Juvenile migration of the exclusively pelagic cyprinid, Gnathopogon caerulescens (Honmoroko) in Lake Biwa, Central Japan

Abstract

Migration of wild and cultivated juvenile honmoroko Gnathopogon caerulescens of from the spawning and nursery areas in Lake Biwa were investigated, both in the Ibanaiko Lagoon and its outlet to Daido River, using beam-trawl surveys in 2013 and 2014. The study demonstrated migration of G. caerulescens from a nursery lagoon toward Lake Biwa after the juvenile stage. These findings appear to be the first direct evidence for migration of an exclusively pelagic cyprinid species from a littoral nursery to a pelagic adult habitat in a large deep lake.

Multipath ecological influence of an iteroparous fish migration from Lake Biwa to an alluvial stream

“…In this catchment, all fish spawn in the tributaries even if they are pelagic species of the lake (Yuma et al, 1998). Depending on the season, 46 native fish species migrate to the catchment (e.g., Fujioka & Kido, 2021; Ishizaki et al, 2016; Kikko et al, 2018; Maruyama et al, 2018; Tsuji et al, 2021). Three have been specifically examined: three‐lips ( Opsariichthys uncirostris uncirostris ) migrate during May–September (Maruyama et al, 2018); ayu fish ( Plecoglossus altivelis altivelis ) mainly migrate during September–November (Sawada et al, 2020); and Biwa trout ( Oncorhynchus rhodurus ) migrate during November–December (Fujioka & Fushiki, 1989).…”

Daily growth increments in otoliths of wild‐caught honmoroko Gnathopogon caerulescens

“…Individual G. caerulescens normally mature one year after hatching, dying at 1–2 years of age (Fujioka & Saegusa, ). They inhabit shallow estuaries during the larval and juvenile stages, moving to the pelagic zone as adults, determined from the recapture of alizarin complex one (ALC)‐marked fish (Kikko et al, ). Individuals migrate from the main lake to the lagoon and shoreline habitats for spawning, from April to July (Fujioka et al, ; Kikko et al, ; Kikko, Ishizaki, et al, ; Kikko, Usuki, et al, ).…”

“…In late May each year, previously marked juveniles were returned to ALC solution (16 mg l −1 ) for 24 h to stain the otolith, resulting in dot‐ring marked fish (Figure ). On May 24, 2013, 128,000 and 170,000 on May 22, 2014, dot‐ring marked juveniles were subsequently released into the inner part of Ibanaiko Lagoon (Kikko et al, ).…”

“…Gnathopogon caerulescens feed on zooplankton ( e.g . rotifers, the primary food of both G. caerulescens larvae and juveniles), the abundance of which under natural conditions, such as those of the Ibanaiko Lagoon, increases over spring and summer, suggesting favourable food availability during that time (Kikko et al, ). In addition, naturally occurring water temperatures were higher during spring and early summer compared with those of artificial ponds and probably more suitable for G. caerulescens early growth (Kikko, Usuki, et al, ).…”

“…Figure 2). On May 24, 2013, 128,000 and 170,000 on May 22, 2014, dot-ring marked juveniles were subsequently released into the inner part of Ibanaiko Lagoon(Kikko et al, 2018).Surveysof released ALC-marked fish were conducted from May to September in 2013 and 2014 using a 3.0 m beam trawl (0.5 m height, 5 m overall length, 0.5 cm mesh cod end), towed at 15 sampling stations by a boat during daytime (Figure 1, Kikko et al, 2018). Larval and juvenile G. caerulescens individuals were measured (L S , mm) and the otoliths (left lapillus) of all fish examined using a fluorescent microscope (Nikon Optiphot, XT-EFD; www.nikon.com) with G-filter (BM 520), so as to discriminate between wild-bred and released stocks based on the presence or absence of an ALC dot-ring.…”