Okinawa Prefectural Fisheries Research and Extension Center

Okinawa, Japan

Okinawa Prefectural Fisheries Research and Extension Center

Okinawa, Japan
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Inoue K.,Okinawa Prefectural Fisheries Research and Extension Center | Terashima Y.,Nagasaki University | Shirakihara M.,Toho University | Shirakihara K.,University of Tokyo
Aquatic Mammals | Year: 2017

Habitat use by Indo-Pacific bottlenose dolphins (Tursiops aduncus) with a maximum group size > 100 individuals in the northern coastal waters of Amakusa-Shimoshima Island, western Kyushu, Japan, was examined for 51 d between October 1996 and December 1997. Systematic behavioral sampling and theodolite tracking techniques were used to collect data. The core habitat area (CHA), defined as the 50% kernel density estimate, was located in the northern coastal area near Tsuji Island. Occurrences of dolphin groups in the CHA were higher during ebb and low tides. A group behavior that corresponded to resting was seen around the CHA, while both traveling and feeding were seen in a wider area outside of the CHA. Dolphin groups were found in the eastern area of the CHA during morning hours, and the groups spent more time in the CHA in the afternoon hours. Unidirectional movements, mainly toward western offshore waters, occurred after 1600 h. Numerous dolphin-watching boats are attracted to the CHA. Managing policies and enforcement are required for the local dolphin-watching industry.

Ikeda S.,Hiroshima University | Yamashita H.,Seikai National Fisheries Research Institute | Kondo S.-N.,Okinawa Prefectural Fisheries Research and Extension Center | Inoue K.,Okinawa Prefectural Fisheries Research and Extension Center | And 2 more authors.
PLoS ONE | Year: 2017

Giant clams (tridacnine shellfishes) are large bivalves that inhabit tropical and subtropical waters and harbor the symbiotic microalgae zooxanthellae, which consist of diverse phylotypes (clades). Each clade exhibits unique physiological characteristics, and the cladal composition may influence the host's survival and its ability to tolerate environmental changes. Using quantitative PCR (qPCR) assays, we investigated the zooxanthellal genetic clades in Tridacna crocea (n = 93) and Tridacna squamosa (n = 93). These two clam species were artificially bred and maintained for an extended time period under an equivalent environment in an outdoor pond. Results showed that T. crocea had a simpler cladal composition and with an apparent dominance of clade A, whereas multiple clades were present in T. squamosa. The zooxanthellae clade A is known to occur in other zooxanthellae-bearing animals that inhabit shallow waters, which is consistent to the shallow water habitat preference of T. crocea. Interestingly, in larger individuals of T. squamosa, the main zooxanthellal clade was C rather than A. The mechanism underlying the dominance of clade C in the larger T. squamosa has not yet been clarified. However, the additional photosynthates supplied by clade C may be preferable for growing clams, as is observed in corals. The cladal composition of giant clams has previously been reported to be primarily controlled by environmental factors. However, our experiments subjected different clam species to the same environmental conditions, and our results suggested that species-intrinsic and/or growth-related processes may also influence the cladal composition. © 2017 Ikeda et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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.

Murata R.,University of Ryukyus | Kobayashi Y.,University of Ryukyus | Kobayashi Y.,Okayama University | Karimata H.,Okinawa Prefectural Sea Farming Center | And 4 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.

PubMed | Okinawa Institute of Science and Technology, Meiji University, University of Ryukyus and Okinawa Prefectural Fisheries Research and Extension Center
Type: Journal Article | Journal: DNA research : an international journal for rapid publication of reports on genes and genomes | Year: 2016

The brown alga, Cladosiphon okamuranus (Okinawa mozuku), is economically one of the most important edible seaweeds, and is cultivated for market primarily in Okinawa, Japan. C. okamuranus constitutes a significant source of fucoidan, which has various physiological and biological activities. To facilitate studies of seaweed biology, we decoded the draft genome of C. okamuranus S-strain. The genome size of C. okamuranus was estimated as 140 Mbp, smaller than genomes of two other brown algae, Ectocarpus siliculosus and Saccharina japonica Sequencing with 100 coverage yielded an assembly of 541 scaffolds with N50 = 416 kbp. Together with transcriptomic data, we estimated that the C. okamuranus genome contains 13,640 protein-coding genes, approximately 94% of which have been confirmed with corresponding mRNAs. Comparisons with the E. siliculosus genome identified a set of C. okamuranus genes that encode enzymes involved in biosynthetic pathways for sulfated fucans and alginate biosynthesis. In addition, we identified C. okamuranus genes for enzymes involved in phlorotannin biosynthesis. The present decoding of the Cladosiphon okamuranus genome provides a platform for future studies of mozuku biology.

Ohta I.,Okinawa Prefectural Fisheries Research and Extension Center | Ebisawa A.,Okinawa Prefectural Fisheries Research and Extension Center
Environmental Biology of Fishes | Year: 2016

The demography and sexual pattern of the white-streaked grouper, Epinephelus ongus (Serranidae), in the Yaeyama Islands, Okinawa, were examined based on age assessment using otoliths and gonadal histology. The von Bertalanffy growth parameters were estimated as follows: L∞ = 34.35 cm total length (TL); K = 0.187 yr. −1; and t0 = − 0.975 yr. The maximum age was 20 yrs. The smallest mature female was 18.9 cm TL, and the age of females at 50 % maturity was estimated to be 3.3 yrs. There were significant differences between sexes in size and age, with males (mean ± SD: 29.2 ± 3.3 cm TL, 9.0 ± 2.7 yr) being larger- and older than females (23.5 ± 3.4 cm TL, 5.9 ± 1.8 yr) Inactive bisexuals appeared in intermediate size and age between both sexes, suggesting that bisexuals were essentially recognized as being in a transitional phase from functional female to male. These facts indicated a monandric protogynous hermaphrodite of the species. Furthermore, transitionals were found only in the non-reproductive period that precedes the spawning aggregation period, indicating that the timing of the sex change has seasonality. © 2016 Springer Science+Business Media Dordrecht

