Aquaculture encounters significant challenges due to diseases caused by pathogenic microorganisms. At the microbiological level, the primary culprits are fungi, bacteria, and parasites that can affect the microflora residing on and within the skin, gills, opercula, and digestive tract of the fish, potentially leading to chronic diseases or death. Recently, initiatives have been proposed for the development of mullet (Mugilidae) farming, and Colombia has not been an exception. At the University of Magdalena (Magdalena, Col.), progress has been made in their domestication and artificial reproduction; however, during the domestication process, certain characteristics have emerged that indicate contamination by yet undetermined pathogenic microorganisms, which manifest in the fish through signs of laceration or petechiae possibly associated with bacterial or fungal pathologies. Thus, the objective of this study was to identify microorganisms present in the smooth areas that exhibited wounds or petechiae in the operculum region and in cultivation tanks of mullet (Mugil incilis) raised in the laboratory. To achieve this, the swabbing technique was employed using saline solution tubes to collect representative samples through swabs, from both culture tanks and the fish. Samples (1ml) were inoculated onto Plate Count Agar (PC) at 35°C for 24 hours and Sabouraud Agar (SB) at 29°C for 120 hours. Following selection and purification, microscopic characterization of the strains was performed using Gram staining and lactophenol blue. A total of 8 bacterial strains and 8 fungal strains were isolated. After successive reseeding, 4 bacterial strains were obtained from the samples taken from the culture tanks, along with 4 bacteria from the operculum of the fish, and 7 fungal strains. Morphological identification revealed the presence of both Gram-positive and Gram-negative cocci. Among the isolated bacteria, Gram-positive cocci were the most prevalent, while the identified fungi included Aspergillus spp. (the most frequently isolated), Alternaria spp., and Penicillium spp. (see Table 1). Although the presence of bacteria was not significant, they may pose potential infectious risks, whereas the fungi could act as opportunistic agents or highly invasive pathogens in fish, leading to severe diseases or mortality. The presence of these microorganisms in the cultures is attributed to factors such as water quality, high population density, poor nutritional status, stress, among others. It is likely that, being wild species adapted to captivity, they are more susceptible to acquiring diseases or are more fragile, thus necessitating an increase in preventive measures and animal health efforts in the cultures.
This research was funded by Project BPIN 2021000100084 titled: "Fortalecimiento de las capacidades institucionales para la investigación del cultivo y reproducción inducida de la lisa (Mugil incilis) como una alternativa para su conservación en el Caribe Colombiano, Magdalena" supported by the Ministry of Science, Technology, and Innovation of Colombia (MINCIENCIAS- Regalías).