This study investigated effects of dietary sulfur amino acid-related compounds on the content of these compounds in the hepatopancreas, the gene expression of taurine-synthetic enzymes, somatostatin, and growth hormone, and the growth and morphology of the common carp, Cyprinus carpio. Juvenile common carp were fed one of nine diets: a basal diet supplemented without sulfur compound (control); a basal diet supplemented with 1.0% or 1.5% cysteamine hydrochloride (CSH); 1.5% or 3.0% cysteine; 1.0% or 1.5% methionine; and 0.5% or 1.0% taurine for 30 d. The 1.0% and 1.5% CSH supplementation caused growth retardation and deformities in the fish. All treatments increased carcass taurine levels (18.5-86.9 g/kg). The highest whole body taurine content was observed in fish fed the 1.5% CSH-supplemented diet. Cysteine dioxygenase was downregulated by cysteine and 0.5% taurine but upregulated by 1.5% CSH. Cysteine sulfinic acid decarboxylase was downregulated by cysteine, methionine, and CSH. Cysteamine dioxygenase was downregulated by methionine, cysteine, and 0.5% taurine but upregulated by CSH. Somatostatin 14 was upregulated by CSH. Insulin-like growth factor-1 was upregulated by 1% taurine and cysteine but downregulated by 1.5% CSH. The present study suggests that the cysteamine pathway is mainly responsible for taurine synthesis in common carp.

The feeding habits, age, growth and reproductive biology of C. nasus in the Rokkaku River estuary, innermost area of Ariake Bay were determined from specimens collected from May 2012 to May 2014. Stomach contents analyses showed that their prey components were crustaceans, polychaeta and fishes. Examination of the outer margins of the sectioned otolith showed that the translucent zone was formed once a year, and can be used as an annulus. Growth of fish, expressed by the von Bertalanffy growth equation, was L_t = 398 (1 - exp [- 0.27 {t + 0.93}]) for males and L_t = 437 (1 - exp [- 0.33 {t + 0.48}]) for females, where L_t is body length (mm) and t is age in years. The observed maximum ages were 4 years for males and females, respectively. Reproductive biology was studied on the basis of gonadosomatic indices and histological sections of gonads. The spawning season lasted from April to August, peaking in June and July. Body length at 50% sexual maturity was 135 mm for males and 196 mm for females. The biological minimum size was 123 mm for males and 156 mm for females in body length.

The Pacific bluefin tuna Thunnus orientalis (PBT) is an important food resource species in aquaculture. To evaluate somatic growth, it is important to understand the nutrition and organ development of larval and juvenile fish. In the present study, we examined nutritional composition and organ-specific enzyme activity of laboratory-reared PBT during early development. Experimental fish were reared at the Kindai University Fish Nursery Centers at Wakayama, Japan. Sampling was carried out from 0-32 days after hatching (DAH). At 15 DAH, the standard length and wet body weight rapidly increased, reflecting the completion of morphological change from the flexion to the postflexion phase. Although the moisture content (%) gradually decreased, the protein contents (%) increased during development. Fat, glycogen, and ash contents did not increase as much as protein content, suggesting that the decremental moisture content was mainly replaced with protein content. In addition, the activity of bone-specific alkaline phosphatase, a bone formation marker, was higher than that of tartrate-resistant acid phosphatase, a bone resorption marker. We assume that bone mineralization is promoted in the early life stages of PBT through the activation of bone formation. These data will contribute to the development of suitable rearing technologies for the mass production of PBT fingerlings.

For future sustainable aquaculture practices, utilization of a low fish meal diet in a Yamanashi strain of rainbow trout was compared with another strain. In addition, efficacy of selective breeding for the low fishmeal diet was preliminarily examined in the Yamanashi strain. A 50% fishmeal diet (FMD) and a soybean and corn gluten meal-based 5% fishmeal diet (LFMD) were fed to apparent satiation to the juveniles of Yamanashi control strain (YC), Shiga Samegai strain (SS) and Yamanashi strain selectively-bred for one generation with LFMD (YS). Growth and feed utilization for the respective diets were similar between YC and SS strains. Among fish fed LFMD, apparent dietary crude protein and fat digestibility coefficients were higher in YC than those in SS. Selectively-bred YS showed superior growth and feed efficiency to YC for the respective diets due largely to increased feed intake. However, limited improvements in the physiological conditions were observed in YS fed LFMD. An additional trial under restricted feeding of LFMD revealed that growth and feed efficiency ratio of YS were superior to YC. These results suggest that selective breeding of Yamanashi strain rainbow trout with a low fishmeal diet is effective for improvement of this diet utilization.

