The migratory histories of individual masu salmon Oncorhynchus masou collected from the Naka River, Tochigi, Japan were clarified from otolith strontium (Sr) and calcium (Ca) concentrations using X‒ray electron microprobe analysis. Mapping and line analysis indicated three migratory types of the species. In addition to the conventional types, such as freshwater resident and typical anadromous (spending one year in marine waters), a new migratory pattern of short marine term anadromous (remaining in marine waters for several months) was apparent. Detailed life histories of short marine term anadromous individuals were estimated from otolith Sr fluctuations and ageing, from both scale and otolith daily increments. Consequently, more than half of the Naka River population was estimated to migrate to a marine environment upon reaching a total length of 178‒252 mm (one year old) in December‒January, thereafter staying in marine waters for approximately five months, before returning to the river in May‒July at 345‒463 mm total length. These findings may help establish an enhancement method for this species as a recreational fishery stock. Future investigations, including tagging, verification of age evaluation methods, and gene analysis are necessary to confirm the existence of the short marine term anadromous form.
Seven specimens of Tylerius spinosissimus (Regan, 1908) were washed up by a typhoon onto a beach at Nakagusuku in Okinawa-jima Island on 17 August 1997. This species has been rarely collected, being known from only a few localities in the tropical Indo-West Pacific. In addition to the seven specimens from Okinawa-jima Island, eight specimens collected off northwestern Borneo in the South China Sea by TV Oshoro-maru in November 1973 were found in the fish collection of the Hokkaido University Museum, Hakodate. Examination of the 15 specimens have revealed that the species is distinguished from other pufferfishes by the following characters: dorsal-fin rays 9–11, anal-fin rays 6–7, pectoral-fin rays 15–17, body somewhat squarish in cross-section, snout short with dorsal surface dropping abruptly anterior to eye, nasal organ a short papilla with two nostrils, eye dorsally adnate only, ventrolateral skin fold absent, body anterior to anal-fin base densely covered by small spinules, dorsal and ventral lateral lines running on lateral surface of body; frontals broad across interorbit, almost completely covering dorsal surface of ethmoid; prefrontal strongly down-curved. A juvenile of Tylerius spinosissimus ca. 10 mm in total length was photographed at 1 m depth in Suruga Bay, on the west coast of the Izu Peninsula, Honshu, Japan, in November 2008. This small specimen was similar in color to adults of T. spinosissimus: the dorsal half of the body being brown with a dark brown blotch just behind the dorsal corner of the eye, the ventral half of body white, and all fins pale.
A new fish-way, comprising variously-sized bed materials on a gentle slope, established on the Onga River estuary barrage was found to have 69 cobbles and boulders used as spawning nests of six goby species, including a threatened species, during the period from June 2013 to May 2014. Male body sizes were positively correlated with spawning substrate. In addition, wide salinity variations recorded over the fish-way during high tides on either side of spring tide were also implicated in goby spawning site selection.
Vertebral numbers in white-spotted charr (Salvelinus leucomaenis), collected from four streams and two lakes on Hokkaido Island, Japan, were significantly higher in fish from streams flowing into the Sea of Japan compared with those flowing into the Pacific Ocean, a result compatible with previous allozyme studies. White-spotted charr in Lake Shikotsu had the lowest number of vertebrae, possibly resulting from long-term isolation. The maximum difference in mean vertebral numbers among charr populations was 1.6, twice that observed in chum salmon Onchorhynchus keta and a possible reflection of the absence of hatchery programs that can lead to population mixing. It is likely, therefore, that regional genetic structures have been maintained in Hokkaido Island whitespotted charr.