Figure 1
Effect of oxytetracycline and florfenicol on O. niloticus growth performance (A) Bars indicate initial body weight, final body,weight gain (g) and (B) Bars indicate food conversion ratio (FCR). Data presented as mean ± SD. Different letters stand for statistically significant differences at P < 0.05
Figure 2
Effect of oxytetracycline and florofenicol on O. niloticus immunological status (A) Serum IgM and phagocytic activity, (B)serum lysozyme activity. Data presented as mean ± SD. Different letters stand for statistically significant differences at P <0.05.
antibiotics limit microbial population numbers and their production of toxins and by-products which reduce the competition with the host for vital nutrients, and they enhance the
absorption and utilization of nutrients due to a thinning of the intestinal wall. Gaskins et al. (2002) demonstrated that the effect of oxytetracycline in growth promotion depends on the reduction of the gastrointestinal tract bacteria. Dibner and Richards (2005) demonstrated that the reduction in microflora,and its consequences, may be the underlying mechanism for the beneficial effect of antibiotics.
Herein the immunological study showed insignificant differences between G3 and a control group in the immunoglobulin M (IgM) total level while there was a significant decrease in G2. The phagocytic activity of G3 had an insignificant decrease than the control group. Lysozyme activities of all treated groups significantly increased compared to the control group. Other works emphasized the same results and found that OTC suppresses the antibody production, the level of circulating leukocytes as well as phagocytic activity in rainbow trout, sea bream and Koi carp (Lunden et al., 1998; Serezli et al., 2005; Kasagala and Pathiratne, 2008). Salmonid specific and nonspecific immune responses were depressed by administration of tetracycline at 10 mg kg1 diet (Siwicki et al., 1989).Sea bream were fed diets supplemented with OTC at 4 and
8 mg g1 feed for 21 days inducing a decrease in the humoral innate immune parameters and an increase in the cellular parameters (Guardiola et al., 2012). In contrary of our findings,
the oral administration of OTC in turbot (Scophthalmus maximus L.) had no effect on the respiratory burst and phagocytosis activities (Taffalla et al., 1999). Sea bream’s total erythrocyte,leukocyte and nitroblue tetrazolium (+) cells were increased by administration of OTC at 75 mg kg1 body weight for 10 days and lasted around 21 days after ceasing the administration, then returned to normal levels (Serezli et al., 2005). On the other hand, FLO did not significantly influence the immune parameters of rainbow trout at 20 mg kg1 BW day1 despite a slight effect on the phagocyte function being indicated (Lunden et al., 1999). Similarly,hybrid tilapia fed on FLO supplemented diet at 0.02 g kg1 BW for 16 weeks were unaffected by serum lysozyme activity,head kidney macrophage phagocytic index (He et al.,2011).
The conflicting results may be due to different conditions used in various studies beside fish species, temperature, antibiotic dose and route of administration which affect drug absorption (Bjo¨ rklund and Bylund, 1990). Lunden et al.(2002) found that OTC and FLO are retained in pronephros which is an important lymphoid organ of fish; accordingly,the OTC and FLO could interact with the immune cells and have an influence on immune responses. OTC suppression of
immune response may be attributed to the penetration of OTC to immune cells and impair their function (Hand et al.,1990). Reduction in the phagocytic index may be attributed to OTC induced suppression of total neutrophils in the blood stream which is responsible for enhancement of the phagocytic activity of monocytes (Evelyn, 2002). Unlike OTC, FLO therapy did not suppress circulating leukocyte levels or antibody production in rainbow trout (Lunden et al., 1998). Reports concerning FLO are even more controversial, but there is a consensus that its effects appear to be less pronounced than those demonstrated for OTC (Romero et al., 2012).
