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In the present study, the histological changes and digestive enzymatic activity patterns are described during the larval development of palm ruff, Seriolella violacea from hatching up to 50 days after hatching (DAH). At hatching, the digestive tract consisted of an undifferentiated straight tube dorsal to the yolk-sac, which presented alkaline protease activity (trypsin and chymotrypsin) as well as amylase and lipase activities with similar patterns during larval development. At 20 and 23 DAH, histology of the stomach revealed a sac-like shaped organ, with an epithelium that began to differentiate in a cardiac and a pyloric region. Typical histological structures of a stomach were visible at 33 DAH with a concomitant pepsin activity. Gastric glands were clearly visible at 35 DAH, increasing in numbers up to 37 DAH, suggesting a functional stomach at this age. A significant increase in the specific activity of all enzymes including pepsin (except amylase) was observed between days 33–35 DAH, which suggests a complete maturation of the digestive system in S. violacea larvae. Total activity from all the different enzyme activities followed the same trend as the specific activity. Based on the results from this study it might be feasible to begin weaning this species at 35 DAH, thereby reducing the amount of live food in the current protocol used which initiates weaning 45 days.

Because of its outstanding biological and industrial importance, many efforts have been made to characterize the mycobiota of new environments and their biochemical and biotechnological potentials. Gut mycobiota can be a source of novel yeasts with the potential to be used as probiotics or have industrial applications. In this work, we characterized two as-yet unexplored yeast communities from the intestinal content of the cultured marine Chilean fishes Genypterus chilensis (G. chilensis) and Seriolella violacea (S. violacea). Yeasts were isolated through culture, identified by sequencing their ITS region, and characterized their enzymatic profile with API®ZYM. Rhodotorula mucilaginosa was identified in both fish species. For the first time, Candida palmioleophila, Candida pseudorugosa, Cystobasidium slooffiae, and a member of the Yamadazyma genus were also identified and described as part of the normal fish gut–microbiota. Furthermore, the diverse enzymatic profile exhibited by some of these isolates suggests that it may be possible to develop novel applications for them, such as new probiotics and other biotechnological applications.

Aquaculture diversification is important for providing sustainable sources of food fish amidst changing environments, pathogens, economies, and market demand. Particularly for newly cultured species where information may be limited, optimization of culture practices relies on an understanding of the physiology and ecology of a species. The cojinoba (Seriolella violacea; Centrolophidae), a coastal pelagic marine fish, is a species of growing importance for aquaculture production in South America. Although methods for breeding and larval to juvenile rearing have been established, little is known about the physiology of this species. Therefore, measures of metabolism, swimming capacity and efficiency, red:white (R:W) muscle ratios, and associated aerobic and anaerobic biochemical parameters, such as plasma glucose and lactate, and muscle enzyme activities (i.e., pyruvate kinase, citrate synthase, electron transport system [ETS]), were measured. For cojinoba at 15 °C with mean body length (BL; total length) of 22 cm, critical swimming velocity (Ucrit) was approximately 80 cm/s or 3.8 BL/s, and optimal swimming velocity (Uopt) was 50 cm/s or 2.3 BL/s. Aerobic scope for metabolism was approximately 300 mg O2/kg/h, with Mo2 max 3.4 fold greater than standard metabolic rate. Swimming was facilitated by linear increases in tail beat frequency until burst and glide swimming initiated near Ucrit. At low velocities, large (~20% BL) pectoral fins were used for propulsion and maneuverability/maintaining equilibrium; beat frequency diminished rapidly with increasing velocity. Red:white muscle ratios at 50% BL and 75% BL (caudal peduncle) were comparable to other ectothermic species, with a greater proportion of red muscle in the caudal peduncle presumably corresponding to facilitation of sustained pelagic swimming. Plasma glucose and lactate were elevated at Ucrit by 20% and 45% respectively, indicating mobilization of anaerobic energy sources at fatigue. Aerobic enzyme activities were much higher in red muscle, the ratio of anaerobic:aerobic enzyme activity was higher in white muscle, and ETS activities decreased at fatigue in both red and white muscle. The cojinoba has a moderate metabolic rate compared to other pelagic species, displays shoaling behavior, is maneuverable at low velocities due to pectoral fin use, but has optimal swimming efficiencies at higher velocities. These factors are beneficial for designing culture systems to promote exercise benefits for growth and welfare.

