This study examined the growth dynamics, enzyme activity, and histological development of Neocaridina denticulata juveniles in controlled aquaculture conditions. Individual body weight and length variations were attributed to microenvironmental factors and social interactions. Transparent tank systems and localized environmental niches likely influenced resource competition and growth. Despite suboptimal temperatures (16.9–19.1°C, below the ideal 22–26°C), juvenile development remained unaffected, indicating broader temperature tolerance than previously recognized. Histological analysis revealed that the digestive structures of juveniles (15–60 days after hatching, DAH) and adults (>75 DAH) were remarkably similar, supporting isometric growth and highlighting a robust digestive system across life stages. Enzyme activity analysis, conducted with minimal sample sizes (10 individuals), effectively detected growth-related trends. Amylase and lipase activities showed dynamic patterns shaped by developmental programs and environmental factors, while protease activity increased steadily, reflecting the nutritional demands of growing juveniles. Adults exhibited significantly higher lipase activity than shrimplets, likely due to reproductive and metabolic requirements. This study underscores the efficiency of direct development in N. denticulata, providing valuable insights into its physiological and behavioral adaptations. The findings offer significant implications for aquaculture practices, particularly in enhancing shrimplet growth and survival under controlled environmental conditions.

Accelerated aquaculture production has driven demand for novel ingredients in aquaculture feeds. Potential alternatives include single cell organisms, transgenic crops and terrestrial arthropods for example the black soldier fly, Hermetia illucens. Underutilised aquatic taxa, such as amphipods, possess a wide range of unsaturated and polyunsaturated fatty acids valued by the aquaculture feed industry. However, information regarding composition of semi-terrestrial talitrid amphipods remains at an exploratory stage. For instance, Talitrus saltator is a common European sandhopper currently lacking published, comprehensive body composition and lipid analysis data. In this study, monthly sampling of T. saltator (July–September) showed a distinct increase in body size, energy value, protein content and storage lipids (triacylglycerols) likely due to increased foraging potential during the warmer and more productive summer period. Toward the end of the summer, sandhopper proximate composition was comparable to other arthropod meals (Krill, Euphausia superba, amphipod Gammarus sp., and H. illucens). Whilst T. saltator fatty acid composition was biased toward monounsaturated fatty acids (ranging from 44.1–57%), samples also contained a range of polyunsaturated fatty acids, including valuable omega 3 long chain fatty acids. However, there remains scant information on T. saltator harvesting or culture potential, likely essential to produce biomass of sufficient quantity or composition for commercial use.

Salmincola californiensis, an ectoparasitic copepod, infects salmonid fishes’ branchial cavities and fins, mainly of Oncorhynchus species. While this species is widely distributed along the Northern Pacific Ocean rim, only three populations have been documented in Japan, and these records are primarily from highly fragmented local areas at high altitudes or latitudes. Here, we report S. californiensis parasitizing masu salmon Oncorhynchus masou masou captured in upstream reaches of the Naka River, Tochigi Prefecture, central Honshu. This is the fourth locality record in Japan and for the first time in 40 years. Copepods were identified as S. californiensis based on partial 28S rDNA sequences. Infection levels were relatively high (Prevalence 66.7%, mean intensity 5.0), and some copepod individuals had egg sacs, suggesting that this population is naturally sustained. Given their fragmented distributional records in high-altitude areas and considering that Japan represents the southernmost margin of their distributional range, these populations are assumed to be glacial relics.