The biochemical results corroborated the demonstration to the histopathological finding of both liver and kidney. The significant changes in the activities of aspartate transaminase
(AST) and alanine aminotransferase (ALT) enzymes in blood indicated tissue impairment caused by stress, toxicity and liver damage produced by drugs and antibiotics (Kori-Siakpere et al.,2010). Alternatively, this disrupted the cell membranes,allowing the enzymes to leak out of the cells. Oxytetraycline greatly impair the liver regeneration and decrease the mitochondrial protein synthesis after causing deficiency in cytochrome oxidase C and ATP synthetase enzymes (Den Bogert et al., 1983). Serum creatinine and uric acid can be used as a rough index of the glomerular filtration rate (GFR) (Hernandez and Coulson, 1967). The results of urea and creatinine may be due to pathological alterations of the treated fish kidney.
The previous studies on the effect of OTC and FLO on the histopathological findings in fish species are conflicting. In Tinca tinca on the 7th day of OTC intramuscular injection it
showed severe necrosis of hematopoietic renal tissue with fatty degeneration in the liver (Soler et al., 1996). Also, the OTC medicated feed which was administered at 15 g kg1 live weight
diffuses cytoplasmic vacuolization of the renal duct epithelium in kidney of C. carpio (Svobodova et al., 2006). FLO administration in the feed of tilapia spp. at 15, 45, or 75 mg/kg body weight for 20 days led to increased glycogen-type and lipid-type with hepatocellular vacuolation in the liver, decreased lymphocytes,increased blast cells, and increased individual cell necrosis in the anterior kidney, and tubular epithelial degeneration and mineralization in the posterior kidney (Gaikowski et al.,2012). Similarly, FLO administration in channel catfish at doses of 10, 30, or 50 mg/kg BW/d for 20 days, showed a dose-dependent decrease in hematopoietic/lymphatic tissue in the anterior kidney, posterior kidney, and spleen (Gaikowski
et al., 2003). Conversely, FLO administration in feed to Atlantic salmon parr at 100 mg/kg BW/d for 10 days or at 50 mg/kg BW/d for 10 days on/off cycles did not induce treatment-related
histopathologic lesions in the liver, or kidney (Inglis et al.,1991). Also, FLO administration in feed at up to 75 mg/kg BW/d for 20 days to Sunshine bass did not show any hepatic or nephric tissue alteration (Straus et al., 2012).
Oxytetracycline and Florfenicol residues in muscles of fish samples showed 0.05 and 0.04 lg g1 muscle, respectively after fifteen days of feeding cessation. The obtained results were lower than the maximum residue limits (MRLs) of Oxytetracycline and Florfenicol (0.1 and 1 lg g1, respectively) according to Commission regulation, EU (2010).
Figure 3
Effect of oxytetracycline and florofenicol on ALT and AST activity of O. niloticus. Data presented as mean ±SD.Different letters stand for statistically significant differences at
P <0.05.
Figure 4
Effect of oxytetracycline and florofenicol on (A) urea and (B) creatinine value of O. niloticus. Data presented as mean ± SD Different letters stand for statistically significant differences at P < 0.05.
Figure 5
Histopathological sections of liver of O. niloticus (A) fed on basal diet (B) fed on OTC at 100 mg kg1 diet showed congestion (arrow head), severe fatty change and vacuolations in the epatocytes (arrow) and (C) fed on FLO at 5 mg kg1 body weight showed diffused hydropic degeneration in the hepatocytes (arrow) and activation of melanomacrophage center (arrow head) (HE, Bar =100 lm).
Figure 6
Histopathological sections of kidney of O. niloticus (A) fed on basal diet (B) fed on OTC at 100 mg kg1 diet showed periglomerular lymphocytic aggregation (arrow) and (C) fed on FLO at 5 mg kg1 body weight showed shrunken glomerular tufts and dilation of Bowman’s capsule (arrows). (HE, Bar= 100 lm).
Conclusion
From the previous study, it can be concluded that addition of FLO at 5 mg kg1 body weight is more safe with its effect on growth performance, immunity, liver and kidney functions of
O. niloticus and for human food safety. Besides great care on the excessive use of antibiotics in the aquatic environment to avoid the terrible effects of them it resulted in the emergence
of antibiotic-resistant bacteria in aquaculture as well as the transfer of these resistance determinants of human pathogens and antibiotic residues in fish tissue and fish products.
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