Loss of gut microbial diversity in the cultured, agastric fish, Mexican pike silverside (Chirostoma estor: Atherinopsidae).

Teleost fish are the most diverse group of extant vertebrates and have varied digestive anatomical structures and strategies, suggesting they also possess an array of different host-microbiota interactions. Differences in fish gut microbiota have been shown to affect host development, the process of gut colonization, and the outcomes of gene-environment or immune system-microbiota interactions. There is generally a lack of studies on the digestive mechanisms and microbiota of agastric short-intestine fish however, meaning that we do not understand how changes in gut microbial diversity might influence the health of these types of fish. To help fill these gaps in knowledge, we decided to study the Mexican pike silverside (Chirostoma estor) which has a simplified alimentary canal (agastric, short-intestine, 0.7 gut relative length) to observe the diversity and metabolic potential of its intestinal microbiota. We characterized gut microbial populations using high-throughput sequencing of the V3 region in bacterial 16S rRNA genes while searching for population shifts resulting associated with fish development in different environments and cultivation methods. Microbiota samples were taken from the digesta, anterior and posterior intestine (the three different intestinal components) of fish that grew wild in a lake, that were cultivated in indoor tanks, or that were raised in outdoor ponds. Gut microbial diversity was significantly higher in wild fish than in cultivated fish, suggesting a loss of diversity when fish are raised in controlled environments. The most abundant phyla observed in these experiments were Firmicutes and Proteobacteria, particularly of the genera Mycoplasma, Staphylococcus, Spiroplasma, and Aeromonas. Of the 14,161 OTUs observed in this experiment, 133 were found in all groups, and 17 of these, belonging to Acinetobacter, Aeromonas, Pseudomonas, and Spiroplasma genera, were found in all samples suggesting the existence of a core C. estor microbiome. Functional metagenomic prediction of bacterial ecological functions using PICRUSt2 suggested that different intestinal components select for functionally distinct microbial populations with variation in pathways related to the metabolism of amino acids, vitamins, cofactors, and energy. Our results provide, for the first time, information on the bacterial populations present in an agastric, short-gut teleost with commercial potential and show that controlled cultivation of this fish reduces the diversity of its intestinal microbiota.

Cannibalism rate and mLeptin expression are influenced by photoperiod and diets in Piracanjuba, Brycon orbignyanus (Valenciennes, 1850) larvae.

Piracanjuba (Brycon orbignyanus) is a species with great productive potential, and during its larval phase, it presents intense cannibal activity. The photoperiod and diet are primary feed behaviour and cannibalism modulators to fishes. This experiment aimed to verify the effect of different photoperiods and diets in Piracanjuba larviculture. Larvae were kept under different photoperiods - 12 h light: 12 h dark (12 L: 12D); 24 h light:00 h dark (24hL: 00D) - Larvae were fed with Artemia nauplii and a formulated micro-diet in a factorial scheme for 10 days, and at the end of the experimental period, the influences of the treatments on performance and quantitative expression of mLeptin and mBmall1 were evaluated. In order to quantify the expression of mLeptin and mBmall1, qPCR adopting ß-actin and Elongation Factor 1 as endogenous genes was used. The primers for all the analysed transcripts were obtained through multiple sequences alignments of different fish species. It was observed that the diet and photoperiod influence the performance of Piracanjuba (B. orbignyanus) larvae in the initial phase of larviculture. Feeding with artemia nauplii and the photoperiod of 24 L:00D reduce cannibalism rates in intensive Piracanjuba larviculture. The results on the rate of cannibalism, rate of survival and the relative expression of mLeptin are related to the survival rate of the larvae, and it is inversely proportional to the cannibalism rate. The expression levels of mBmall1 showed a correlation with the final weight of the larvae. Piracanjuba Larvae under a photoperiod of 24 light and fed Artemia nauplii showed more significant levels of mLeptin expression.

Sperm characterization and cryopreservation of the endangered freshwater fish Chirostoma estor (Atheriniformes).

The knowledge of the physiology of sperm of an endangered species allows the implantation of reproductive biotechnologies that aim at conservation. The aim of this study was to characterize fresh sperm and evaluate different cryopreservation solutions for sperm in Chirostoma estor. The characterization of Chirostoma estor fresh sperm (n = 22 males) was performed through analyzes of sperm concentration, membrane integrity, sperm morphology, motility rate, motility quality score, and motility duration. For cryopreservation (n = 42 males), 3 extenders (BTS™, MIII™, or Androstar Plus™) in combination with 2 permeable cryoprotectants (dimethyl sulfoxide (DMSO) or methyl glycol (Methyl)) were used. Analyzes of post-thaw sperm were performed as described for fresh sperm and additionally the fertilization rate analysis was performed. Fresh sperm presented a sperm concentration of 29.2 × 109 spermatozoa/mL, membrane integrity of 82.4%, and morphologically normal cells of 53%. After glucose activation (150 mM) a motility rate of 87.5%, sperm quality score of 5.0, and a duration of motility of 285 s were observed. For post-thaw sperm, MIII + Methyl and Androstar + Methyl solutions resulted in the highest motility rates of 40-48%. No differences were observed for motility duration, membrane integrity, and sperm morphology. Samples cryopreserved in Methyl (12-20%) showed a higher fertilization rate than DMSO, independently of the extender. In conclusion, the fresh sperm collected artificially from Chirostoma estor presents a compatible quality to carry out fertilization and can be cryopreserved in the commercial extenders MIII™ and Androstar Plus™ together with the cryoprotectant Methyl glycol.