Information on effects of different enrichment on different morphotypes within the Brachionus plicatilis sp. complex is limited. This study investigated the effects of different enrichment diets on population growth, fatty acid content and protein content of L and SS types B. plicatilis sp. complex. Three commercial rotifer enrichment formulations were tested: docosahexaenoic acid (DHA) enriched Chlorella vulgaris, frozen Nannochloropsis oculata, salmon roe emulsion oil, against a control diet of normal C. vulgaris. DHA-enriched C. vulgaris and Frozen N. oculata had significantly higher population growth, fatty acid composition and soluble protein in both morphotypes. However, population growth under salmon roe emulsion treatment was affected negatively despite having high essential fatty acid content in both morphotypes. Variations in fatty acid assimilation in non-polar and polar lipids between morphotypes were observed highlighting enrichment effects and possible dissimilar biochemical roles of these compounds in tissue metabolism in each morphotype. Significantly higher levels of soluble protein were detected in DHA-enriched C. vulgaris and control treatment. SS-type had significantly higher soluble protein content except under the frozen N. oculata treatment. Culture method, enrichment type and dosage are important considerations as different rotifer morphotypes respond differently to different enrichment.

Rearing experiments under controlled environmental conditions further our understanding of the population dynamics of walleye pollock Gadus chalcogrammus by supplementing the biological information collected in field surveys. However, walleye pollock rearing techniques, from eggs to juveniles, still require improvement. In the present study, we investigated the effects of taurine enrichment of early live food on the survival and growth of walleye pollock larvae. Larvae were fed with unenriched (control) and taurine-enriched rotifers (taurine supplementation: 400 mg/ml) from the first feeding until 22 or 23 days post hatching (DPH) in Experiment 1, and with unenriched (control) and taurine-enriched rotifers and Artemia nauplii (taurine supplementation: 800 mg/ml) until 55 DPH in Experiment 2. In both experiments, the survival and growth of the larvae reared on taurine-enriched food were improved, when compared with the control larvae. The growth rates and taurine content of the supplemented larvae were comparable to those of wild-caught larvae. Our findings suggested that taurine enrichment of early live food effectively improved the rearing performance of walleye pollock larvae. Such improvements may facilitate the supply of experimental fish for future laboratory studies on the biological characteristics of the larval and juvenile stages of this species.

We investigated the growth, survival, and reproduction performance of rainbow trout (Oncorhynchus mykiss) fed 5% fish meal diets (ELFM group) from the juvenile stage to the 3-year-old mature stage. Fish in the control group were fed approximately 50% fish meal diets (FM group). The growth of the ELFM group was significantly inferior to the FM group. However, survival rates and egg quality parameters were not significantly different between groups. Thus, a 5% fish meal diet could be used in almost all stages of rainbow trout farming and reproduction for selective breeding.

Seeds of the iwagaki oyster, Crassostrea nippona, are generally produced using artificial cultivation for aquaculture. Therefore, a sufficient number of seeds should become attached to ensure product quality. In this study, we investigated the effects of larval density and the number of spat collectors in each tank on the attachment rate of seeds on scallop shells. On average, the proportion of scallop shells with >20 seeds attached was 80% with a larval density of 0.5/ml and 86% when the aquarium contained >1,000 larvae per scallop shell. These finding indicate that iwagaki oyster larvae should be reared at a density of 0.5/ml in a 1000 l tank contained 500 scallops during the settlement period to stably obtain a sufficient number of seeds.

Japanese common sea cucumber Apostichopus japonicus is one of the most important fisheries species of the world, while the natural resources are declining recently. We examined the retention rate of single spaghetti tags applied to A. japonicus to use future mark-recapture studies for estimating their stocks and/or their ethology. Eight of 10 individuals retained the tags for 76 days under 12°C. The retention rate is high compared to the other studies using spaghetti tags on Aspidochirotida, and that is practical levels to utilize for ecological and/or conservation studies in the active and reproductive season of A. japonicus.

In order to investigate the relationship between biliary bile acid levels and taurine biosynthesis in fish, bluegill Lepomis macrochirus was fed on the diets containing different levels of cholestyramine and 0.4% of taurine or glycine-conjugated bile acid for 30 and 22 days. At the end of each experiment, activities of hepatic enzyme involved in amino acid metabolism including taurine biosynthesis and muscular taurine and biliary bile acid levels were determined.
Feeding of cholestyramine significantly reduced gallbladder bile acid content at a dose dependent manner, but cysteinesulfinate decarboxylase activity, a key enzyme of taurine biosynthesis, remained unchanged. Hepatic alanine aminotransferase decreased inversely in proportion to the cholestyramine intake.
Supplementation of conjugated bile acids trended to result in lower body weight, probably due to their poor palatability, but each bile acid was found as a predominant component in gallbladder bile acid of the fish. However, cysteinesulfinate decarboxylase activity was not affected by the bile acid ingestions in this trial.
Our present data indicate that change of biliary conjugated bile acid level does not influence taurine biosynthesis in bluegill. It seems that taurine and its conjugated bile acids firstly play an excretion form in cholesterol and sulfur amino acid in this fish.

Cooperation of recreational anglers is indispensable to prevent ayu cold-water disease, but the present status for their understanding has been insufficiently evaluated. We here report a questionnaire survey on the anglersʼ awareness in a local ayu-fishing competition of Mie Prefecture. A total of 598 responses from 2015 to 2018 were considered of 393 (65.7%) responses with taking preventative measures and 135 (22.6%) responses taking no measure. Among the 150 repeaters who were able to pursue their answers, 22 persons improved their awareness whereas 20 persons stopped taking measures or provided unclear answers. These suggest an incomplete status still requiring further enlightenment.