The swimming crab Portunus trituberculatus is one of the most important economic species in China and its mature ovary often determines its commercial value and production. Although the ovary maturation of crustaceans is generally affected by exogenous nutrition, the specific nutritional needs of ovary maturation of P. trituberculatus are poorly understood. To this end, we collected the P. trituberculatus samples with five ovarian maturation stages and measured their biochemical composition of the ovary, hepatopancreas, and muscle at each ovarian developmental stage. We further analyzed their relation to the ovarian developmental stage of P. trituberculatus by principal components analysis (PCA). We found the levels of branched-chain amino acids, long-chain polyunsaturated fatty acids (LC-PUFA), and monounsaturated fatty acids (MUFAs) in the ovary and hepatopancreas increased during the ovary maturation process, and also passively correlated with ovarian developmental stage, which highlights the necessity of these specific nutrients for oogenesis and for improving the nutrient quality of crabs. In addition, we found an increasing tendency of carotenoid content and phosphatidylcholine in phospholipid in the ovary from the pre-developmental stage to the proliferative stage, but not in the hepatopancreas and muscle, which highlights the possible involvement of carotenoids during the rapid oocyte development process. Our study may provide valuable information for developing a suitable broodstock diet that promotes the ovarian maturation of adult P. trituberculatus and ensures high-quality larval production.

Water temperature is one of the most important factors greatly affecting the aquaculture of sea urchins. However, no information is available on how to improve commercial traits of sea urchins reared at high water temperature. Here, we investigated the effects of water temperature and feeding regime on food consumption, growth, gonad production, gametogenesis and gonad quality of the sea urchin Strongylocentrotus intermedius. We found that high water temperature (22°C) significantly decreased dried food consumption and gonad production of S. intermedius, but not the somatic growth. The feeding regime of formulated feed and kelp has direct application potential in S. intermedius aquaculture, especially at field temperature. Feeding kelp alone is not effective in supporting growth and gonad production for S. intermedius cultured at high water temperature. This finding greatly challenges the current commonly used feeding regime (feeding macroalgae only) for S. intermedius cultured at high water temperature. Based on the current results, we suggest the feeding regimes of formulated feed and kelp or formulated feed alone for S. intermedius aquaculture at high water temperature. The present study provides new information for aquaculture of S. intermedius at high temperature and for production out of season.

Ocean warming has facilitated the range expansion of commercially important sea urchin species to higher latitudes. Heliocidaris crassispina was recorded to extend northward to Toga Bay along the Oga Peninsula, Japan following an increase in seawater temperatures, and replacement of local sea urchin species Mesocentrotus nudus. In order to identify evidence of adaptation occurring in response to a range extension of H. crassispina to the newly extended environments, we randomly collected 106 H. crassispina in August 2014 in Toga Bay, determined the growth and age composition and examined gonad traits (size, color and development). To confirm the gonad development, 30 H. crassispina with > 30 mm diameter were collected in July, August and September 2017. We found slower growth in the extended range than the central range. More delayed gonad development of males than those of females and a large variety of developmental stages in the acini of testis indicated that the spawning of both sexes of the sea urchins were asynchronous. In terms of gonad color, L* (lightness) values increased with increasing GI, while b* (yellowness) values decreased with increasing age. The population consisted of seven year-classes from 2006 to 2012, suggesting persistent juvenile recruitment. Long-term water temperature data indicated that the range extension of H. crassispina was due to ocean warming, in particular during the summer spawning season.

In the field, both covering materials and shelters are commonly available to sea urchins. The behavioural decision between covering and sheltering thus obviously exists. However, no information is available on the preference between the two natural behaviours. Two conditions were designed with covering and sheltering materials to comparatively describe the diel trade-off between covering and sheltering behaviours in male and female Strongylocentrotus intermedius. In the present study S. intermedius had an obvious diel trade-off between covering and sheltering behaviours, preferring covering over sheltering when both behaviours were possible. Sex did not significantly affect the trade-off between the two behaviours, no matter whether covering materials were inside or outside the shelters. The rhythm of covering behaviour was not well correlated with intensity of light in the trade-off with sheltering behaviour. The present study provides new insights into behavioural ecology of sea urchins.

Biofloc technology (BFT) is an advanced aquaculture method that uses microbial communities to enhance water quality and support aquatic species cultivation. Our research aims to delve into the pivotal role of aeration intensity within BFT systems, revealing its influence on microbial community structures, water quality, and nutrient cycling for L. vannamei culture. Three aeration levels were set with intensities of V75 (75 L/min), V35 (35 L/min), and V10 (10 L/min). The results showed that the lowest aeration intensity (V10) resulted in larger floc sizes and a reduction in the 2D-fractal dimensions, indicating a decreased overall structural complexity of the bioflocs. In addition, water quality parameters, including total ammonia nitrogen and nitrite, remained low across all treatments, highlighting the water-purifying capacity of biofloc. While protein and lipid contents in biofloc did not differ significantly among treatments, docosahexaenoic acid (DHA) levels were highest in the V75 treatment, suggesting that higher aeration promotes the accumulation of essential fatty acids. RDA analysis revealed that microorganisms like Ruegeria sp. and Sulfitobacter mediterraneus negatively correlated with ammonia and nitrite levels, suggesting their key role in converting ammonia to nitrite and nitrate in marine nitrogen cycles. The functional annotation of metagenomes across different aeration levels showed the similarly active roles of microorganisms in nitrogen metabolism and protein synthesis. In conclusion, while variations in aeration intensity affect floc size and the accumulation of essential fatty acids in biofloc, they do not significantly impact overall water quality or core microbial functions in L. vannamei aquaculture. Future research should focus on the effects of aeration strategies on microbial community dynamics and the integration of these data with performance metrics in L. vannamei. These insights can help optimize biofloc cultivation and enhance environmental sustainability in the aquaculture industry.

Ocean warming has facilitated the extension of Heliocidaris crassispina to Oga Peninsula, Japan, where the native species Mesocentrotus nudus has disappeared. To verify the temperature impacts on the physiology and behaviour of the two species, we reared small sea urchins at the increasing–decreasing temperature rate of 2.5 °C·week⁻¹. The righting response, lantern reflex, gonad and gut carbon (C) and nitrogen (N) contents, and feeding rate were investigated. The high and low temperature limits of H. crassispina were 33.3 and 3.9 °C, respectively, which were higher than those of M. nudus. The optimal temperature ranges for behaviour and feeding in H. crassispina were 10.3–31.0 and 10.3–33.4 °C, respectively, which were higher than those in M. nudus. Feeding rates decreased significantly in both species when the temperature approached the high or low temperature limit, but the gut C and N contents of were not greatly affected. At 26–31 °C, the feeding rate significantly decreased in M. nudus but not in H. crassispina, which may explain the replacement of M. nudus by H. crassispina in the Oga Peninsula.