For rainbow trout Oncorhynchus mykiss, high temperature is a major abiotic stress that limits its growth and productivity. In this study, spleen macrophage respiratory burst (RB), serum superoxide dismutase (SOD), serum malondialdehyde (MDA) and mRNA expression of the SERPINH1 (HSP47) gene in different tissues (liver, spleen, head kidney and heart) were measured in unstressed (18 °C) and heat-stressed (25 °C) fish. Spleen macrophage RB activity, serum SOD activity and MDA content all increased significantly (P < 0.05) during heat shock, and peaked at 8, 12 and 4 h, respectively. SERPINH1 mRNA expression responded in a time- and tissue-specific manner to heat stress, which was mainly reflected in the significant up-regulation in all tissues (P < 0.05) and greater expression in the liver than the other tissues (P < 0.05). During the heat-shock recovery period, the MDA content returned to the unstressed level. These results indicate that heat shock causes cell injury, induces oxidative damage and promotes SERPINH1 mRNA expression, which plays an important protective function during heat stress in O. mykiss. In practice, close attention should be given to temperature changes in O. mykiss production to reduce the effects of high temperature.

ABSTRACT. The enhanced expression of heat shock proteins (hsps) in organisms can be detected in response to many kinds of stressor. For fish, high temperature is an important stressor, and hsp expression is associated with differences in environmental temperature. In this study, rainbow trout (Oncorhynchus mykiss) that were accustomed to an aquatic temperature of 18°C were exposed to an elevated temperature (25°C), and hsp60 expression in the gill, liver, spleen, heart, and head kidney was quantified using real-time polymerase chain reaction in unstressed and heat-stressed animals. The fish responded to heat stress in a time-and tissue-specific manner. Cardiac hsp60 mRNA levels were largely unchanged, and the greatest induction of hsp60 in heat-stressed animals was recorded in the liver, suggesting that protein damage and the consequent requirement for the Hsp60 protein are probably greater in hepatic tissue. Therefore, fish must be provided with optimal 5281 Hsp60 expression response to heat stress in trout ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 14 (2): 5280-5286 (2015) temperature conditions in order to realize their potential growth and maximize fish farm profits.

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Infectious haematopoietic necrosis virus (IHNV) is a serious pathogenic threat to rainbow trout (Oncorhynchus mykiss) and other salmonids. Major histocompatibility complex (MHC) polymorphisms have been closely linked to disease susceptibility. In this study, polymerase chain reaction-singlestrand conformation polymorphism, cloning and sequencing were used to examine MHC class II b chain gene (DAB) polymorphisms and analyse their association with IHNV in rainbow trout. The DAB exon 2 was amplified from 104 resistant and 91 susceptible fish. Forty-five different alleles were identified, 30 of which were novel. Individuals possessed between one and four alleles, indicating that the genome harbours at least two closely related DAB exon 2 loci. The percentages of amino acid mutations in the peptide binding region (PBR) and non-PBR were 66.67% and 45.28% respectively. The rate of non-synonymous substitutions occurred at a significantly higher frequency than synonymous substitutions, suggesting the existence of balancing selection for maintenance of polymorphisms at the DAB exon 2 locus. The alleles Onmy-DAB*0201 (P < 0.001), Onmy-DAB*0904 (P < 0.001) and Onmy-DAB*1102 (P < 0.01) were associated with susceptibility to IHNV, while Onmy-DAB*0103, Onmy-DAB*0601 and Onmy-DAB*1402 were associated with resistance (P < 0.001). These alleles could be used as molecular markers for IHNV resistance breeding in rainbow trout.