Streptococcosis in tilapia Oreochromis sp. is possibly the most important bacterial disease for fish production worldwide. In Colombia, streptococcosis is caused by Streptococcus agalactiae (GBS), but in other countries, Streptococcus iniae is also involved. Prevention of streptococcosis is required and must be addressed for economic, social, international trade and public health reasons. This research used an in vitro culture of tilapia intestine to detail the intestinal mucosal response once the pathogen contacts the epithelium. We show that S. agalactiae sheds off its capsule to adhere to the epithelium. The bacterium adheres as a single individuum, in groups or in chains and is able to divide on the apical border of enterocytes. GBS adheres at and invades exclusively through the apical portion of the intestinal folds, using the transepithelial route. Once within the cytoplasm of enterocytes, the bacteria continue to divide. On the basolateral side of the epithelium, the microorganisms leave the cells to reach the propria and travel through the microcirculation. No evidence of an immuno‐inflammatory reaction or goblet cell response in the epithelium or the lamina propria was seen during the process of adherence and invasion of the pathogen.

Weissellosis is an emergent disease caused by Weissella, a Gram-positive bacteria correlated with hemorrhagic illness and mortality in farm-raised trout in several countries. The current study reports the first outbreaks of weissellosis by Weissella ceti in rainbow trout (Oncorhynchus mykiss), which caused severe mortalities in trout farms in Colombia between May 2016 to June 2019. The disease occurred in several farms irrigated by the same river where temperatures were above 17 °C. Symptoms of the disease were limited almost exclusively to trout above 250 g. The clinical signs consisted of lethargic and anorexic fish, swimming in circles at the surface or against the walls. Pathological findings were mainly ocular lesions like bilateral exophthalmia, periocular and intraocular hemorrhage, lenticular opacity and corneal rupture usually leading to blindness, muscular hemorrhages and necrosis. Microbial isolating from eye, brain, kidney, liver and muscle was performed and W. ceti was confirmed by amplification and sequencing of the 16S rRNA. The aim of this work was to characterize the Weisellosis by Weissella ceti in trouts in Colombia, including microbiological isolating, molecular analysis, gross and microscopic characterization.

We report the first draft genome assembly for Prochilodus magdalenae, the leading representative species of the Prochilodontidae family in Colombia. This 1.2-Gb assembly, with a GC content of 42.0% and a repetitive content of around 31.0%, is in the range of previously reported characid species genomes. Annotation identified 34,725 nuclear genes, and BUSCO completeness value was 94.9%. Gene ontology and primary metabolic pathway annotations indicate similar gene profiles for P. magdalenae and the closest species with annotated genomes: blind cave fish (Astyanax mexicanus) and red piranha (Pygocentrus nattereri). A comparative analysis showed similar genome traits to other characid species. The fully sequenced and annotated mitochondrial genome reproduces the taxonomic classification of P. magdalenae and confirms the low mitochondrial genetic divergence inside the Prochilodus genus. Phylogenomic analysis, using nuclear single-copy orthologous genes, also confirmed the evolutionary position of the species. This genome assembly provides a high-resolution genetic resource for sustainable P. magdalenae management in Colombia and, as the first genome assembly for the Prochilodontidae family, will contribute to fish genomics throughout South America.

Background The bocachico (Prochilodus magdalenae) is a migratory freshwater fish and one of the main species of Colombian continental fishery. Interest in it is due to the fish’s excellent reproductive characteristics and sociocultural value in its native region. As part of native fish species repopulation programs carried out by the GIPEN research group of the San Silvestre fish farm and ISAGEN, the present study aimed to characterize the embryogenesis and early larval development of bocachico from zygote phase to the exogenous feeding period, using morphological and histological landmarks. Results Embryos were obtained by fertilization from hormonally induced, wild-caught brood stock, and subsequent development was monitored at temperatures coinciding with native conditions. Embryonic development from fertilization to hatch lasted 13 h. This included the following stages: zygote, cleavage, blastula, gastrula, segmentation and organogenesis, pharyngula and hatching. Larvae emerged with unpigmented eyes; the cephalic area and the eye primordium were more developed at 1 day post-hatching. At 2–3 days post-hatching, the somites formed myotomes and pharyngeal arches were present as well as an undifferentiated digestive tract (endogenous feeding period). At 3–4 days post-hatching, the mouth was open, and the oral valve was developed; the mouth was continuous with the esophagus and the rest of the digestive system (beginning of the endo–exogenous feeding period). The yolk was observed for up to 9 days post-hatching (end of the endo–exogenous feeding period and beginning of the exogenous feeding period). Conclusion To the best of our knowledge, this is the most comprehensive analysis made of the development of the bocachico to date, from early embryonic development to the larval phase, and this research will contribute to improving the knowledge of the developmental intervals of this species, the critical stages in feeding phases, as well as a more concrete approximation of when the fish is suitable for repopulation based on its morphological development.