title: Interacting effects of water temperature and dietary protein level on hematological parameters in Nile tilapia juveniles, Oreochromis niloticus (L.) and mortality under Streptococcus iniae infection.
abstract: Based on central composite rotatable experimental design and response surface method, the interacting effects of temperature (20 °C-34 °C) and dietary protein level (25%-50%) on hematological parameters including red blood cell (RBC), white blood cell (WBC) and hemoglobin (Hb) of juvenile Oreochromis niloticus were studied under laboratory conditions. The experiment lasted for 7 weeks. After the feeding trial, fish were challenged with Streptococcus iniae and mortality was recorded for within 8 days. Results showed that the linear and quadratic effects of temperature on RBC, WBC and Hb were highly significant (P < 0.01). When the dietary protein level was 25%-50%, the RBC, WBC and Hb were increased firstly and then decreased, but the linear and quadratic effects of protein level were insignificant (P > 0.05). The interacting effects of temperature and protein level on RBC and Hb were significant (P < 0.05). The regression equations of RBC, WBC and Hb toward the two factors of interest were established, with the coefficients of determination being 0.870, 0.836 and 0.881, respectively (P < 0.01). These equations could be used for prediction in practice. After the challenge, the mortalities for the combinations of 22.1 °C/28.7% and 20.0 °C/37.5% were significantly higher than 27.0 °C/37.5% (P < 0.05). The optimal temperature/dietary protein level combination was obtained at 27.9 °C/38.1% at which the lowest mortality (13.76%) was attained. This value was close to the optimal temperature/dietary protein level combination (29.4 °C/41.9%) for the greatest levels of RBC (2.560 × 10(6) μL(-1)), WBC (270.648 × 10(3) μL(-1)) and Hb (92.851 g L(-1)). The results of this study indicated that preferred temperature/dietary protein level combination might strengthen the non-specific immunity and reduce susceptibility to S. iniae.
authors.affiliation: China Key Laboratory of Freshwater Fisheries and Germplasm Resources Utilization, Ministry of Agriculture, Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, Wuxi 214081, Jiangsu, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Qiang
authors.forename: Hong
authors.initials: H
authors.lastname: Yang
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.forename: Mathew D
authors.initials: MD
authors.lastname: Kpundeh
authors.forename: Pao
authors.initials: P
authors.lastname: Xu
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D023681:Cichlids / Q000276:immunology*; D004044:Dietary Proteins / Q000008:administration & dosage; D004198:Disease Susceptibility / Q000662:veterinary; D004906:Erythrocyte Count / Q000662:veterinary; D005393:Fish Diseases / Q000276:immunology* / Q000382:microbiology; D006452:Hemoglobinometry / Q000662:veterinary; D007113:Immunity, Innate; D007958:Leukocyte Count / Q000662:veterinary; D016014:Linear Models; D008954:Models, Biological; D013290:Streptococcal Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*; D013291:Streptococcus / Q000276:immunology*; D013696:Temperature; D014867:Water
chemical_list: D004044:Dietary Proteins; D014867:Water