Reproduction and early development of a freshwater pipefish Microphis leiaspis in Okinawa-jima Island, Japan

Abstract

We investigated the size at maturation, breeding season, and morphological development of larvae and juveniles of a freshwater pipefish Microphis leiaspis, which belongs to Gastrophori, collected from three rivers on the northern part of Okinawa-jima Island, Japan. The minimum size of brooding males was 105-123 mm in standard length (SL). The smallest mature female was estimated to be ca. 130 mm SL from the analysis of gonadosomatic index (GSI) and histological observations of gonads. The breeding season was estimated to be from June to December according to monthly changes in female GSI, histological observations of gonads, and monthly changes in the occurrence of brooding males. The number of eggs in the male brood pouch ranged from 75 to 241 (mean ± SD: 152 ± 52, n = 22). The male releases newly hatched larvae in freshwater areas. After newborns grow in the sea, they return to freshwater areas of the rivers and attain maturity. Microphis leiaspis was conformed to have an amphidromous life history. Notochord length of the released larvae was 6.1 mm, with a well-developed finfold. Larvae attained 11.1 mm SL, formation of the caudal and dorsal fin rays was complete, and the caudal fin became lozenge shaped at 30 days after the release, and juveniles reached 36.0 mm SL at 63 days after release. In the period between 30 and 63 days after the release, formation of all fins except the pectoral fins was completed, and caudal fin rays were extended and sector shaped with deep slits between each fin ray. The morphology of the released larvae of M. leiaspis is similar to that of Gastrophori species, and the morphology of juveniles similar to other species of Microphis.

The maturity and breeding season of the bellybarred pipefish, Hippichthys spicifer, in Okinawa-jima Island rivers

“…The breeding season of many syngnathids is early spring to late fall (Takahashi et al 2003). The oceanic syngnathid Corythoichthys haematopterus breeds from spring to autumn around Okinawa-jima Island (Takano, personal communication), and the breeding season of Microphis leiaspis, which inhabits the freshwater zone of rivers, is between June and December on the island (Ishihara and Tachihara 2008). However, we also expect the breeding season of H. cyanospilos, which inhabits seagrass beds, to be year-round in Okinawa-jima Island (our unpublished data).…”

“…In the case of Syngnathus scovelli, a Urophori also has a single germinal ridge Wallace 1987, 1988). However, the ovaries of Urophori Hippocampus erectus (Selman et al 1991) and C. haematopterus (Sogabe et al 2008) and Gastrophori Microphis leiaspis (Ishihara and Tachihara 2008) have double germinal ridges. Double germinal ridges have been observed in both Gastrophori and Urophori species.…”

“…4). In Microphis leiaspis, vitellogenic oocytes appeared only in mature females during the breeding season (Ishihara and Tachihara 2008). The estimated size at maturity of male Hippichthys spicifer was about 108 mm SL, and that of the female was about 100 mm SL.…”

“…In some syngnathids, the operational sex ratio is biased toward females, which compete with each other to mate with males (Berglund et al 1986;Jones and Avise 1997). The types of ovary structure and the relationship between egg production and the mating system have also been discussed (Begovac and Wallace 1987;Selman et al 1991;Ishihara and Tachihara 2008;Sogabe et al 2008). Comparative studies of the reproductive biology and life-history aspects of syngnathids are scarce.…”

Conserving migratory species under human impacts and climate change

“…Trait data were extracted from a published online database (Froese & Pauly, 2015) and previous studies (Ishihara & Tachihara, 2008;Jenkins & Jupiter, 2011;Maie, Schoenfuss & Blob, 2012;Gupta, 2016). We applied Generalized Gower's distance matrix after Pavoine et al (2009) to assess similarities among species, in which feeding guilds, habitat preference and climbing ability were binary variables, and life history was a categorical variable.…”