RESUMO
Comprehending the immune defense mechanisms of new aquaculture species, such as the Chilean meagre (Cilus gilberti), is essential for sustaining large-scale production. Two bioassays were conducted to assess the impact of acute and intermittent hypoxia on the antibacterial activity of juvenile Chilean meagre epidermal mucus against the potential pathogens Vibrio anguillarum and Vibrio ordalii. Lysozyme and peroxidase activities were also measured. In general, fish exposed to hypoxia showed a 9-30% reduction in mucus antibacterial activity at the end of hypoxic periods and after stimulation with lipopolysaccharide. However, following water reoxygenation, the activity of non-stimulated fish was comparable to that of fish in normoxic conditions, inhibiting bacterial growth by 35-52%. In the case of fish exposed to chronic hypoxia, the response against V. anguillarum increased by an additional 19.8% after 6 days of control inoculation. Lysozyme exhibited a similar pattern, while no modulation of peroxidase activity was detected post-hypoxia. These results highlight the resilience of C. gilberti to dissolved oxygen fluctuations and contribute to understanding the potential of mucus in maintaining the health of cultured fish and the development of future control strategies.
RESUMO
Las características anatómicas e histológicas del tracto alimentario de la merluza austral (Merluccius australis) se han estudiado con el fin de comprender la fisiología digestiva y formular alimentos balanceados adecuados. M. australis posee un esófago corto, un estómago en forma de y grande y un intestino corto. Histológicamente, el tracto digestivo está formado por cuatro capas: la mucosa, submucosa, muscularis y la serosa. El esófago es un órgano tubular corto de pared gruesa con una gran capacidad de distensión y abundantes células caliciformes secretoras de mucus que permite el paso de grandes presas. El estómago es grande y musculoso, con alta capacidad de distensión. No se observo la presencia de apéndices pilóricos. El intestino es corto y dividido en regiones: proximal, medio y distal. En la región anterior del intestino se observaron abundantes células caliciformes, que disminuyeron en la región media para finalmente dispersarse en la región posterior. Además, los enterocitos mostraron un aumento en la presencia de vacuolas supranuclear en la región posterior del intestino. Los resultados de este estudio anatómico e histológico indican que M. australis tiene un sistema digestivo similar a otros peces gadiformes, el cual está adaptado para digerir y absorber presas ricas en proteínas, principalmente pescados y crustáceos.
The anatomy and histology features of alimentary tract of southern hake (Merluccius australis) have been studied in order to understand the digestive physiology and formulate suitable feeds. M. australis has a short oesophagus, large y-shaped stomach and short intestine, and histologically, the digestive tract is formed by four layers: mucosa, submucosa, muscularis and serosa. The oesophagus is a short tubular thick-walled organ with a great distension capacity and abundant mucus secreting goblet cells allowing the passage of large preys. The stomach is large and muscular with high capability for distension. Pyloric caeca were not present. The intestine is short and divided into a proximal middle and distal segment. In the anterior region of the intestine was observed abundant goblet cells, which decreased in the middle region and finally dispersed in the posterior region. Additionally, enterocytes showed an increase in the presence of supranuclear vacuoles at the posterior region of the intestine. The results of this anatomical and histological study indicate that M. australis has a digestive tract similar to other gadiform fishes, which is adapted to digest and absorb protein-rich preys, mainly fish and crustacean.