Some studies on the immune status of cultured Oreochromis niloticus

Abstract

Lysine and methionine deficiency in cultured fish considred as one of the most notable nutritional constraints on the expansion of aquaculture and the realization of its full potential.

Lysine and methionine deficiency causes a poor growth rate implies that the immune responsiveness would be markedly impaired. Few studies, however, have been concerned with the effect of nutrients on the immune response. A dietary deficiency leads to immune suppression in fish . Inducing a protective immune response to a pathogenic organism before the individual fish becomes naturally exposed to it (Prophylaxis) seems at first sight an eminently sensible way of preventing an infectious. Improving feed efficiency, metabolic assimilation, immunity and minimizing mortality in fish farms through improvement of fish immunity against different fish diseases, is of high priority in contemporary animal production and it will cause reduction in production costs and improvement of fish production with minimizing feed costs.

Therefore, the present work was designed to investigate :

The effects of methionine and lysine amino acids deficiency on freshwater fish production and immunity through study :

a. The effect of methionine and lysine deficiency on: body weight, body weight gain, feed conversion and efficiency.

b. The effect of methionine and lysine on the immunity through study the effect of the deficiency of them on differential leucocytic counts, phagocytic activity and index .

c. The effect of methionine and lysine deficiency on tissues through histopathological studies and clinical studies as serum enzymes as sALT, sAST and Total proteins as well as serum bactericidal and lysozomal activity.

The effect of methionine and lysine deficiency on protection against infection by A. hydrophila by calculating relative level of protection and antibody titers after vaccination by bacterin of the same strain of A. hydrophila.

This study was carried-out on a total number of 120 healthy fish Oreocltromis niloticus, were obtained from private fish farm. The fish were in good healthy condition without any clinical manifestation. Fish were transported a live to the laboratory Departement of Poultry and Fish Disease of Faculty of Veterinary Medicine, Alexandria Univeristy in plastic bags containing water enriched by air (2/3).Average body weight of fish about 50± 5 g.

The results of this study concluded that :

I. Deficiency of methionine and lysine causes decreasing of body weight, body weight gain and fed conversion than the control group.

2. The most important clinical signs of fish due to methionine and lysine deficiency include severe emaciation, lethargy, decreasing immunity against different diseases. In addition to, appearance of nervous signs, haemorrhages on the body surfaces with exophthalmia.

3. The post-mortem examination revealed the presence of enlargement of different body • organs in addition to presence of the bloody fluid in the abdomen.

4. The most important Histopathologic results indicated that, the nature of the encountered lesions due lysine and methionine deficiency depend up on concentration of the methionine and lysine and if the deficiency lysine only or methionine only or both with each other.

5. The results of haematological studies indicated that, the lymphocytes, monocytes, basophils and eosinophils percentages decreased severly in deficiency of methionine and lysine followed by methionine only but the deficiency of lysine not affected severly on lymphocyte , but its effect on monocyte and basophils is severly than the methionine deficiency.