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.

It has been suggested that body colour variation is shaped by both genetic and environmental mechanisms. However, it is not known whether body colour variation among the offspring of a single female occurs in brachyuran crabs. Here, we qualitatively assessed body colour variation in juveniles from a single brood of the varunid crab Gaetice depressus using material reared in the laboratory. This species exhibits body colour variation, and we reared larvae hatched from two females with brownish carapaces and two females with whitish carapaces to the juvenile stage. Brownish females produced juveniles with brownish carapaces, whereas whitish females produced juveniles with either brownish or whitish carapaces. Our experiments suggest the possibility of genotypic colour polymorphism in G. depressus.

Both ovigerous and non-ovigerous females of the cymothoid isopod Anilocra clupei Williams & Bunkley-Williams, 1986 were collected from the body surface of Japanese sardine Sardinops melanostictus (Temminck & Schlegel, 1846) in Aso-kai Lagoon, Kyoto Prefecture, central Japan. The isopod is redescribed herein based on the collected females. Japanese sardine represents a new host record for A. clupei. Based on the previous and present studies, adults of A. clupei have been reported from three species of clupeiform fishes [Japanese sardinella Sardinella zunasi (Bleeker, 1854), round herring Etrumeus micropus (Temminck & Schlegel, 1846), and Japanese sardine], which indicates that these clupeiform fishes are preferred hosts of this parasite and, because of its frequent occurrence records from Japanese sardinella, this fish species is considered to serve as the most important host for the parasite. The isopod occurs in temperate and subtropical waters of Japan, which are possibly affected by two warm currents, the Kuroshio and its branch, the Tsushima Current. An identification key to the three nominal species of the genus Anilocra reported from Japan (A. clupei, A. prionuri Williams & Bunkley-Williams, 1986, and A. harazakii Uyeno & Tosuji, 2023) is also provided.

The commercial value of snow crabs and red snow crabs is low immediately after molting due to low meat quantities and soft shells. As time passes, the meat content and shell hardness increase, making them more valuable. In Japanese market, male snow crabs are arbitrary divided into soft and hard shells. Previous studies also categorized crabs soft-shell and hard-shell arbitrarily and compared the quality between the two groups. A durometer and a penetrometer have been used to determine the shell hardness in the stock management of the snow crab and the red snow crab, but they destroy the crab shells. In the present study, we developed a new non-destructive technique using a portable near-infrared spectrometer to evaluate the dry matter content of pereiopods, which were correlated with the shell hardness. The cheliped was found to be sufficient for measurement in both species, providing a wider range of values and higher precision than the first walking leg. This non-destructive technique would be valuable for assessing both commercial value and the approximate time since the terminal molt of snow crabs and red snow crabs.

A male gnathiid specimen was captured at a depth of 374 m off Cape Muroto, southern Japan. The specimen exhibited small mandibles, extremely large eyes covering most of the lateral cephalon, a slender body, and J- or L-shaped narrow pylopods. These characteristics correspond to those of the monotypic genus Tenerognathia. This specimen, distinct from the type and sole species of Tenerognathia visus, is identified as a new species based on differences in pylopod articulation and shapes of cephalon and maxilliped basis.

An ovigerous female of Argulus matuii Sikama, 1938 was collected from the body surface of a yellowfin seabream Acanthopagrus latus (Houttuyn, 1782) in a cove facing the Bungo Channel off Ehime Prefecture, western Japan. This represents a new host record for A. matuii, and the female collected is herein described. This female, which was fixed and preserved in 70% ethanol, showed a prominent body coloration, i.e., six streaks of yellow fringed with dark brown pigments, on the dorsal surface of the carapace even on 279th day (ca. nine months) after fixation, but the yellow streaks disappeared and the dark brown fringes were fading on 1675th day (ca. four years and seven months) after fixation. Thus, this paper reports on the usefulness of those yellow streaks in identification of A. matuii for a certain period after fixation but also emphasizes the importance of a detailed examination of morphological features in identification of long-term ethanol-preserved argulid specimens. The species is distinguished from the five marine congeners from Japan by its possession of numerous supporting rods in the marginal membranes of the first maxillae.

This study investigated size at sexual maturity of the male sergestid shrimp Lucensosergia lucens ("Sakura-ebi" in Japanese). The shrimps were captured in the inner part of Suruga Bay, Japan in August 2013 using experimental trawls. Carapace length (CL), body length (BL), development of petasma, and presence of spermatophores in the terminal ampoule were documented. Probabilities of maturity as a function of CL were modeled using general linear models with a binomial and logit link function and predicted the CL at which 50% of individuals were mature (CL50). Morphologically mature males had a petasma connected with the pars astringens, and the basal part of the pars media was developed. In physiologically mature males, chambers in terminal ampoules were filled with spermatophores, including spermatozoa and appendages. CL50 (mm) was estimated to be 8.87 (=27.86 mm BL) and 7.84 (=24.65 mm BL) based on the morphological and physiological criteria, respectively. It is believed that most of the age-0 males attain sexual maturity within the first year and mature males are exploited in the autumn fishing season (October–December).

A new species of Hexapinus (Hexapodidae) is described from Hatoma Island, Ryukyu Islands, Japan. Hexapinus patuma, new species, is morphologically close to H. latus Rahayu & Ng, 2014, but can be distinguished by the structures of the carapace and third maxilliped, as well as the degree of setation of ambulatory legs.

An ovigerous female of Nerocila phaiopleura Bleeker, 1857 was collected from the body surface of a Japanese sardine, Sardinops melanostictus (Temminck & Schlegel, 1846) (Clupeidae), caught in Hitachi Port, Ibaraki Prefecture, central Japan. This collection extends the northern distribution limit of N. phaiopleura from Kujukuri, Chiba Prefecture, to Hitachi Port, Ibaraki Prefecture. In Japan, N. phaiopleura has so far been reported from coastal waters of the western North Pacific ranging from southern Kyushu to central Honshu, the East China Sea off Kyushu, and the Seto Inland Sea. While much remains unknown on its distribution in the southern Sea of Japan, N. phaiopleura is found from waters affected by a warm current, the Kuroshio, and its branch, the Tsushima Current. The species has not been found from subtropical waters of the Ryukyu Islands to date. Due to low water temperatures, the species is not likely to occur in subarctic waters affected by a cold current, the Oyashio, and the Kuroshio-Oyashio transition waters off northeastern Japan.

A rare xanthid crab species Cyrtocarcinus truncatus (Rathbun, 1906) is recorded from Ouvéa, Loyalty Islands, New Caledonia, and Ishigaki Island, Ryukyu Islands, Japan. This represents the first record of the species from outside Hawaii. Morphological features and its variations are described in detail.