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Mizuta S.,Fukui Prefectural University | Nishizawa M.,Fukui Prefectural University | Sekiguchi F.,Fukui Prefectural University | Matsuo K.,Okinawa Prefectural Fisheries Research and Extension Center | And 2 more authors.
Fisheries Science | Year: 2013

Enzymatic solubilization of collagen from the skin tissue of diamond squid Thysanoteuthis rhombus, an underutilized resource in Japan, was attempted using an acid protease from the fungus Rhizopus niveus. This novel approach was compared with the conventional method using porcine pepsin. Both proteases were able to solubilize most of the skin collagen (>90 % of the total collagen) by performing the treatment in 0.5 M acetic acid at 4 °C for 72 h and at an enzyme/substrate ratio (w/w) of 1/10. The SDS-PAGE patterns of the solubilized collagen preparations were quite similar to each other, and two types of collagen (major and minor collagens) were purified from each preparation by cation-exchange column chromatography. These collagen types from the porcine pepsin-solubilized collagen showed similar features to those from the Rhizopus acid protease-solubilized collagen. These results suggest that the Rhizopus acid protease, a protease of non-animal origin, is applicable for solubilizing collagen in the skin of diamond squid. © 2013 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 | Year: 2013

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 | Year: 2014

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


Nanami A.,Seikai National Fisheries Research Institute | Ohta I.,Okinawa Prefectural Fisheries Research and Extension Center | Sato T.,Seikai National Fisheries Research Institute
Environmental Biology of Fishes | Year: 2015

The white-streaked grouper (Epinephelus ongus) is an important fisheries target in the region around Okinawa. This species forms spawning aggregations at specific spawning grounds in the last-quarter of the moon in April and/or May. Using a tag-and-release method, we estimated the migration distance and the degree of unified movement of groupers associated with the spawning migration. In total, 1157 E. ongus individuals were tagged and released at their home grounds in the non-spawning period and 350 were tagged at a known spawning ground (Yonara Channel) in the spawning period. For the fish that were released at the home grounds, 23 individuals were recaptured at the spawning ground during in the spawning periods. For the individuals that were released at the spawning ground, six individuals were recaptured outside of the spawning ground. The estimated migration distances from the home ground to the spawning ground ranged from 2.2 to 8.8 km. There was no significant relationship between the fish total length (TL) and migration distance for both males and females. Tagged individuals inhabiting the same home ground were recaptured at different points at the spawning ground separated by a distance of over several hundred meters. Furthermore, tagged individuals that were released at the same point at the spawning ground were recaptured at different home grounds separated by a distance up to several kilometers. These results suggest that unified movements associated with the spawning migration are not high for E. ongus, which is contradict with some previous studies suggesting the coordinated spawning migration of other Epinephelus spp. © 2014, Springer Science+Business Media Dordrecht. 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 | Year: 2014

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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