Aquaculture Research

Nutrition, disease, and general wellbeing can be affected by the microbial communities associated with the digestive tracts of aquaculture species. Different sections of aquaculture species’ digestive tracts have distinctive surfaces and structures, which can change microbial communities. The present study examined the composition and distribution of bacterial species in the intestine of hybrid grouper (Epinephelus fuscoguttatus E. polyphekadion) and its aquaculture environment. Using high-throughput pyrosequencing, a 16S rRNA sequence analysis was performed on hybrid grouper foregut, midgut, and hindgut, as well as cultured water and feed. There were 610,452 sequences obtained from five components (foregut, midgut, hindgut, water, and feed). Among operational taxa (OTUs), 506 of them were detected in the foregut, 605 in the midgut, 510 in the hindgut, and 573 in aquaculture water and feed samples. A total of 113 were detected in 5 samples. A species annotation revealed that hybrid grouper intestinal tracts were dominated by Proteobacteria (67.3%–73.7%), Firmicutes (8.4%–14.0%), and Actinobacteria (6.9%–10.5%). In aquaculture culture water, Proteobacteria were predominant (36.3%), Actinobacteria (30.0%), and Planctomycetes (14.0%). Acinetobacter (1.4%–17.9%) and Photobacterium (32.0%–57.5%) dominated the intestine. Photobacterium (3.6%) and Mycobacterium (7.1%) dominated the water bacteria. The water and intestine contained five potentially pathogenic bacteria: Pseudomonas, Flavobacterium, Escherichia coli, Aeromonas bacteria, and Vibrio. The highest proportion of Vibrio was found in the water (1.7%), while Pseudomonas dominated the midgut (2.6%). Six potential probiotics were detected in the aquaculture water and intestine (Lactococcus, Streptococcus, Bdellovibrio, Lactobacillus, Bacillus, and Bacteroides). Aquaculture water and intestines contained Bacillus, Bacteroides, and Lactobacillus. According to the findings, the intestinal flora of hybrid grouper is closely correlated with its pond culture environment. Results from the study provide an experimental basis for the controlled breeding of hybrid groupers and the regulation of their microecological processes in the breeding environment deepen our understanding of the intestinal bacterial population of healthy hybrid groupers.

The present study was conducted on the Nile tilapia (Oreochromis niloticus) and screened for single nucleotide polymorphisms (SNPs) in the muscle hormone genes myogenin (MyoG) and myostatin (MSTN). Samples were collected from the JangHang fish farm and categorized by body weight and sex. The average total weight was 1.02 kg for the 82 males and 0.63 kg for the 70 females. A body weight in the range of the average weight ±10% was considered as normal weight. Target regions of each gene were categorized, such as the promoter region, 5′-untranslated region (5′UTR) and 3′UTR. Genomic deoxyribonucleic acid (gDNA) was extracted, amplified, sequenced, aligned, and screened for the presence of nucleotide variations. Three SNPs, 1,875T>A, 1,892C>T, and 1,946A>G, and one insertion (TGA​CAT​ATT​TCC​CTC​ACA) at 2,138–2,145 were detected in the 3′UTR of the MyoG gene. However, within the MSTN gene, one insertion at 450 (T) and two SNPs at 536 (G>A and A>A) were found in the 5′UTR. In addition, four insertions at 1,278–1,279 (GT, T, TGT, and G) and one short tandem repeat (STR) at 1,129 (TG) in Exon 1, two SNPs at 4,438 (3′UTR; A>C and C>C), and two SNPs at 4,514 (3′UTR; G>A and A>A) were identified. Principal component analysis (PCA) and statistical analyses were performed to evaluate the relationships between the SNPs and body weight, forming 6 and 41 genotype blocks in the MyoG and MSTN genes, respectively. We found significant correlations between the SNPs and body weight traits for the effective genotype blocks GBG-1, GBG-3, and GBG-4 of MyoG and GBN-1, GBN-2, GBN-3, GBN-4, GBN-13, GBN-22, and GBN-24 of MSTN. These outcomes would be significant for fish breeding and may help obtain data for use in genetic marker kits. In some instances, genetic marker kits have a distinct advantage for improvement in genetics, parentage control, identification of species, and enhancing breeding stock and its applications in aquaculture.

To identify the optimal stocking rate of Micropterus salmoides culture in a land-based round pond recirculating aquaculture system, five stocking densities were tested, i.e., D1–D5 with 60, 70, 80, 90, and 100 fish/m², respectively. The water temperature of the experimental pond was 20.0–26.5°C. The effects of stocking density on culture productivity and physiological indexes of M. salmoides (initial body weight 50.83 ± 7.28 g) were examined. The D1 and D5 treatments exhibited significantly improved growth performance. The population weight gain in the D5 treatment was the highest, which increased by 63.73%, 52.82%, 60.93%, and 45.08%, compared with groups D1–D4 (, each), and the feed conversion ratio was the lowest, which was decreased by 5.65%, 12.03%, 26.42%, and 21.48% compared with groups D1–D4. The levels of crude protein, essential amino acids, and total free amino acids in muscle tissue of group D3 were higher than those in the other groups. Stocking density did not differ significantly on muscle fatty acid composition , each). The activities of serum AKP and LZM and liver SOD, AKP, and LZM in group D5 were significantly higher than those in the other groups. Thus, 100 fish/m² was the optimal stocking density of M. salmoides at a size stage of 50.83∼130.13 g in the circulating water of land-based round ponds.

