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Ishizaki D.,Mie University | Mukai T.,Gifu University | Kikko T.,Shiga Prefecture Fisheries Experimental Station | Yodo T.,Mie University
Ichthyological Research | Year: 2015

Rhinogobius similis a common goby, widely distributed in Far East Asia, is characterized by an amphidromous life history, adult fish inhabiting the lower reaches of rivers, and larvae in the freshwater area being swept downstream to the sea and returning to the river following a period of pelagic marine existence. Individuals were collected from 6 stations in the Ibi, Nagara and Kamo Rivers, central Japan, and their otolith strontium and calcium environmental signatures examined using electron probe microanalyses. The otolith Sr:Ca ratios of R. similis from the Kamo River suggested a typical amphidromous life history, whereas those of fish collected from the Ibi River suggested two types of migratory life history pattern: amphidromous and river resident. In contrast, the otolith Sr:Ca ratios of fish collected at two stations upriver of a dam in the Nagara River estuary suggested an artificially landlocked life history. Emergent plant vegetation in the lower reaches of the Ibi River created slow currents and pools in the river, thereby possibly enhancing the likelihood of a river resident life history. In the Nagara River, however, landlocked specimens had been obstructed in their downstream migration by the dam. It is suggested that R. similis in central Japan has a variable migratory life history pattern, allowing the species to persist in upstream habitats in large rivers. © 2015 The Ichthyological Society of Japan

Kikko T.,Shiga Prefecture Fisheries Experimental Station | Kitakado T.,Tokyo University of Marine Science and Technology | Ishizaki D.,Shiga Prefecture Fisheries Experimental Station | Ujiie M.,Shiga Prefecture Fisheries Experimental Station | And 7 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2015

To estimate the catch of Honmoroko Gnathopogon caerulescens by recreational anglers around Ibanaiko lagoon, which is adjacent to Laka Biwa, for effective fisheries management, we randomly interviewed anglers from March to May 2012 and 2013. The number of Honmoroko caught by anglers was estimated using a two-stage sampling design; fishing days were samples for the first stage, anglers for the second stage, and we conducted a creel census of anglers. The estimated number of Honmoroko caught by anglers around Ibanaiko Lagoon was 272,275 (coefficient of variation=14%) in 2012 and 85,489 (CV=13%) in 2013. This study yielded useful information for the assessment and management of Honmoroko in Lake Biwa.

Kasai A.,Kyoto University | Kasai A.,Hokkaido University | Ishizaki D.,Shiga Prefecture Fisheries Experimental Station | Isoda T.,Shiga Prefecture Fisheries Experimental Station
Fisheries Science | Year: 2016

Diet-switch experiments with three different species of microalgae were conducted to estimate diet-tissue isotopic fractionation of carbon (C) and nitrogen (N) isotopes in the freshwater clam Corbicula sandai. The δ13C and δ15N values in the soft tissues of C. sandai changed in each experiment, with little inter-individual deviations, thereby reflecting the switch in diet. Isotope values of the clam reached the asymptotic value at around 40 days after the switch. Equilibrium isotopic signatures, as well as turnovers of carbon and nitrogen in the whole soft tissues, were estimated by exponential decay models. Fractionations for C. sandai varied from 0.1 to 0.7 ‰ for carbon, and from 2.1 to 3.6 ‰ for nitrogen; these values fell within or were close to the range of previously accepted fractionation values (0–1 ‰ for carbon and 3–4 ‰ for nitrogen). The half-life values for carbon in the bivalves (12–22 days) were about twofold longer than those for nitrogen (7–9 days). The specific fractionation values estimated in this study contribute towards improving our understanding of inter-specific trophic relationships and aquatic food webs. © 2016 Japanese Society of Fisheries Science

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