The mud crab, Scylla paramamosain, has abundant nutrients in the ovary, where numerous lipids accumulate during ovarian maturation. However, the mechanism behind the accumulation of lipids in the ovary of mud crab during ovarian maturation is largely unknown. This study conducted a comparative transcriptome analysis of the ovaries of mud crabs at various stages of ovarian maturation. A total of 63.69 Gb of clean data was obtained, with a Q30 of 93.34%, and 81,893 unigenes were identified, including 10,996 differentially expressed genes (DEGs). After KEGG enrichment of these DEGs, MAPK signaling pathway was significantly enriched during vitellogenesis. Moreover, the expression levels of genes involved in carbohydrate, amino acid, and lipid metabolism were found to be higher during vitellogenesis. The two genes (Sp-Eip75B and Sp-Eip78C) that are homologous to the vertebrate gene PPARγ in the PPAR signaling pathway, were identified. Additionally, genes in MAPK signaling pathway might regulate lipid metabolism through PPAR signaling pathway based on Protein-Protein Interaction (PPI) network. These findings suggest that MAPK signaling pathway plays a critical role in lipid metabolism in the ovary during vitellogenesis, which provides new insights into the mechanism of lipid accumulation during ovarian maturation in mud crabs.

Seahorses are increasingly regarded as a promising farming object suitable for recirculating aquaculture systems (RASs) due to their high economic value. However, reports on the large-scale farming of seahorses in RASs are rare, and some key parameters, such as stocking densities, are still unclear. In the present study, we employed the lined seahorse (Hippocampus erectus), for which large-scale farming has been achieved, to determine the suitable stocking density for three different-sized juveniles in RASs. The three different-sized juveniles had body heights of 4.0, 7.0, and 9.0 cm, and their test density gradients were 1.0, 0.8, 0.6, and 0.4 inds/L; 0.6, 0.5, 0.4, and 0.3 inds/L; and 0.4, 0.3, 0.2, and 0.1 inds/L, respectively. The juveniles were cultivated for one month, and then their survival, growth, and plasma cortisol and brain serotonin contents (two stress-related indicators) were analyzed. The results show that, regardless of the size of the juveniles, a high density can inhibit growth and trigger stress responses. In addition, for small- (4.0 cm) and medium-sized (7.0 cm) juveniles, a high density can also exacerbate size heterogeneity and cause death. Taking into account the welfare and yield of farmed seahorses, the present study suggests that the suitable stocking densities for 4.0, 7.0, and 9.0 cm juveniles in RASs are 0.6, 0.4, and 0.2 inds/L, respectively.

Seahorse (Hippocampus spp.) is popular in the markets of traditional Chinese medicine, aquarium, and curio. In order to protect wild stocks and still meet the market demand, China attempted the large-scale cultivation of seahorses in the early 21st century and achieved it in the 2010s. However, in recent years, two new issues have gradually emerged in Chinese seahorse cultivation. One is that the juveniles are prone to disease during diet conversion, and the other is that the reproductive performance of broodstocks is significantly reduced. With the aim to provide some measures that can alleviate these issues, in the present study, we used lined seahorse (Hippocampus erectus, a species widely cultured in China) as the experimental subject and Astragalus polysaccharides (APSs) as the immunostimulant to test whether APSs could improve the immune-health status and reproductive performance of seahorses. The measured indices for reproductive performance included ovarian lipid content, assessment time required before mating for paired male and female seahorses, mating success rate, brood size, and newborn body height. The results showed that for juveniles during diet conversion, their body weight, survival rate, plasma immunocytokine contents (interleukin-2, interferon-α, and immunoglobulin M), and alpha diversity indices (Simpson and Pielou’s-e) of the intestinal microbiota were significantly higher than those of the control group after dietary APSs. For broodstocks, compared with the control group, the expression of lipid substances in the ovary was significantly upregulated, the assessment time was significantly shortened, and the body height of their newborns was significantly increased in the APS group. These results demonstrate that APSs could indeed improve the immune-health status and reproductive performance of seahorses, providing guidance for addressing existing issues in seahorse cultivation.