Ebisawa A.,Okinawa Prefectural Fisheries Research and Extension Center
Fisheries Science | Year: 2013

The life history of the leopard coralgrouper Plectropomus leopardus was examined for the purpose of stock evaluation and to help maintain populations in the Okinawa Islands, southwestern Japan. Age was estimated from cut and burnt otoliths, and gonads were observed histologically to reveal the growth, spawning period and relationships between age and both sexual development and sexual maturation for P. leopardus in waters north of Okinawa Island. The three parameters in the von Bertalanffy growth equation, L ∞, k, and t 0, were estimated at 61.2 cm fork length, 0.289, and 0.41, respectively. The oldest individual obtained among the specimens was 18.8 years. The spawning period started in May and lasted until July. During this period, 50 % of females reached maturity at 43.3 cm fork length and at 5 years of age. Due to the sexual transition from female to male, the sex ratio decreased to 50 % at 59.8 cm fork length and at 10.3 years of age. © 2013 The Japanese Society of Fisheries Science.

Ohta I.,Okinawa Prefectural Fisheries Research and Extension Center | Ebisawa A.,Okinawa Prefectural Fisheries Research and Extension Center
Environmental Biology of Fishes | Year: 2015

The reproductive biology of the white-streaked grouper Epinephelus ongus, which forms spawning aggregations in the Yaeyama Islands, Okinawa, was examined by gonadal histology and oocyte development analysis. Gonadal histology showed that the spawning season was determined from April to July, but there are two spawning periods associated with the specific lunar cycle, during the week after the last quarter moon in two consecutive months. The pattern of oocyte development indicated that individual females spawned more than once, but fecundity may be determinate within a single spawning period. Fecundity was correlated to body size and ranged from several hundred thousand to a million eggs. Detailed catch data analysis showed that the catches during the two spawning months accounted for about 40 % of the annual landings and the fluctuation of the catch data corresponded well to some reproductive activities related to spawning aggregation. The two stepwise increases and the peaks of the catches coincided with the occurrence of matured individuals and the onset of spawning at the last quarter moon, respectively. These findings suggest that the spawning of E. ongus was concentrated within a few days just after the last quarter moon and that aggregation fishing was also concentrated in the critical reproductive periods. © 2015, Springer Science+Business Media Dordrecht.

Akita Y.,University of Ryukyus | Akita Y.,Okinawa Prefectural Fisheries Research and Extension Center | Tachihara K.,University of Ryukyus
Fisheries Science | Year: 2014

Age, growth, maturity, and sex changes of the monogrammed monocle bream Scolopsis monogramma were estimated from ca. 500 specimens collected at Okinawa-jima Island in southern Japan. Age was determined from sectioned otoliths: maximum ages were 10 years for females and 9 years for males. Parameters for von Bertalanffy growth functions were L t = 206.6{1 - exp[-0.68(t + 0.81)]} (n = 337) for females and L t = 244.4{1 - exp[-0.93(t + 0.32)]} (n = 130) for males. The spawning season was estimated to last from June to July, with a peak in July. The standard length (SL) and age at 50% maturity for females were estimated as 186.4 mm SL and 3.3 years, respectively. Intersex individuals appeared from 159.6 to 237.5 mm SL (n = 16) in fish between 1 and six years old, with the highest frequencies occurring at 170 mm SL and 2 years old. Hence, almost all S. monogramma specimens found at Okinawa-jima Island exhibited pre-maturational sex change, although some may have been protogynous hermaphrodites. Biological characteristics such as age at growth, maturation, and spawning season are valuable factors that can inform the resource management of local fisheries. © 2014 The Japanese Society of Fisheries Science.

Uehara M.,University of Ryukyus | Uehara M.,Okinawa Prefectural Fisheries Research and Extension Center | Tachihara K.,University of Ryukyus
Environmental Biology of Fishes | Year: 2014

Accurate descriptions of reproductive profiles are important for effective conservation and stock assessment efforts. We examined the reproductive traits of an Okinawan population of western Pacific gizzard shad (Nematalosa come) using histological analyses. The observed lengths at 50 % maturity were approximately 180 mm standard length (SL) for females and 130 mm SL for males, which corresponded to 4-year-old fish for females and at least 2-year-old fish for males. The spawning season was estimated to occur from January to August, peaking from March to June, with active spawning occurring during an increase in seawater temperature. The lipidosomatic index of both sexes decreased until June, presumably as the fish expended energy to spawn. The fecundity (F) of females, tested using 62 ovaries, was related to SL: F = 3.471 × 10−2 × SL3.122. The Okinawan population of N. come had a longer spawning season and a higher fecundity than other populations for which these data are available. Such favorable traits may contribute to the persistence of this population at the species’ distributional margin. Our findings indicate that the spawning seasons of Okinawan populations of N. come and Nematalosa japonica overlapped, implying that hybrid production occurs under natural conditions. Around Okinawa Island, however, the extent of shallow waters is rapidly decreasing because of recent land reclamation. We suggest the diminution of suitable sites as a possible factor for narrowing spawning opportunities and promoting the recent appearance of natural hybrids. Shallow habitats should be conserved to preserve healthy populations of the species. © 2014, Springer Science+Business Media Dordrecht.

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