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Tomiyama T.,Fukushima Prefectural Fisheries Experimental Station | Tomiyama T.,Hiroshima University
Fisheries Science | Year: 2013

Predation on the Manila clam Ruditapes philippinarum by the non-indigenous moonsnail, Euspira fortunei, has had severe impacts on clam fisheries in some localities in Japan. This paper aims to reveal when and how many egg collars E. fortunei produce during the egg-laying season. To investigate the frequency of egg-collar production, 13 pairs of E. fortunei were reared in aquaria with natural seawater flowing from July to December 2009. Each pair produced only one or two egg collars during 1 day in October; thereafter, no egg collars were produced. The timing of egg collar production, estimated from observational information by fishermen in the field from 2004 to 2010, varied among years. The period between September 1 and the day of the initial observation of egg collars was positively correlated with the average water temperature in August, suggesting that water temperature can be used to predict the timing of egg collar occurrence. © 2013 The Japanese Society of Fisheries Science.

Tomiyama T.,Fukushima Prefectural Fisheries Experimental Station | Tomiyama T.,Hiroshima University | Uehara S.,Tohoku National Fisheries Research Institute | Uehara S.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kurita Y.,Tohoku National Fisheries Research Institute
Marine Ecology Progress Series | Year: 2013

Juvenile Japanese flounder Paralichthys olivaceus inhabit shallow sandy areas and consume chiefly mysids. Hatchery-reared P. olivaceus (ca. 100 mm in total length) released in stock enhancement programs also consume mysids. To examine whether stocking is implemented within the available carrying capacity, we assessed the feeding relationships among fishes, based on the stomach contents of fishes collected off the coast of Fukushima, Japan. Similarity in diet suggested that 10 species, particularly the poacher Occella iburia and nibe croaker Nibea mitsukurii were potential competitors of P. olivaceus juveniles for food. Large inter-annual variability in the abundance of these competitors was observed, suggesting variability in their consumption of mysids. The predominant mysid Orientomysis mitsukurii was abundant every year, and growth rates of wild P. olivaceus, estimated from otolith microstructure, were mostly high (>1 mm d-1), even in the year when wild P. olivaceus were highly abundant. In our statistical model, abundance of mysids and consumption of mysids by fishes significantly affected the growth rates of wild P. olivaceus but only accounted for a small proportion (i.e. explained 2.2 and 2.4% of variance, respectively) of the total compared to the body size of juveniles (30.0%) and bottom water temperature (4.5%). These results suggest that the productivity of mysids is usually high enough to support the production of mysid consumers, but exceptionally high abundances of wild P. oliva ceus or other competitors can reduce the available carrying capacity. In such a situation, stocking should be restricted so as not to reduce productivity of wild fishes. © Inter-Research 2013.

Variation of scales on the blind side of Pseudopleuronectes yokohamae in relation to sex, maturity and body size was examined. Immature males often have cycloid scales, while mature males have mostly ctenoid scales. Large females also often have ctenoid scales (but with fewer spines compared with males), and small females have mostly cycloid scales. The number of spines (ctenii) on the blind-side scale increases with body size in both sexes, indicating an ontogenetic change in scale morphology. As P. yokohamae spawn demersal eggs with males positioning themselves above the females on the ocular side, it is hypothesized that ctenoid scales on the blind side in mature males function for maintaining contact with females during spawning. © 2013 The Fisheries Society of the British Isles.

Tomiyama T.,Fukushima Prefectural Fisheries Experimental Station | Kurita Y.,Tohoku National Fisheries Research Institute
Aquatic Biology | Year: 2011

We investigated the diet and somatic condition of 5129 individual Japanese flounder Paralichthys olivaceus, 20 to 92 cm in total length, in the Joban area along the Pacific coast of Japan (36° 40' N to 38° 00' N) from 2001 to 2007. Japanese flounder with food in their stomachs (1668 individuals) consumed chiefly fishes (92% of stomach contents by weight). Predominant prey species were Japanese anchovy Engraulis japonica (54% of fishes by weight) and Japanese sandlance Ammodytes personatus (22%). Japanese anchovy were consumed by Japanese flounder year round except in March and April, when the anchovy migrate from the Joban area. In March and April, Japanese flounder frequently consumed Japanese sandlance, but only in the northern part of the Joban area (37° 20' N to 38° 00' N); Japanese flounder did not feed on this species and had less content in their stomachs in the southern area (36° 40' N to 37° 20' N), where the sandlance is absent. Somatic and hepatosomatic conditions of Japanese flounder in the northern area were better than those in the southern area in March and April, suggesting that such spatial and seasonal heterogeneities in prey availability affect the nutritional status of predators © Inter-Research 2011.

Freeman M.A.,University of Malaya | Yokoyama H.,University of Tokyo | Osada A.,Fukushima Prefectural Fisheries Experimental Station | Yoshida T.,Fukushima Prefectural Fisheries Experimental Station | And 2 more authors.
Journal of Fish Diseases | Year: 2011

Anglerfish from the genus Lophius are a globally important commercial fishery. The microsporidian Spraguea infects the nervous system of these fish resulting in the formation of large, visible parasitic xenomas. Lophius litulon from Japan were investigated to evaluate the intensity and distribution of Spraguea xenomas throughout the nervous system and to assess pathogenicity to the host and possible transmission routes of the parasite. Spraguea infections in L. litulon had a high prevalence; all fish over 403mm in standard length being infected, with larger fish usually more heavily infected than smaller fish. Seventy percent of all fish examined had some gross visible sign of infection. The initial site of development is the supramedullary cells on the dorsal surface of the medulla oblongata, where all infected fish have parasitic xenomas. As the disease progresses, a number of secondary sites typically become infected such as the spinal, trigeminal and vagus nerves. Fish with infection in the vagus nerve bundles often have simultaneous sites of infection, in particular the spinal nerves and along the ventral nerve towards the urinary bladder. Advanced vagus nerve infections sometimes form xenomas adjacent to kidney tissue. Spraguea DNA was amplified from the contents of the urinary bladders of two fish, suggesting that microsporidian spores may be excreted in the urine. We conclude that supramedullary cells on the hindbrain are the primary site of infection, which is probably initiated at the cutaneous mucous glands where supramedullary cells are known to extend their peripheral axons. The prevalence of Spraguea infections in L. litulon was very high, and infections often extremely heavy; however, no associated pathogenicity was observed, and heavily infected fish were otherwise normal. © 2011 Blackwell Publishing Ltd.

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