Histopatología de juveniles cultivados de Totoaba macdonaldi asociados con aislamientos bacterianos identificados molecularmente como Vibrio spp. durante un evento de aumento de temperatura

Abstract

Totoaba macdonaldi is an endangered species of croaker endemic to the Gulf of California, Mexico. This species has been cultured for the repopulation of wild stocks and commercialization at the Wildlife Management and Conservation Unit for the culture of T. macdonaldi at the Universidad Autónoma de Baja California, Mexico. A mortality episode was observed in 50 day-old juveniles, that coincided with an increase of temperature from 16 to 25.5˚C that affected the aquaculture facility. Histopathological and bacteriological analysis of survivor fishes were conducted to investigate the possible causes of mortality. Gill damage including severe congestion in gill filaments, necrosis, and epithelial dissociation of lamellae were observed. Moreover, epidermal, hypodermic necrosis, as well as diffuse bacterial colonization of the dermis was detected. Severe congestion and hemolysis were detected in the heart’s atrium and hepatic portal vessels. From the skin lesions, eight colonies of bacteria were isolated, these corresponded to four species of genus Vibrio, tentatively identified by partial sequence of the 16S rRNA gene as Vibrio harveyi, V. rotiferianus, V. brasilensis and V. shilonii. From them, V. harveyi corresponded to 4 of the 8 isolates and was found in all moribund fishes. Characteristics of the tissue alterations related with these opportunistic Vibrio spp. suggest an acute mortality event favoured by a temperature increase. This is the first record of the histopathology of T. macdonaldi juveniles that suffered an unusual mortality event under an increase of temperature in cultured conditions associated with Vibrio spp.