The maximum absorption wavelength (λ_max) of the photosensitive pigment retinochrome present in the retina of squids is approximately 10 nm longer than that of rhodopsin, and it is known to be abundant in deep-sea species. When comparing the λ_max difference between the two pigments among three species of Sepioteuthis spp., the difference in S. sp. 2, which is common in Honshu, was 17 nm, and less than 2 nm for southern species of S. sp. 1 and S. sp. 3. Retinochrome gene expression intensity was higher in S. sp. 2, which is common in inland bays, than in S. sp. 1, which occurs in deep waters. The habitat of S. sp. 2 has greater fluctuations in turbidity than that of the other two species, and it is presumed that S. sp. 2 adapts its visibility to the complex light environment by actively utilizing two photopigments with different λ_max.

　The three species of Sepioteuthis spp. inhabiting the waters off the coast of Japan frequently appear in different areas and depths. We isolated the rhodopsin gene, and also compared the wavelength sensitivity of these squid species by measuring the maximum absorption wavelength (λ_max). The full length of the rhodopsin gene for all three species was 1356 bp and was translated into 452 amino acid residues. The λ_max value was 496, 492, and 489 nm for S. sp. 1, S. sp. 2, and S. sp. 3, respectively, with S. sp. 1 from the deepest habitat showing the longest wavelength, opposite to the typical depth-related trend. In general, the λ_max value of aquatic animals is shorter for those inhabiting deeper waters. It is suggested that the difference of about 100 m between the three Sepioteuthis spp. may not be reflected in the rhodopsin λ_max.

　Since spring 2022, the catch of the venerid clam Paphia euglypta in Harima-nada, Hyogo Prefecture, has increased rapidly, and the species is now widely sold in the market. To promote its utilization, this study investigated the catch trends and characteristics of the raw materials. Fishing with small trawl nets in sandy-mud areas at depths of 20–30 m has expanded since around 2019, with approximately 8 tons landed at the Ichinomiya Fisheries Cooperative in 2022. Shell length showed a modal range of 69.0–75.0 mm throughout the fishing season, and both the condition factor and protein, carbohydrate and lipid contents increased from January to May. Notably, the edible portion of Paphia euglypta contains a high concentration of selenium (Se, 120 µg/100 g), suggesting its potential as a functional marine food material.

　Red-fleshed fish meat, including yellowtail Seriola quinqueradiata and tuna, will turn brown, losing its freshness and commercial value. Browning reflects the met formation of myoglobin (Mb), and the met ratio, an index of browning, is expressed as the ratio of met Mb to total Mb. Generally, the met ratio is determined by absorptions at two to four wavelengths. In the present study, to determine the met ratio of yellowtail, the absorption spectra from 500 to 650 nm were used. The spectra of the untreated extract were well reconstituted using those of oxy, deoxy, and met Mbs, validating the method of using the spectra. The present method could be applied to other fish or mammalian Mbs to determine the met Mb ratio.