The Chinese bahaba (Bahaba taipingensis), belonging to the Sciaenidae family, is one of the largest croakers with a limited geographical distribution. It is a critically endangered fish species according to the IUCN and a protected animal in China. In this study, the morphological characteristics of Chinese bahaba were observed and analyzed across different developmental stages, namely, the embryonic, larval, juvenile, and young fish stages. The results demonstrated that the mature eggs had a terminal yolk and a single oil globule. The eggs remained floating, and the mean diameters of the fertilized egg and oil globules were 1.14 ± 0.09 mm and 0.35 ± 0.07 mm, respectively. The findings revealed that the embryonic development of Chinese bahaba occurs broadly in seven stages, including the blastogenesis, cleavage, blastocyst, gastrula, neuro embryonic, organ differentiation, and membrane emergence stages, which lasted approximately 27 h and 10 min until hatching under 22.5 ± 0.5 °C. After 70 d, the larvae developed into young fish with a mean total length and body length of 97.75 ± 12.61 and 75.27 ± 13.27 mm, respectively. The digestive organs and the swim bladder began to differentiate, and the swim bladder, bladder duct, intestine, stomach, and mouth gradually formed at 2 d after hatching. Juvenile development occurred via six stages and there were certain differences in the morphological characteristics of Chinese bahaba across the different stages of growth and development. This study provides a theoretical reference for studying the growth, development, and artificial breeding of Chinese bahaba.

This study evaluated the endpoint biochemical responses and associated physiological status of rainbow trout (Oncorhynchus mykiss) of different body sizes during salinity acclimation under varying temperature and salinity conditions. An L₉ (3⁴) orthogonal design was applied using three nominal body-size levels (100, 250, and 500 g), three temperatures (10, 15, and 20 °C), and three salinities (10, 20, and 30‰) over 60 days. Hepatic superoxide dismutase (SOD), alkaline phosphatase (ALP), and acid phosphatase (ACP) activities and plasma malondialdehyde (MDA), urea nitrogen (BUN), ammonia, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were measured. For inferential analysis, the three fish sampled from each tank were averaged to obtain one tank-level value, yielding 18 tank-level observations. Tank-level main-effects analysis showed that body size was significantly associated with ALP, ACP, MDA, BUN, ammonia, ALT, and AST. Temperature was significantly associated with SOD, ACP, MDA, BUN, and AST, whereas salinity was significantly associated with MDA, ALT, and AST. MDA and AST were the only endpoints associated with all three factors. The biochemical responses were pathway-specific rather than uniformly directional across treatment combinations. Because interactions could not be independently estimated in the L₉ design, the identified main effects should be interpreted as orthogonal screening associations. Overall, body-size class was associated with the broadest range of endpoints and should be incorporated into future experimental assessments of rainbow trout within the tested salinity range of 10–30‰.

Using a three-factor orthogonal design, we investigated the transcriptomic and histological responses of triploid rainbow trout (Oncorhynchus mykiss) gills across three salinities (10, 20, and 30 ppt) over 60 days, with temperature and body size as background conditions. Results showed that 20 ppt was associated with extensive transcriptional reprogramming, with 3333 differentially expressed transcripts (DETs), whereas 30 ppt induced only 120 DETs; WGCNA further identified salinity-correlated modules involved in ion transport and ribosome biogenesis. Histological alterations remained within physiological ranges with no salinity-dependent severity gradient, as confirmed by semi-quantitative scoring. These findings demonstrate that triploid rainbow trout gills employ distinct molecular strategies at medium versus high salinity. Within the 10–30 ppt range examined, 20 ppt was the salinity at which transcriptional reprogramming was most active, suggesting that this intermediate salinity warrants further investigation as a potential acclimation stage.