Stocking density and Piscirickettsia salmonis infection effect on Patagonian blennie (Eleginops maclovinus, Cuvier 1830) skeletal muscle intermediate metabolism

Abstract

The need to expand aquaculture production has led to other fish to be considered as potential species for culture, such as the sub-Antarctic notothenioid Eleginops maclovinus (Valenciennes, 1830). The aim of this study was to determine the cumulative effect of density and pathogen infection by protein extract of Piscirickettsia salmonis on skeletal muscle metabolism. In a first experiment, specimens were submitted to three different stocking densities: (1) 3.1 kg m(-3), (2) 15 kg m(-3) and (3) 60 kg m(-3), for a period of 10 days. In a second experiment, metabolic changes caused by an infection of P. salmonis protein extract (a single injection of 0.5 μL P. salmonis protein extract g body weight(-1) was inoculated in the fish) and its combined effect with stocking density was assessed during a period of 10 days. This study concludes that stress caused by high stocking density led to the reorganization of some metabolic routes to fulfill skeletal muscle energy needs. Furthermore, infection response by pathogen P. salmonis differed when stocking density increased, suggesting an increase of energy needs with density in skeletal muscle of infected fish.

Intermediary metabolic response and gene transcription modulation on the Sub‐Antarctic notothenioid Eleginops maclovinus (Valenciennes, 1930) injected with two strains of Piscirickettsia salmonis

“…For instance, in E. maclovinus acclimated to different environmental salinities, G6PDH in the liver did not show variation, whereas in individuals of the same species exposed to high salinity conditions, activity of G6PDH decreased (Vargas‐Chacoff, Moneva, et al, ; Vargas‐Chacoff et al, ). Additionally, an increase in the hepatic activity of G6PDH has been observed in E. maclovinus exposed to stressful high stocking density conditions (Vargas‐Chacoff, Ortiz, et al, ). Their results, combined with our study, suggest that an increase of G6PDH after inoculation with AUSTRAL‐005 could be related to the need of glucose oxidation via pentose phosphate shunt, elevating the reducing power (NADPH) and lipid biosynthesis, which is needed as a source of energy due to a higher demand trigger by the antibiotic‐resistant strain.…”

“…Our results showed that after inoculation with both strains of P. salmonis , an increase in the cortisol levels was observed, being higher in fish injected with AUSTRAL‐005 (Figure a). This glucocorticoid is utilized as an indicator of stress in fish and can suppress the phagocytic and complement activity, increasing the susceptibility to develop the infection in the fish after P. salmonis inoculation (Pickering & Stewart, ; Vargas‐Chacoff, Martinez, et al, ; Vargas‐Chacoff, Ortiz, et al, ; Wendelaar‐Bonga, ). Previous studies have shown similar increases in E. maclovinus cortisol levels after being inoculated with total protein of wild‐type P. salmonis and then exposed to high stocking density (Vargas‐Chacoff, Martinez, et al, ).…”

“…Protein concentration was measured following the bicinchoninic acid method (Pierce #23225). Enzyme assays were carried out at initial velocity conditions, before stabilizing due to substrate consumption, and the specific conditions for enzyme assays were described elsewhere (Oyarzún, Muñóz, Pontigo, Morera, & Vargas-Chacoff, 2018;Sangiao-Alvarellos et al, 2005;Vargas-Chacoff, Arjona, et al, 2009;Vargas-Chacoff, Ortiz, et al, 2014).…”

“…After infection occurs, the stress produced by the bacterial infection makes the fish reallocate energy to maintain the homoeostasis, moving away from investment activities such as growth and reproduction, towards activities like locomotion, hydromineral regulation and tissue repair, reducing the performance capacity and the immunological response during chronic stress (Schreck, ; Vargas‐Chacoff, Moneva, et al, , ; Wendelaar‐Bonga, ). The stress associated with bacterial infections increases the cortisol levels, a glucocorticoid indicator of stress in fish, causing a decrease in lymphocyte numbers, suppression of phagocytes and complement activity, and the modulation of enzymes involved in the metabolism of carbohydrates, lipids and amino acids (Law, Chen, Song, Dufour, & Chang, ; Librán‐Pérez, Costa, Figueras, & Novoa, ; Oyarzún, Vargas‐Lagos, et al, ; Pickering & Stewart, ; Vargas‐Chacoff, Moneva, et al, ; Vargas‐Chacoff, Ortiz, et al, ; Wendelaar‐Bonga, ). Moreover, fish infected with pathogens like P. salmonis can experience variations in plasma glucose levels, total amino acids, lactate and triglycerides to satisfy a greater energy demand caused by chronic infections (Miwa & Mano, ; Peng, Ma, Zhang, & Li, ; Peters, Faisal, Lang, & Ahmed, ; Vargas‐Chacoff, Ortiz, et al, ).…”

“…The stress associated with bacterial infections increases the cortisol levels, a glucocorticoid indicator of stress in fish, causing a decrease in lymphocyte numbers, suppression of phagocytes and complement activity, and the modulation of enzymes involved in the metabolism of carbohydrates, lipids and amino acids (Law, Chen, Song, Dufour, & Chang, 2001;Librán-Pérez, Costa, Figueras, & Novoa, 2018;Oyarzún, Vargas-Lagos, et al, 2019;Pickering & Stewart, 1984;Vargas-Chacoff, Moneva, et al, 2014;Vargas-Chacoff, Ortiz, et al, 2014;Wendelaar-Bonga, 1997). Moreover, fish infected with pathogens like P. salmonis can experience variations in plasma glucose levels, total amino acids, lactate and triglycerides to satisfy a greater energy demand caused by chronic infections (Miwa & Mano, 2000;Peng, Ma, Zhang, & Li, 2015;Peters, Faisal, Lang, & Ahmed, 1988;Vargas-Chacoff, Ortiz, et al, 2014). The physiological changes associated with P. salmonis infection not only represents an important problem to salmon species utilized in the Chilean aquaculture, but also to other fish species living in close proximity to sea cages.…”