Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/9/2002
Publication Date: 3/12/2003
Citation: Lim, C.E., Klesius, P.H. 2003. Influence of dietary levels of magnesium on growth, tissue mineral content and resistance of channel catfish (Ictalurus punctatus) challenged with Edwardsiella ictaluri. Journal of the World Aquaculture Society. 34:18-28. Interpretive Summary: Magnesium(Mg) requirements for growth and prevention of deficiency symptoms have been determined for several fish species including channel catfish. Magnesium has also been shown to affect the host immunological systems and defense mechanisms in warm-blooded animals. However, no studies have evaluated the effect of dietary levels of Mg on the response of channel catfish. Thus, this study was conducted to evaluate the effect of dietary levels of Mg on growth performance, tissue mineral content, hematology, immunity and resistance of catfish to Edwardsiella ictaluri challenge. Results obtained from two separate feeding studies showed that fish fed Mg deficient diet had anorexia, poor growth and feed efficiency ratio, muscle flaccidity, sluggishness, convulsive seizure, skeletal deformity, low tissue Mg concentrations, and increased mortality. Bone and whole body Mg were more sensitive than growth response parameters in evaluating the adequacy of dietary Mg. Total cell count, red blood cell count, hematocri and hemoglobin were not affected by dietary levels of Mg. A dietary supplemental level of 400mg Mg from Mg sulfate/kg diet was optimum for good growth and survival, maintaining high tissue levels of Mg, prevention of muscle flaccidity and skeletal deformity, and increasing the number of a whit blood cell (macrophage) migration in the presence of a substance produced by the bacteria E. ictaluri. However, supplemental levels of dietary Mg did not protect juvenile channel catfish from E. ictaluri infection. Since nutrient deficiency predisposes the animals to infectious diseases, it is recommended that an adequate level of Mg(400mg/kg) to meet fish requirements for growth and prevention of deficiency signs be included.
Technical Abstract: Juvenile channel catfish with an average weight of 10.89g and 4.14g were fed purified diets supplemented with magnesium(Mg) from Mg sulfate at levels of 0, 200, 400, 600, 800 and 1,000mg/kg and 0, 200, 400, 600 and 800mg/kg in studies I and II, respectively to evaluate the effect of dietary levels of Mg on growth performance, tissue mineral content, hematology, immune response and resistance to Edwardsiella ictaluri challence. Each diet was fed to fish in quadruplicate and triplicate aquaria to apparent satiation for 10 weeks for studies I and II, respectively. In both studies, weight gain, survival, dry matter feed intake and feed efficiency were lowest for fish fed the basal diet but increased with increasing dietary levels of Mg up to approximately 200mg/kg 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 200mg Mg diets. Bone Ca content did not differ among fish fed different diets (study I), but calcification of soft tissues. Macrophage chemotaxis in the presence of exoantigen was highest for fish fed diets supplemented with 400 and 200mg Mg/kg 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 400mg/kg. Thus, a dietary level of Mg of 400mg/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, however, had no effect on the resistance of juvenile channel catfish to E. ictaluri.