A monogamous pipefish has the same type of ovary as observed in monogamous seahorses

Abstract

Syngnathid fish (pipefish and seahorses) are unique among teleost fish in that their ovary consists of a rolled sheet with germinal ridge(s) on the dorsal side running along the entire length of the sheet. A distinct difference is seen in the ovarian structure between polygamous Syngnathus pipefish and monogamous seahorses ( Hippocampus spp.), the former having one germinal ridge and the latter with two ridges. This study examined the ovarian structure and the mode of egg production in a monogamous pipefish Corythoichthys haematopterus . The ovary of C. haematopterus had two germinal ridges like that observed in monogamous seahorses. There were two distinct groups of follicles in the ovary, one being a cohort of extremely small follicles and the other a cohort of follicles developing and increasing in size with the passage of time. We suggest that the ovarian structure and the mode of egg production in this pipefish are adaptations to monogamy.

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

“…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.…”

“…Double germinal ridges have been observed in both Gastrophori and Urophori species. Sogabe et al (2008) suggested that the type of syngnathid egg production is closely related to species mating pattern, as monogamous and polygamous species produce eggs synchronously and asynchronously, respectively. However, few histological studies of syngnathids have been undertaken, and more investigations are required to understand the relationship between the mechanism of the ovary and the reproductive system.…”

“…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.…”

Basic reproductive biology of the barbed pipefish Urocampus nanus (Syngnathidae) under laboratory conditions

“…On the other hand, others (e.g. Corythoichthys haematopterus, Hipppocampus erectus, Microphis leiaspis, Nerophis ophidion) have ovaries that consist of two germinal ridges, one at each edge of the follicular sheet, and produce mature eggs discontinuously and synchronously (Selman et al 1991;Ishihara and Tachihara 2008;Sogabe et al 2008;Sogabe and Ahnesjö 2011). Furthermore, the latter is subdivided into two types differing in the frequency of ovulation; one ovulates eggs multiple times before spawning, but others do so at once before spawning.…”

“…In addition, the possibility that these females ceased to invest in reproduction because of poor body conditions caused by an inadequate food supply could not be denied. It has been reported that there is a distinct difference in the ovarian structure and mode of egg production among syngnathids (Sogabe et al 2008;Sogabe and Ahnesjö 2011). Some species (e.g.…”