Activin A affects feeding by promoting the inner diameter and muscle development of the pharynx and oesophagus in zebrafish (Danio rerio) larvae

Barbatula nuda: an economically valuable freshwater fish that accepts phytoplankton as first food

Barbatula nuda is considered a promising emerging species to diversify small cold-water fish aquaculture worldwide due to its rapid growth and delicious flesh. However, limited information on larval development and nutrition is available. In this study, 7-day feeding experiments were performed to evaluate three different initial diets (zooplankton, phytoplankton, and artificial microdiet) in the zoo group, algae group, and AD group on growth, development, and digestion of larvae B. nuda. The results showed that there was no significant difference in survival rate among the three groups (p > 0.05). The algae group exhibited the highest feed intake success rate and body weight (p < 0.05), the best intestinal development with the protruded intestinal mucosa, and visible intestinal microvillus. Pepsase and trypsin enzyme activities in the algae group larvae were significantly higher than those in the other two groups (p < 0.05). Transcriptome data showed that the mechanistic target of rapamycin pathway of B. nuda fed with phytoplankton was activated, and the metabolisms of carbohydrate were significantly more active than those in the other two groups. As omnivorous fish, B. nuda could accept zooplankton, phytoplankton, and microdiet as initial diets with its survival unaffected, but B. nuda fed with phytoplankton exhibited better growth status and digestive tract development and higher digestive enzyme activities than those fed with other two diets. Therefore, phytoplankton was a suitable initial diet for B. nuda. Our findings provide guidance for the artificial breeding of B. nuda and a theoretical basis for research on fish initial diet.

Genome-wide identification and expression patterns of opsin genes during larval development in Chinese perch (Siniperca chuatsi)

Vision is important for fish to forage food and fishes express opsin genes to receive visual signals. Chinese perch (Siniperca chuatsi) larvae prey on other fish species larvae at firstfeeding but donoteat any zooplankton, the expression of opsin genes in S. chuatsilarvae is unknown. In this study, we conducted a whole-genome analysis and demonstrated that S. chuatsihave5cone opsin genes (sws1, sws2Aα, sws2Aβ, rh2and lws)and 2 rod opsin genes (rh1and rh1-exorh). The syntenicanalysisshowedthe flanking genes ofall opsin genes were conserved during fish evolution, but the ancestorof S. chuatsimightlost some opsin gene copies duringtheevolution.The phylogeneticanalysisshowed sws1of S. chuatsiwas closest to those of Lates calcariferwhich had a truncated sws1gene; the sws2Aα, sws2Aβ,lws,rh2,rh1 andrh1-exorh of S. chuatsihad a closer relationship with those of Percomorpha fishes.Importantly, results of in situhybridization showed the sws1 opsingene,which is related to forage zooplankton,had extremely low levelexpression in retinaat early stages.Surprisingly, the rh2 opsin gene had a high level expression at firstfeeding stage. The sws2Aα, sws2Aβand lwshad a little expression at early stages but the lwsshowed a increasing trend with larval development, rh1 opsin gene expression appeared at15 dph. In thisstudy, we found a specialpattern of visual opsin genes expression in S. chuatsi, it might influence the larval first feeding and feeding habit.