Long-term feeding of Atlantic salmon with varying levels of dietary EPA + DHA alters the mineral status but does not affect the stress responses after mechanical delousing stress.

Atlantic salmon were fed diets containing graded levels of EPA + DHA (1·0, 1·3, 1·6 and 3·5 % in the diet) and one diet with 1·3 % of EPA + DHA with reduced total fat content. Fish were reared in sea cages from about 275 g until harvest size (about 5 kg) and were subjected to delousing procedure (about 2·5 kg), with sampling pre-, 1 h and 24 h post-stress. Delousing stress affected plasma cortisol and hepatic mRNA expression of genes involved in oxidative stress and immune response, but with no dietary effects. Increasing EPA + DHA levels in the diet increased the trace mineral levels in plasma and liver during mechanical delousing stress period and whole body at harvest size. The liver Se, Zn, Fe, Cu, and Mn and plasma Se levels were increased in fish fed a diet high in EPA + DHA (3·5 %) upon delousing stress. Furthermore, increased dietary EPA + DHA caused a significant increase in mRNA expression of hepcidin antimicrobial peptide (HAMP), which is concurrent with downregulated transferrin receptor (TFR) expression levels. High dietary EPA + DHA also significantly increased the whole-body Zn, Se, and Mn levels at harvest size fish. Additionally, the plasma and whole-body Zn status increased, respectively, during stress and at harvest size in fish fed reduced-fat diet with less EPA + DHA. As the dietary upper limits of Zn and Se are legally added to the feeds and play important roles in maintaining fish health, knowledge on how the dietary fatty acid composition and lipid level affect body stores of these minerals is crucial for the aquaculture industry.

Synthetic pyrethroid effect on blood plasma biomarker enzymes and histological changes in Catla catla.

Alpha-cypermethrin is an isoform of cypermethrin; it is an active pyrethroid used extensively to control a wide range of pests in agriculture and animal breeding. In this study four groups of six fish were examined. The first group served as a control in fresh water alone, with no pyrethroid. The second, third and fourth groups were exposed to alpha-cypermethrin for 4, 8 and 96 h respectively. At the end of the each exposure period, the fish were sacrificed, and the required muscle tissues were collected for histological examination. The blood was drawn with heparinized needles and processed for serum enzymatic studies. Serum enzymes such as aspartate transaminase (AST), alanine transaminase (ALT), amylase, acid phosphatase (ACP) and gamma-glutamyl transpeptidase (GGT) were measured at 4, 8 and 96 h. AST enzyme activity was significantly increased at 4 h, whereas ALT and amylase enzyme activities were significantly reduced at all the time points. ACP enzyme activity was significantly reduced at 4 and 8 h, whereas GGT enzyme activity was significantly increased at all the time points. Hepatocyte cytoplasmic vacuolisation and degeneration, rupture of blood vessels, and necrosis was found at all time points. Congestion of blood vessels, bulging, distortion of filaments, erosion and disintegration of blood corpuscles and hyperplasia of epithelium were found in treated gills at 4, 8 and 96 h. Breakdown of muscle fibres, vacuolation and accumulation of lipids and melanin in white muscle were observed in treated fish muscle at 4, 8 and 96 h.

Impact of dietary level and ratio of n-6 and n-3 fatty acids on disease progression and mRNA expression of immune and inflammatory markers in Atlantic salmon (Salmo salar) challenged with Paramoeba perurans.

The aim of the study was to investigate the influence of dietary level and ratio of n-6/n-3 fatty acids (FA) on growth, disease progression and expression of immune and inflammatory markers in Atlantic salmon (Salmo salar) following challenge with Paramoeba perurans. Fish (80 g) were fed four different diets with different ratios of n-6/n-3 FA; at 1.3, 2.4 and 6.0 and one diet with ratio of 1.3 combined with a higher level of n-3 FA and n-6 FA. The diet with the n-6/n-3 FA ratio of 6.0 was included to ensure potential n-6 FA effects were revealed, while the three other diets were more commercially relevant n-6/n-3 FA ratios and levels. After a pre-feeding period of 3 months, fish from each diet regime were challenged with a standardized laboratory challenge using a clonal culture of P. perurans at the concentration of 1,000 cells L-1. The subsequent development of the disease was monitored (by gross gill score), and sampling conducted before challenge and at weekly sampling points for 5 weeks post-challenge. Challenge with P. perurans did not have a significant impact on the growth of the fish during the challenge period, but fish given the feed with the highest n-6/n-3 FA ratio had reduced growth compared to the other groups. Total gill score for all surfaces showed a significant increase with time, reaching a maximum at 21 days post-challenge and declined thereafter, irrespective of diet groups. Challenge with P. perurans influenced the mRNA expression of examined genes involved in immune and inflammatory response (TNF-α, iNOS, IL4-13b, GATA-3, IL-1ß, p53, COX2 and PGE2-EP4), but diet did not influence the gene expression. In conclusion, an increase in dietary n-6/n-3 FA ratio influenced the growth of Atlantic salmon challenged with P. perurans; however, it did not alter the mRNA expression of immune genes or progression of the disease.