Response of the salmon somatotropic axis to growth hormone administration under two different salinities

We compared the response of plasma insulin-like growth factor-I (IGF-I) to growth hormone (GH) administration under two different salinities to test the hypothesis that environmental salinity alters the "activity" of the GH-IGF-I axis. In July, postsmolt coho salmon reared in fresh water (FW) were transferred to either FW or half seawater (1/2 SW) (15 ppt) tank. During the experiment, water temperature was maintained at 10℃ for both salinities; photoperiod was adjusted to that of Seattle (48°N), and fish were not fed. Two days after transfer, fish were injected once with porcine GH (pGH) at a dose of 2 or 8 μg/g body weight. Liver and blood samples were collected 1, 2 and 3 days after injection. Liver GH receptor (GHR) mRNA expression was analyzed by quantitative real-time RT-PCR, and plasma IGF-I, 41-kDa IGF-binding protein (main carrier of IGF-I) and pGH were quantified by radioimmunoassays. Transfer to 1/2 SW resulted in transient increases in basal levels of liver GHR mRNA and 41 kDa IGF-binding protein (IGFBP) but not IGF-I. The GH-injection increased liver GHR mRNA, plasma IGF-I and 41-kDa IGFBP in fish in both FW and 1/2 SW. However, the time course and magnitude of the response differed between salinities. Fish in FW receiving 8 μg/g pGH had the highest IGF-I levels (63.7 ± 6.8 ng/ml) one day after injection, whereas fish in 1/2 SW showed a peak (88.8 ± 14.3 ng/ml) two days after injection of the same dose. It is speculated that the prolonged response to GH by fish in 1/2 SW may be due to slower disappearance of pGH from the circulation in fish in 1/2 SW. The transient increase in basal liver GHR mRNA may also contribute to a greater response for fish in 1/2 SW. These results suggest that salinity is capable of altering the "activity" of the GH-IGF-I axis in salmon

Evaluation of the in vivo and in vitro interleukin-12 p40 and p35 subunit response in yellowtail (Seriola quinqueradiata) to heat-killed Lactobacillus plantarum strain L-137 (HK L-137) supplementation, and immersion challenge with Lactococcus garvieae

Dietary supplementation of immunostimulants might be effective to reduce the economic losses due to infectious diseases and the use of antibiotics in aquaculture. To investigate the immune response of interleukin-12 (IL-12) in yellowtail Seriola quinqueradiata to heat-killed Lactobacillus plantarum strain L-137 (HK L-137), we performed a leukocyte culture, feeding trial with diets containing L-137 and an immersion challenge with Lactococcus garvieae. IL-12 (IL-12p70) is a heterodimeric cytokine composed of IL-12p35 and IL-12p40 subunits. In the yellowtail-leukocyte culture, HK L-137 treatment stimulated the mRNA expression of one IL12p35 subunit (p35a) and all IL12p40 subunits (p40a, p40b, and p40c) in a dose-dependent manner. Furthermore, mRNA expression of type-I helper (Th-1) cytokine (tumor necrosis factor α, TNF-α, and interferon γ, IFN-γ) was also stimulated by HK L-137. After 6 weeks of feeding yellowtails with diets containing 0, 20, and 100 ppm of HK L-137, the mRNA expression of p35a and p40b in the spleen leukocytes increased with the dietary concentration of HK L-137, and that of p40b, p40c, and ifng in the head kidney leukocytes were the highest in the 20 ppm HK L-137 group. Survival rates in the 20 ppm HK L-137 group after immersion challenge with L. garvieae were significantly higher than the control (0 ppm of HK L-137). The 100 ppm HK L-137 group did not significantly suppress mortality. HK L-137 showed immunostimulant activity by increasing the expression of il-12, tnfa, and ifng mRNA in both in vitro and in vivo tests in yellowtail. Our results suggest that dietary supplementation with 20 ppm HK L-137 is the most efficient dose for improving immunity in yellowtail. Furthermore, a high dose of HK L-137 and/or long-term feeding of a diet containing HK L-137 might suppress the immune response, which probably decreases the survival rate of fish. To maintain a high immune response in yellowtail, the optimal dietary concentration of HK L-137 and/or feeding regime should be investigated further

Effect of a plant-based low-fishmeal diet on digestive physiology in yellowtail Seriola quinqueradiata

To characterize the effects of a plant-based low-fishmeal (LFM) diet on the digestive physiology of yellowtail, Seriola quinqueradiata, we prepared two isonitrogenous and isolipidic diets; an FM-based diet (diet Control, FM 50%) and a plant protein (soybean meal and corn gluten meal)-based low fishmeal diet (diet LFM, FM 15%), and examined the acute and chronic effects of the diets on the digestive physiology of the fish were examined. In the acute effect trial (fed only a single meal), the fish fed the LFM diet displayed faster gastric emptying, lower pH of the gastrointestinal content and suppressed pancreatic digestive enzymes (trypsin, chymotrypsin and amylase) secretions. In the chronic effect trial (feeding for six weeks), in addition to the effects observed in the acute trial, the fish fed the LFM diet also displayed suppressed stomach pepsin secretion and pancreatic digestive enzymes production (gene expression). Furthermore, gene expression levels of digestion-regulating hormones, gastrin, cholecystokinin and peptide yy were also disrupted by the long-term administration of the LFM diet. Taken together, these results indicate that a plant protein-based low fish meal diet appears to not fully activate or stimulate the digestive system of yellowtail in either the short or long term and that its inhibitory/disruptive effects become more pronounced on a long-term basis. The effects we have identified on yellowtail digestive physiology could serve as important indicators to improve the plant-based low-fishmeal diets

Effect of a plant-based low-fishmeal diet on digestive physiology in yellowtail Seriola quinqueradiata

To characterize the effects of a plant-based low-fishmeal (LFM) diet on the digestive physiology of yellowtail, Seriola quinqueradiata, we prepared two isonitrogenous and isolipidic diets; an FM-based diet (diet Control, FM 50%) and a plant protein (soybean meal and corn gluten meal)-based low fishmeal diet (diet LFM, FM 15%), and examined the acute and chronic effects of the diets on the digestive physiology of the fish were examined. In the acute effect trial (fed only a single meal), the fish fed the LFM diet displayed faster gastric emptying, lower pH of the gastrointestinal content and suppressed pancreatic digestive enzymes (trypsin, chymotrypsin and amylase) secretions. In the chronic effect trial (feeding for six weeks), in addition to the effects observed in the acute trial, the fish fed the LFM diet also displayed suppressed stomach pepsin secretion and pancreatic digestive enzymes production (gene expression). Furthermore, gene expression levels of digestion-regulating hormones, gastrin, cholecystokinin and peptide yy were also disrupted by the long-term administration of the LFM diet. Taken together, these results indicate that a plant protein-based low fish meal diet appears to not fully activate or stimulate the digestive system of yellowtail in either the short or long term and that its inhibitory/disruptive effects become more pronounced on a long-term basis. The effects we have identified on yellowtail digestive physiology could serve as important indicators to improve the plant-based low-fishmeal diets