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Ebisawa A.,Okinawa Prefectural Fisheries and Ocean Research Center | Kanashiro K.,Okinawa Prefectural Fisheries and Ocean Research Center | Kanashiro K.,Okinawa Prefectural Sea Farming Center | Kiyan T.,Okinawa Prefectural Fisheries and Ocean Research Center
Fisheries Science

The growth, sex ratio with age, and age at sexual maturation were determined based on sectioned otoliths in 257 specimens of the blackspot tuskfish Choerodon schoenleinii collected in waters off Ryukyu Island. Opaque rings observed by reflected light in the sectioned otoliths were found to form once a year from January to July. The three growth parameters of the von Bertalanffy growth equation were L∞ = 68. 1 (cm), k = 0.263, and t0 = -0. 023 (year). The age at which the sex ratio reached 50% by sexual transition was about 6.15 years, and the age at which 50% of females were sexually mature was approximately 2 years. The oldest specimen among the samples was 17 years old. © 2010 The Japanese Society of Fisheries Science. Source

China M.,Forestry and Fisheries Promotion Center | Nakamura H.,Okinawa Prefectural Sea Farming Center | Hamakawa K.,Okinawa Prefectural Fisheries Research and Extension Center | Tamaki E.,Okinawa Prefectural Sea Farming Center | And 4 more authors.
Fish Pathology

In 2008, the myxosporean emaciation disease was found in cultured Malabar grouper Epinephelus malabaricus in a fish farm in Okinawa Prefecture, Japan. The disease occurred in winter when water temperature ranged from 21 to 26°C, and the cumulative mortality reached 20-50% among culture tanks. In affected fish, cranial bones were externally apparent due to severe emaciation. The intestinal wall was very thin and the liver exhibited conspicuous green color. Morphological and molecular analyses demonstrated that the causative myxosporean was Enteromyxum leei. Histopathological examinations revealed that the epithelia of the intestine and bile duct of diseased fish were heavily infected with E. leei. The common bile duct was often obstructed by severe inflammation with degenerated tissues and bacteria, suggesting that the abnormal color of the liver was caused by cholestasis. Some diseased fish recovered in a laboratory when water temperature increased naturally to 27-30°C in summer months, and the parasite was not detected in those fish. Experimental transmission of E. leei to naive Malabar grouper was successfully achieved by cohabitation with infected grouper or by feeding with the feces of infected fish. This is a new host and locality record for E. leei. Source

Murata R.,University of Ryukyus | Kobayashi Y.,University of Ryukyus | Kobayashi Y.,Okayama University | Karimata H.,Okinawa Prefectural Sea Farming Center | And 3 more authors.
Biology of Reproduction

To clarify the cause of sex change recovery after the withdrawal of androgen treatment, immature female Malabar grouper were fed a diet containing 17alpha-methyltestosterone (MT) at 50 μg/g for 7 mo and then a normal diet for 6 mo. The MT brought about precocious sex change from immature ovaries to mature testes with active spermatogenesis, including the development of spermatozoa, and sex change reversed soon after MT treatment withdrawal. This result indicates that precocious sex change in immature Malabar grouper with oral MT treatment is impermanent. The expression of three steroidogenic enzymes (Cyp11a, Cyp19a1a, and Cyp11b) in the gonads of the Malabar grouper were analyzed immunohistochemically at the end of the 7-mo treatment. No apparent differences were seen in the expression pattern of these enzymes between the mature testes of MT-treated fish and the immature ovaries of control fish. In addition, serum estradiol-17beta and 11-ketotestosterone levels in treated fish were the same as those in control fish. These results indicate that in the case of immature Malabar grouper MT might have little effect on endogenous steroidogenesis during precocious sex change even though it induced active spermatogenesis in the gonads of treated fish. From these results, we also concluded that MT might have little effect on the steroidogenic endocrine pathway, and this is one cause of sex change recovery after treatment withdrawal. © 2014 by the Society for the Study of Reproduction, Inc. Source

Kurihara T.,Seikai National Fisheries Research Institute | Yamada H.,Seikai National Fisheries Research Institute | Inoue K.,Okinawa Prefectural Fisheries and Ocean Research Center | Iwai K.,Okinawa Prefectural Sea Farming Center | Hatta M.,Ochanomizu University

To survive the juvenile stage, giant clam juveniles need to establish a symbiotic relationship with the microalgae Symbiodinium occurring in the environment. The percentage of giant clam juveniles succeeding in symbiosis establishment ("symbiosis rate") is often low, which is problematic for seed producers. We investigated how and why symbiosis rates vary, depending on whether giant clam seeds are continuously reared in UV treated or non treated seawater. Results repeatedly demonstrated that symbiosis rates were lower for UV treated seawater than for non treated seawater. Symbiosis rates were also lower for autoclaved seawater and 0.2-μm filtered seawater than for non treated seawater. The decreased symbiosis rates in various sterilized seawater suggest the possibility that some factors helping symbiosis establishment in natural seawater are weakened owing to sterilization. The possible factors include vitality of giant clam seeds, since additional experiments revealed that survival rates of seeds reared alone without Symbiodinium were lower in sterilized seawater than in non treated seawater. In conclusion, UV treatment of seawater was found to lead to decreased symbiosis rates, which is due possibly to some adverse effects common to the various sterilization techniques and relates to the vitality of the giant clam seeds. © 2013 Kurihara et al. Source

China M.,Forestry and Fisheries Promotion Center | Nakamura H.,Okinawa Prefectural Sea Farming Center | Hamakawa K.,Okinawa Prefectural Fisheries Research and Extension Center | Tamaki E.,Okinawa Prefectural Sea Farming Center | And 2 more authors.
Fish Pathology

The effect of elevated water temperature on the myxosporean emaciation disease caused by Enteromyxum leei was tested in experimentally infected anemonefish Amphiprion ocellaris and naturally infected Malabar grouper Epinephelus malabaricus. Anemonefish reared at 30°C following infection had significantly lower parasite prevalence compared to fish reared at 23°C. After infection in anemonefish held at 23°C for 20 days, elevation of water temperature to 30°C reduced the prevalence. Holding infected Malabar grouper at 30°C resulted in a clearing of E. leei within 6 days. Histopathological observations showed that E. leei was eliminated following exfoliation of the intestinal epithelial cells. Although further replication of the study would be required, these results suggested that high water temperature treatment had a preventive and therapeutic effect on myxosporean emaciation disease. © 2014 The Japanese Society of Fish Pathology. Source

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