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Several studies describe gastrointestinal tract (GIT) melatonin (MEL) synthesis from 5-HT, which itself derives from the essential amino acid l-tryptophan (l-trp) in the intestine. Supplementing l-trp and MEL through diet has shown social-response effects and suppresses neuroendocrine stress in teleosts. In this study, the effects of a MEL and l-trp-supplemented diet on the endocrine intestinal function and enzymatic response activity of two salmonid species were examined. To assess the possible effect of l-trp and MEL on intestinal serotonin content and digestive enzyme activity, three l-trp-supplemented diets and three MEL-supplemented diets were orally administered to a group of Salmo salar and Oncorhynchus kisutch for seven days under normal density conditions. Plasma biochemistry (cortisol, l-trp, MEL) as well as enzyme activity (amylase, lipase, and total protease) and serotonin content were measured in the pyloric caeca, midgut, and hindgut. Plasma l-trp levels were found to be directly related to l-trp supplemented diet levels. Similarly, MEL supplementation increased plasma MEL levels, and the presence of MEL in both salmon species resulted in a significant interaction with cortisol concentrations in plasma, and the highest concentrations of l-trp caused an increased GIT content for 5-HT in S. salar. No differences were seen in the GIT content for 5-HT for the l-trp supplemented diets in O. kisutch. An inhibitory effect was found on digestive enzymes in the supplemented diets of both salmonid species. In general, the presence of MEL in the diet reduced cortisol levels; diets supplemented with l-trp and MEL had either a stimulatory or inhibitory effect on digestive enzyme activity, which seemed to be indirect and tissue dependent.

Although Caligus rogercresseyi negatively impacts Chilean salmon farming, the metabolic effects of infection by this sea louse have never been completely characterized. Therefore, this study analyzed lactate responses in the plasma, as well as the liver/muscle lactate dehydrogenase (LDH) activity and gene expression, in Salmo salar and Oncorhynchus kisutch infested by C. rogercresseyi. The lactate responses of Atlantic and Coho salmon were modified by the ectoparasite. Both salmon species showed increasing in plasma levels, whereas enzymatic activity increased in the muscle but decreased in the liver. Gene expression was overexpressed in both Coho salmon tissues but only in the liver for Atlantic salmon. These results suggest that salmonids need more energy to adapt to infection, resulting in increased gene expression, plasma levels, and enzyme activity in the muscles. The responses differed between both salmon species and over the course of infection, suggesting potential species-specific responses to sea-lice infection.

Salt baths in the production system of salmonids in fresh water, are important for the prevention and control of different diseases such as saprolegnia fungus. This standard procedure generates a rapid depletion of O2 in the water, leading to a significant increase of CO2, affecting blood parameters associated with animal welfare, such as Na+, Cl-, glucose and protracted hypercarbia. The aim of this study was to evaluate the response field of blood parameters related to fish welfare and the physical-chemical parameters of water to which they are subject during this period, comparing two sets of bath salt. One group of farmed Atlantic salmon(Salmo salar)in the pre-smolt stage was exposed in a salt bath system with the usual conditions and a second to a recirculation system with a waterfall for degasification, with two different exposure periods of one and two hours. The results of the concentration of CO2in the water show significant variations between the two systems without recirculation compared to the control condition and salt. Significant differences were observed between the recirculating system and the control in blood levels of pCO2 and HCO3, but not pH. Our field data also show that salt baths that are performed regularly at the fish farms generate significant effects on blood parameters associated with animal welfare specifically fish pCO2and HCO3causing minor hypercarbia without generating blood acidosis. The addition of water recirculation with a waterfall does not affect blood parameters., Los baños de sal, dentro del sistema productivo de salmónidos en agua dulce, son un paso clave en la prevención y el control de diferentes enfermedades como la saprolegnia. Este procedimiento habitual genera un agotamiento rápido del O2en el agua, lo que genera un aumento significativo del CO2en el agua, afectando parámetros sanguíneos asociados a bienestar animal, como Na+, Cl-, glucosa y en situaciones prolongadas hipercapnia. Este trabajo tiene como objetivo evaluar en terreno la respuesta de parámetros sanguíneos asociados a bienestar de los peces y parámetros físico-químicos del agua a la que están sometidos en este periodo, comparando dos sistemas de baño de sal. Para ello se sometió a un grupo deSalmo salaren etapapre-smolta un baño de sal habitual, otro grupo a un sistema de recirculación con cascada de agua para su desgasificación y un grupo control sin sal, exponiéndolos a diferentes periodos de una y dos horas. Los resultados de la concentración de CO2en el agua muestran variaciones significativas entre ambos sistemas con y sin recirculación para la condición control y con sal. Los niveles sanguíneos evaluados en terreno de PCO2y HCO3presentaron diferencias significativas respecto del sistema con recirculación y al control, no así los niveles sanguíneos de pH. Nuestros datos de terreno demuestran que los baños de sal que se realizan con regularidad en los centros de cultivo generan efectos significativos sobre parámetros sanguíneos asociados a bienestar animal de los peces, específicamente PCO2 y HCO3, provocando hipercapnia leve sin generar acidosis sanguínea, al añadir recirculación del agua con una cascada a los baños de sal, no se ven afectados los parámetros sanguíneos.

Caligus rogercresseyi sea lice negatively impact Chilean salmonid farming, but no complete characterization for the metabolic effects of Caligus infestation currently exists. Therefore, the aim of this study was to analyze the effects of C. rogercresseyi infestation on the metabolic responses of Salmo salar and Oncorhynchus kisutch. Energy metabolism responses to C. rogercresseyi were examined over a time-course infestation of both salmonid species. Plasma metabolite levels and enzymatic activities related to intermediate metabolisms of carbohydrate, amino acid, and lipid were evaluated in the liver and muscle. Plasma glucose levels changed in both salmonid species, increasing at 1–3 days post-infestation. In turn, triglyceride levels increased at days 3 and 7 in O. kisutch and S. salar, respectively, while protein and total α-amino acids increased in O. kisutch but decreased in S. salar during infestation. Amino acid intermediate catabolic metabolism in the liver and muscle of O. kisutch increased during infestation, indicating a higher use of the gluconeogenic pathway than S. salar. Lipid intermediate anabolic metabolism increased in O. kisutch liver, remained unchanged in S. salar liver, and increased 1 day post-infestation in the muscle of both salmonids. Liver and muscle carbohydrate intermediate anabolic metabolism in O. kisutch increased during infestation, suggesting that this species preferentially uses the glycogenolytic-glucolytic pathway, in contrast with S. salar. In conclusion, amino acid and carbohydrate catabolism enzymes in O. kisutch activated soon after initial sea lice infestation, which would allow this species to dispose of energy substrates earlier than S. salar. This physiological data contributes towards the ability of O. kisutch to more adeptly cope with the increased energy demand imposed by C. rogercresseyi infestation.