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The head is a major by-product (17.1% of body weight) of sturgeon aquaculture farming and remains unutilized. In this study, the sturgeon head was separated into the skull cartilage and mixed tissue: skin, scales, fins, muscles, bones, gills, and small cartilage pieces. Type A and B gelatins were extracted from the mixed tissue. The type B yield was higher, at 5.8% gelatin dry weight per tissue wet weight. The relative gelatin content in the sample weight, estimated from the sample's hydroxyproline content relative to that of the purified collagen, was higher in type A (60.3%) than in type B (39.7%). Type A gelatin showed higher intensities of the alpha- and beta-bands of gelatin in SDS-PAGE, indicating that gelatin purity was higher in type A. The breaking force-strain curve showed a larger breaking force and lower breaking strain in type A (2.0 N, 12.1%), indicating that this gelatin is stronger than type B (0.7 N, 15.8%). Type B gelatin featured higher emulsion activity and stability and higher foam expansion and stability. In conclusion, type A and B gelatins with distinct proximate composition and functional properties were successfully extracted from sturgeon heads, which could act as a promising source of gelatins for industrial applications.

To develop a new method for extracting gelatin from the sturgeon head, the conditions for pretreatment and extraction were optimized. Treatment at 65 degrees C (3-3.5 h) was enough to separate the head into mixed tissues (skin, scales, pectoral fins, muscle, bones, gills, and small cartilage pieces), skull cartilage, and liquid. From the intensities of alpha-, beta- and gamma-bands and yields, the optimized pretreatment conditions for type A and type B gelatin were 0.05 M HCl (1 h) and 0.1 M NaOH (1 h), respectively. The best extraction conditions were: (1) for type A gelatin: with distilled water (DW) (w/v 1:5) at 35 degrees C, pH 7 when stirring at 200 rpm for 3 h, and (2) for type B gelatin: with DW (w/v 1:5) at 50 degrees C, pH 8 when stirring at 200 rpm for 1 h. After the decalcification of extracted residues with 0.05 M HCl for 3 h, re-extraction of gelatin was possible. Under the best extraction conditions, yields of type A and B gelatins were 5.01 and 7.25% (dry gelatin weight/wet sample weight), respectively. Thus, it is possible to extract an industrial amount of gelatin from sturgeon heads, making them valuable by-products.

We examined the reproductive cycle and transcription-level changes of the major yolk protein (MYP) in gonads of both sexes during the different reproductive stages of wild northern sea urchin, Mesocentrotus nudus, collected in two areas of southern Hokkaido, Japan. Histological evaluation revealed mature gonads in both April and August, suggesting two annual spawning seasons at Otoshibe, whereas one annual spawning season was observed in autumn (September) at Usujiri. The transcription levels of MYP, which is synthesized and stored in the gonads, increased from stage 1 (recovering) to stage 2 (growth) and thereafter decreased, in both female and male sea urchins. The current results indicate that two annual spawning seasons may occur in wild populations of the northern sea urchin in southern Hokkaido.