for channel catfish Ictalurus punctatus fingerlings using egg-white based diets supplemented with 0,5,10,20,60, and 180-mg iron/kg from iron methionine or 20, 60, and 180-mg iron/kg from iron sulfate. The basal diet which contained 9.2-mg iron/kg, 34% crude protein and 3.1 kcal of digestible energy/g was fed to channel catfish fingerlings (8.5 g) in triplicate flow-through aquariums to satiation twice daily for 8 wk. Fish fed the basal diet without iron supplementation exhibited poor growth throughout the 8-wk period. Fish fed iron-supplemented diets did not differ with regard to final weight gain. Survival, feed conversion, total blood cell count, mean corpuscular hemoglobin concentration, serum iron, total iron binding capacity, and transferrin saturation were not significantly affected by dietary iron level. Hemoglobin, hematocrit, mean corpuscular hemoglobin, and mean corpuscular volume were significantly lower in fish fed the basal diet. These values were also consistently lower for fish fed diets with 5 and 10-mg iron/kg from iron methionine. However, differences were not always significant. Results of this study indicate that supplementation of 5-mg iron from iron methionine was sufficient for growth. However, a supplemental iron level of 20-mg/kg diet or a total iron level of 30-mg/kg of diet appeared to be needed for optimum hematological values. Iron methionine and iron sulfate were equally effective in preventing anemia in channel catfish.

Notes: Red hybrid tilapia Oreochromis mossambicus×O. niloticus fingerlings were fed diets containing 0, 2.5, 5.0, 10.0, 20.0 and 40.0 mg/kg, and 0, 2.5, 5.0, 7.5, 10.0 and 20.0 mg/kg of riboflavin in separate 8 and 12 wk feeding studies, respectively. The dietary riboflavin level required to provide maximum growth and survival, and prevent deficiency symptoms in red hybrid tilapia fingerlings was found to be approximately 5 mg/kg of diet. In both trials, fish fed the diet devoid of supplemental riboflavin exhibited anorexia, reduced growth and nervous symptoms after 4–6 wk. Mortality began to occur after the sixth week. None of these abnormalities were observed during the first 6 wk in fish fed the riboflavin supplemented diets. However, by the seventh week, fish fed the diet supplemented with 2.5 mg/kg of riboflavin showed reduced appetite and growth rate. In both experiments, short body dwarfism was observed during week 8 for fish fed the diet without riboflavin supplementation. In experiment 1, fish fed the riboflavin-deficient diet had lens cataracts at week 8. This deficiency sign was not observed in experiment 2. Histological studies of liver, kidney, spleen, lateral muscle, gill and gastrointestinal tract revealed no major histopathological changes.

Notes: Channel catfish Ictalurus punctatus fingerlings were fed purified diets supplemented with iron at levels of 0, 20, 60, and 180 mg/kg from iron sulfate (FeS) or 5, 10, 20, 60, and 180 mg/kg from iron methionine (FeM) in triplicate tanks for 8 wk. Fish were then divided into two groups and subjected to different assays to measure disease resistance and individual immune functions. Representative fish from each dietary treatment were challenged by bacterial immersion with virulent Edwardsiella ictaluri, and mortality due to enteric septicemia was recorded. Other fish were immunized with 0.2–mL formalin-killed E. ictaluri and boosted 21 d post-immunization. Antibody response was determined by FAST-ELISA. Chemiluminescent and chemotaxis assays were performed using peritoneal macrophages. Supplementation of the diet with various levels of iron from FeS or FeM did not significantly affect antibody production. Chemotactic migration by macrophages was depressed in iron-deficient fish and a level of 60 mgkg from either FeS or FeM provided the highest chemotactic indexes. A deficiency of dietary iron was found to increase mortality of channel caffish due to enteric septicemia of catfish (ESC). However, more studies should be conducted to better understand the effects of sources and levels of dietary iron on immune responses and disease resistance in channel caffish.