Improvement of ovulation induction by additive injection of 17,20β‐Dihydroxy‐4‐pregnen‐3‐one after human chorionic gonadotropin administration in a pelagic egg spawning marine teleost,nibe croaker Nibea mitsukurii (Jordan & Snyder)

This study aimed to develop the consistent ovulation induction method in a pelagic egg spawning marine teleost, nibe croaker Nibea mitsukurii. Attempts to induce oocyte maturation and ovulation in nibe croaker using human chorionic gonadotropin (hCG; 0.5 IU g^?1) resulted in the normal progression of oocyte maturation and hydration, but a failure to induce ovulation in many individuals. This ovulation disorder was similarly observed even when the dose of hCG was increased 10 times (5 IU g^?1) or decreased to one tenth (0.05 IU g^?1), indicating that it cannot be completely overcome solely by hCG administration. However, this ovulation disorder could be completely overcome by subsequent administration of 17,20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) at the appropriate dose (0.5 μg g^?1) and time (20 h after hCG administration). An increase in the number of individuals that ovulated due to DHP administration led to an increase in individuals producing larvae, resulting in an approximately threefold increase in the estimated number of larvae produced compared with the group of fish administered hCG alone. Thus, this ovulation induction method using DHP administration after hCG was demonstrated to overcome the ovulation disorder in nibe croaker and could be applicable to commercially important species with similar ovulation problems.     

Factors Influencing Early Survival and Growth of Laboratory‐reared Pacific Bluefin Tuna,Thunnus orientalis,Larvae

The collection of fertilized eggs for mass culture of Pacific bluefin tuna (PBT) relies on the spontaneous spawning of broodstock in captivity, and the spawning season of the broodstock is generally from mid‐May to September. The diameter of fertilized eggs from the broodstock decreases during the spawning season. To investigate the influence of three potential factors, the egg diameter (larger or smaller), the rearing water temperature (25 or 28 C), and the aeration rate during the night (strong or weak), on early survival and on growth of PBT larvae, replicate trials were conducted to assess these three factors until 7 d after hatching (d.a.h.). At 7 d.a.h., survival rates of larvae reared with strong nighttime aeration were found by a three‐way ANOVA to be significantly higher than for larvae reared with weak aeration. Furthermore, growth rates of PBT larvae hatched from larger eggs were significantly faster than those from smaller eggs. However, a significant difference in the survival rate was not detected for the factors, egg diameter and rearing water temperature. The results indicate that rearing with strong nighttime aeration significantly improved the early survival of PBT larvae and the egg diameter (a proxy for egg quality) and influenced growth.     

Replacement of dietary fish oil with olive oil in young yellowtail <Emphasis Type="Italic">Seriola quingqueradiata</Emphasis>: effects on growth,muscular fatty acid composition and prevention of dark muscle discoloration during refrigerated storage

Dietary fish oil (FO) was replaced by olive oil (OO) in young yellowtail Seriola quinqueradiata to investigate its effects on growth, muscular fatty acid composition and prevention of color deterioration of dark muscle during storage. Yellowtail were fed one of four diets, where FO (80 g/kg diet) was replaced by OO (0, 25, 50 and 100%) for 40 days. No significant difference in growth was seen among the diet groups. In addition, these experimental diets did not affect the proximate compositions of the dorsal muscle, ventral muscle and the liver in these fish. Serum total protein, glucose and total cholesterol levels did not show significant differences; however, serum triglyceride levels were significantly higher in fish fed 50 and 100% OO diets. Fatty acid composition of ventral muscle reflected the composition of the respective diets. Dark muscle discoloration was reduced in fish fed OO diets after 12 to 18 h during storage at 4°C. Furthermore, the redness value of fresh dark muscle increased depending on the extent of FO replacement. These results indicate that the partial or total dietary replacement of FO with OO prevents discoloration of dark muscle without affecting the growth of young yellowtail after 40 days of feeding.     

Evaluation from otolith Sr stable isotope ratios of possible juvenile growth areas of Japanese eels collected from the West Mariana Ridge spawning area

Fisheries Science - The widely distributed East Asian Japanese eel Anguilla japonica constitutes a single genetically homogeneous population with a single spawning area near the West Mariana Ridge....