The impacts of seasonal variation on the immune status of Nile tilapia larvae and their response to different immunostimulants feed additives.

Few data are available on the thermal tolerance of Nile tilapia fish larvae in relation to their immune status and survival. The aims of this work were to evaluate the immune status of one day old Nile tilapia (Oreochromis niloticus) larval stage collected at the beginning (March), middle (August) and at the end (October) of hatching season through morphometric assessment of the larvae parameters including yolk sac diameter, body length and width as well as the expression of some immune-related genes (rag, sacs and tlr), inflammatory (il1b and il8) and stress related genes (hsp27, hsp70). Also, to compare the effect of three different immunostimulants (ß-glucan, Vitamin C, and methionine/lysine amino acids mix) on the expression of the studied genes at two variant temperatures (23 ± 1 °C and 30 ± 1 °C) in experimental study for 21 days. The immune status of Nile tilapia is affected by thermal fluctuation throughout the hatching season reflected by altered yolk sac size, length, and expression of the immune and stress related genes of the larvae, the best performances was observed at the beginning of the hatching season (March). High temperature (30 °C) suppress immune and stress responses throughout downregulation of all the genes under study, mask any effects for the immunostimulants, increased mortality in fish larvae suggesting narrow thermal tolerance range for the larvae compared with the adult fish. We recommend the use of amino acid mix as immunostimulant for Nile tilapia larvae, it reduces the mortality percentage and improve cellular response. Also, the use of ß-glucan should be prohibited during this developmental stage of larvae, it induced the highest mortality percentage.

Lead poisoning in Nile tilapia (Oreochromis niloticus): oxidant and antioxidant relationship.

Selenium and vitamin E are very effective antioxidant agents which play important roles in improving and development of aquaculture sector. This study was conducted to determine the protective and treatment effects of vitamin E and selenium against lead toxicity. Administration of both vitamin E and selenium ameliorated the adverse effects of lead acetate toxicity through significant increase in hemoglobin, packed cell volume, RBC count, WBC count, and lymphocytes compared to lead acetate-exposed groups especially after the 10th week. Also, it is revealed that severe decrease of total protein, calcium, phosphorous, and magnesium in lead acetate intoxicated group. On contrary, significant increase of blood parameters upon addition of vitamin E and selenium combined with/without lead. On the other hand, insignificant decreases of sAST, sALT, urea, and creatinine in group fed on vitamin E and selenium, while increase in lead acetate intoxicated group. Lead acetate caused increasing of lipid peroxidation level (malondialdehyde) and decreasing of superoxide dismutase activity and reduced glutathione level. From these results, it is concluded that exposure to lead acetate is considered as hepatotoxic environmental pollutant. Exposure to lead acetate induced significant effects on antioxidant status. Antioxidants (vitamin E and selenium) showed important roles to protect body against lipid peroxidation, which considered as the first step of cell membrane damage, in addition to the improvement of the endogenous antioxidant enzyme activities.