This report offers a macroscopic and histological description of ulcerative gastric lesions in Humboldt penguins associated with the presence of Contracaecum pelagicum. Parasites of this genus have been isolated from different species of marine mammals and birds, including penguins, demonstrating its capacity to generate ulcerative lesions in the gastrointestinal tracts of many hosts. A bibliographic review revealed no publications on gastric ulceration by nematodes in Humboldt penguins. Studies carried out in Chile concerning gastrointestinal parasitism by nematodes of the Contracaecum genus in S. humboldti only established the parasite's taxonomy. This is the first pathological description of a parasitic ulcerative manifestation in the stomach of S. humboldti in the world. The Humboldt penguin is a vulnerable species. Therefore, this study is relevant as it offers a better understanding of the diseases that affect S. humboldti and facilitates the development of strategies intended to recover the population.

This paper describes and evaluates the mortality associated with the potential stressor effect induced by application of artificial photoperiods in rainbow trout (Oncorhynchus mykiss). After application of artificial photoperiods, high mortalities of trout subjected to this management were recorded (36% in LD 14:10 and 25% in LD 24:0) as compared to controls (7%). The recorded signology related to diseased trout included darkening, lethargy and erratic swimming. Among the morphological changes, skin lesions and ulcerative-type necrosis could be observed. Blood tests, histopathology and isolation of pathogens identified as Flavobacterium psychrophilum, associated with Aeromonas, Pseudomonas and Saprolegnia sp., were performed. The application of artificial photoperiods suggests that fish may be more susceptible to opportunistic diseases; thus, it is advisable to emphasize preventive measures in fish subjected to this management.

En peces, para el control homeostático, se necesita un adecuado suministro de oxígeno desde el medio acuático hasta los sitios de metabolismo aeróbico. Muchos peces están bien adaptados para soportar condiciones hipoxicas en su ambiente por ajustes respiratorios y cardiovasculares. Sin embargo no existe suficiente información sobre la respuesta homeostática de parámetros sanguíneos a hipoxia aguda. En los peces de cultivo es común que ellos sean expuestos a cortos periodos de hipoxia o anoxia a causa de fallas en las rutinas de manejo. Se determinó hematocrito, hemoglobina, recuento de eritrocitos, tamaño de los eritrocitos y cantidad de hemoglobina por eritrocito en truchas (Oncorhynchus mikyss) llevadas a hipoxia progresiva por mantención de los peces en respirómetros estáticos por 5, 10, 20 y 30 minutos; también se determinó el Indice Bazo-Somático (IBS) y la tasa de consumo de oxígeno. Los resultados mostraron que los peces fueron expuestos a condiciones hipoxicas de 2 mg O2/L al final de los 30 minutos. En respuesta al estrés hipoxico las truchas reaccionaron con disminución del consumo de oxigeno y del (IBS) e incrementos simultáneos en el número de eritrocitos, hematocrito y policromatófilos (eritrocitos inmaduros). Sin embargo el tamaño celular y la concentración de hemoglobina en los eritrocitos disminuyeron. Estos resultados sugieren que los peces se adaptan al estrés hipóxico reduciendo el consumo de oxígeno (respuesta oxiconformadora) e incrementando el número de eritrocitos en circulación. Sin embargo muchas de estas células son fisiológicamente poco funcionales debido a la poca hemoglobina que poseen An adequate transfer of oxygen from the aquatic environment to the oxidative sites at fish tissues is needed to supply the methabolic requeriments for the homeostatic control. Many fish are well adapted to survive hipoxic conditions in their environments by respiratory and cardiovascular adjustments. However, there are not sufficient information on the homeostatic responses in blood parameters to acute hipoxia. In fish aquacultures, it is common that fishes are exposed to short periods of hypoxia or anoxia because failing in the management routines. To examine the physiological responses in the blood comparment to short-time increasing hypoxic conditions, laboratory experiments were done with rainbow trout (Oncorhynchus mikyss). Blood parameters assessed were hematocrit, hemoglobin concentration, erythrocyte total number, erythrocyte size and hemoglobin content in red cells, together wih fish oxygen consumption and variations in the Somatic-Spleen Index (IBS). Fish were exposed to increasing hypoxic conditions (0, 5, 10, 20 and 30 minutes) inside glass-sealed respirometers. The results showed that fish were exposed to hypoxic conditions as such as 2 mg O2/lt at the end of 30 minutes. In response to the hypoxic stress, trouts showed diminished oxygen consumption together with a decreasing IBS with simultaneous increasing values in number of erythrocytes, hematocrite and poly-chromatophils red cells. However, cellular size and hemoglobin content in the red cells, were decreased. These results suggest that stressed fish adapted to increasing hypoxic conditions with reduction in the oxygen consumption (oxyconformation response) and increasing number of red cells in blood circulation. However most of the red cells were physiological non-functional since the on hemoglobin contents did not increase with hypoxia