Understanding the effects of environmental parameters on the reproductive cycle of shellfish is an essential tool for successful hatchery conditioning management and, consequently, for seed supply to the industry. For the tropical oyster, Crassostrea tulipa, little is known about the factors affecting the maturation process and reproduction, but there are indications that salinity may be of importance. Two experiments were carried out to evaluate the effects of salinity on the reproductive cycle of broodstock of C. tulipa. In the first experiment, oysters were reared in five salinities (40, 35, 30, 25, and 20) for 40 days and gonad histological samples were collected regularly. In a follow up experiment, oysters were reared in variable salinity conditions changing from 40 to 30 or from 20 to 30 over a period of 40 days. Salinity was found to affect the reproductive cycle of C. tulipa. Oysters kept in constant salinity of 30 showed a higher condition index compared to animals in other salinities, with most of the animals in the prespawning stage. Salinity variation was also shown to affect C. tulipa maturation. The prespawning stage was the most observed reproductive stage in low salinity, and high salinity induced a resting stage in the female animals. The results are considered the first step towards developing a protocol for the conditioning of C. tulipa in hatchery conditions.

Habitat space is crucial for animals. This experiment explored the effect of four different farming acreages (0.5 m², 1 m², 10 m², and 100 m²) on survival rate, growth performance, and muscle nutrition composition of swimming crabs (Portunus trituberculatus) at the farming density of 2 ind/m². The results showed that the survival rate of the crabs that live in the 10 m² group and live in 0.5 m² alone had the highest survival rate of 20.50% and 20%, better than the 1 m² group and the 100 m² group with the lowest of 12.00% and 13% (). There was no significant difference between final body weight and final carapace width among the 4 groups (). The crude lipid content was the highest in 1 m², which was significantly higher than in 0.5 m² (). The crude protein content in the 1 m² and 10 m² groups was significantly higher than that in the 0.5 m² and 100 m² groups (). The results of the three conventional nutrients showed that there was no positive correlation between the muscle conventional nutrients and the farming area. The polyunsaturated fatty acid part of the 100 m² and 10 m² group was significantly different from the 1 m² and 0.5 m² groups (). The results show that farming crab alone is not better than together, and a small aquaculture acreage helps to improve the muscle nutrition composition of the swimming crabs, while a large aquaculture acreage is more conducive to balance the development of nutrition. Overall, 10 m² of habitat space was more economically feasible in practice.

Carbohydrates are commonly used in aquaculture feed because they are the cheapest energy source. Promoting carbohydrate catabolism for energy production can increase the dietary protein utilization efficiency (i.e., a protein-sparing effect). Alpha-lipoic acid (α-LA) is a cofactor of some rate-limiting key enzymes (pyruvate dehydrogenase complex and α-ketoglutarate dehydrogenase) in carbohydrate metabolism. To determine whether α-LA could promote carbohydrate catabolism to have a protein-sparing effect, we investigated the growth, activities of key enzymes involved in carbohydrate metabolism, transcript levels of genes encoding enzymes involved in energy metabolism, and the hepatopancreas structure of Macrobrachium nipponense fed with diets containing different protein/carbohydrate ratios (P/C) with and without α-LA. Six experimental diets for M. nipponense were formulated with casein and fish meal as the protein sources, fish oil and soybean oil as the lipid sources, and corn starch as the carbohydrate source. The six diets consisted of three different P/Cs (, , and ) without or with α-LA (at 1300 mg/kg). Each diet had six replicates and was fed to prawns (initial weight 0.110 ± 0.010 g) twice daily to apparent satiation. Dietary supplementation with α-LA significantly increased the survival rate of prawns, regardless of the P/C ratio. In the low-P/C group (), the weight gain did not vary between those that consumed α-LA and those that did not. The P/C ratio and α-LA significantly affected the activities of key enzymes involved in glycolysis and the citric acid cycle. In the group, the hexokinase (HK) and pyruvate dehydrogenase (PDH) activities were significantly higher in prawns that consumed α-LA than in those that did not. In both the and groups, the pyruvate kinase (PK) activity was significantly higher in prawns that consumed α-LA than in those that did not. Significant interactions between P/C and α-LA were found for the transcript levels of genes encoding adenine ribonucleotide-dependent protein kinase subunits (AMPK αand AMPK β), HK, glucose-6-phosphate dehydrogenase (G6PDH), acetyl-CoA carboxylase (ACC), and fatty acid binding protein 10 (FABP 10), all of which are involved in energy metabolism. In the low-P/C group, α-LA increased the transcript levels of genes encoding AMPK α, AMPK β, HK, phosphoenolpyruvate carboxykinase (PEPCK), G6PDH, and MDH, decreased the transcript level of the gene encoding ACC, and did not affect the transcript levels of genes encoding FABP10 and palmitoyl transferase 1 (CPT1). The P/C ratio and α-LA did not affect the overall morphology of the hepatopancreas, but at a low P/C, dietary supplementation of α-LA increased the number of hepatopancreatic B cells. In conclusion, supplementation with α-LA at 1300 mg/kg in a low-P/C diet of M. nipponense increased its carbohydrate utilization efficiency, energy metabolism, and the number of hepatopancreas B cells, thereby having a protein-sparing effect.