Nile tilapia (Oreochromis niloticus) is one of the most important commercial freshwater fish in China, and dietary transition occurs in their different life stages. The gut microbiota is important to host health. The relationships among the diet, gut microbiota, and development of tilapia are not well known. In the present study, we attempted to understand how diet is associated with microbiota community dynamics during the development of tilapia. The first experiment was performed under standard laboratory feeding operation to determine the effect of diet transition on intestinal microbiota. In the second experiment, tilapia were fed with Artemia or plant-based dry (PBD) food from the fish started feeding to their late juvenile stage (90 days post-fertilization). The results in the first experiment showed that feeding habit transition in juvenile fish had a low effect on the microbiota of the tilapia intestine. In the second experiment, plant-based food negatively affected the survival rate and intestinal development of tilapia. The phylum Planctomycetes was dominant in juvenile fish fed PBD food. The phylum Fusobacteria was dominant in the juvenile fish fed Artemia. At the genus level, Gemmobacter, Pirellula, and Planctomyces, belonging to the phylum Planctomycetes, were significantly abundant in the guts of fish fed the PBD food diet. Cetobacterium of the phylum Fusobacteria was dominant in juvenile fish fed Artemia. Thus, we can conclude that diet types have a great effect on the microbiota of tilapia intestine in their early life stages. The intestinal microflora of tilapia was established in juvenile tilapia, approximately 2 months after hatching. Our results provide useful information for the experimental design of studies on the microbial community of the tilapia gut. We suggest that modulation of gut microbiota of tilapia could be performed in their early life.

The light spectrum is a vital environmental factor for the culture of fish, and the welfare of farmed fish is a crucial issue in aquaculture. In this study, Nile tilapia (Oreochromis niloticus, GIFT strain) juveniles were exposed to full-spectrum (LW), red (LR), yellow (LY), or blue (LB) light. After the 45-day experiment, growth performance, stress responses, and aggressive behaviors were evaluated, and transcriptomic analysis was carried out. The results revealed that LW and LR positively affected growth performance. At the same time, LY and LB had a negative effect. Light spectrum induced stress responses of juvenile fish exposed to LY, under which the total antioxidant capacity (T-AOC) and cortisol (COR) contents were the highest. The activities of α-amylase (AMS), protease (PES), and lipase (LPS) in the digestive tract showed a similar tendency, indicating that the light spectra altered the digestive enzyme activities and then affected growth. Behavioral analyses showed increased chase and bite activities of tilapia juveniles exposed to LW and LY. The affected functions included the nervous system, muscle morphogenesis, and immune system-related regulation. Enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways include the tryptophan metabolism signaling pathway, protein digestion and absorption signaling pathway, Jak-STAT signaling pathway, arachidonic acid metabolism signaling pathway, and alpha-linolenic acid metabolism signaling pathway. Overall, light spectra influenced the welfare of farmed tilapia juveniles in terms of growth, stress, and behavior. Our results suggested that LR should be used in juvenile tilapia culture.

Gasterophilosis is a significant threat to equids in the desert steppe of X injiang, C hina, where G asterophilus pecorum ( F abricius) ( D iptera: G asterophilidae) is the dominant botfly species. A population analysis was conducted on 195 individual G . pecorum larvae from three host species, P rzewalski's horse, the domestic horse and the A siatic wild ass. The distribution of haplotypes of the maternally inherited mitochondrial cytochrome oxidase subunit I ( COI ) gene was analysed to assess the population differentiation of G . pecorum . High haplotype diversity was observed among G . pecorum populations from all host species, indicating that the G . pecorum infecting one host had multiple maternal ancestors. A phylogenetic tree showed six clades, suggesting a high degree of genetic differentiation. A constructed haplotype network described both the origin of the haplotypes and the population structure. The findings indicated that G . pecorum infections within P rzewalski's horses were mainly transmitted from A siatic wild asses. Clade 1 was found to be the most primitive group and to have evolved to be highly adaptable to the desert steppe. Clade 2 originated from C lade 1, potentially as a result of the annual migration of domestic horses. Revealing the differentiation of the G . pecorum population is important for elucidating the aetiology of G asterophilus infection in X injiang and for planning appropriate control measures.

In the present study, we investigated the effect of probiotics immobilized by oyster shells (Os), vesuvianite (Ve) and walnut shells (Ws) on the remediation of aquaculture water and sediment by analyzing the variation of ammonia-nitrogen (NH4–N), nitrate-nitrogen (NO3–N), nitrite-nitrogen (NO2–N), total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (CODCr), as well as the microbiota of the water and sediment. The positive or negative effects of the treatment groups on the water quality parameters were both observed. Compared with their effects on water quality parameters, the treatment groups had better effects on sediment parameters. Group Ve had the best remediation effect of NH4–N and NO3–N in the sediment (decreased by 5.22 and 1.66 times, respectively). Group Os showed a lower relative concentration of TN and CODCr (decreased by 3.77 and 0.95 times, respectively). The high-throughput sequencing results revealed that the immobilized probiotics increased the relative abundances of functional bacteria in the treatment groups at the phylum and genus level. The above results showed that probiotics immobilized by oyster shells, vesuvianite and walnut shells positively affected the aquaculture environment's remediation, especially the sediment.