Reproductive strategies in macrourid fish:seasonality or not?

Abstract

Macrourid fish are abundantly found on the continental slope of the Ionian Sea (eastern Central Mediterranean), but the knowledge on their biology is still rather scanty. The reproductive stragegy of Hymenocephalus italicus, Nezumja sclerorhynchus and Coelorhynchus coelorhynchus was studied through data collected during 8 seasonal trawl surveys carried out between April 1996 and March 1998. Ripe females of H. italicus and N. sclerorhynchus were found all year round, with a small increase during summer and autumn in the former and without any seasonal component in the latter. Few ripe females of C. coelorhynchus were collected over the study period, with the exception of October 1996 when an increase was recorded, indicating that autumn could be included in the breeding season of this grenadier. The many different sizes of eggs and postovulatory follicles found in the ovaries indicate that all 3 species reproduce serially as multiple batch spawners. Maximum egg sizes were 1.5 mm in H. italicus and N. sclerorhynchus and 1.6 mm in C. coelorhynchus. The h~ghest gonadosomatic index values were found in H. italicus, and the lowest in C. c'oelorhynchus. All 3 species seem to delay reproduction. The size at first maturity (50% of the population) was 27 mm pre-anal length in H. italicus, 37 mm in N. sclerorhj/nchus and 61 mm in C. coelorhynchus. Aseasonal continuous spawning can be assumed for N. sclerorhynchus while the low frequency of the early maturity stages in H. italicus makes it difficult to state whether or not this macrourid spawns throughout the year without a seasonal component. Further study is necessary to define the reproductive cycle of C. coelorh ynch us.

Biology and ecology of Nezumia liolepis and N. stelgidolepis from the west coast of North America

“…Nezumia liolepis during October and November 1997 showed no evidence of gonadal development and most ovaries in the resting state. The single N. stelgidolepis with active ovaries suggests batch spawning spanning autumn, in common with other Nezumia species (D'Onghia et al, 1999). However, all other N. stelgidolepis had ovaries in the resting state resulting in only a tentative conclusion for time of spawning for this species.…”

Population structure, age and growth of macrourid fish from the upper slope of the Eastern‐Central Mediterranean

“…Although ripe female H. italicus were found all year round, the increase during summer and autumn, highlighted in D' Onghia et al (1999), may determine increasing abundance of recruits from autumn to spring, that is, the seasonal component in recruitment would derive from the seasonal component in the reproduction. In contrast to H. italicus, the reproductive cycle of N. sclerorhynchus displays no seasonal component (D'Onghia et al, 1999). This would explain the continuous occurrence of the year's young.…”

“…Although few ripe female C. coelorhynchus were collected over the study period, the presence of young-of-the-year in each season would confirm the spawning continuity during the year in this grenadier (D'Onghia et al, , 1999, even though a seasonal component in its reproduction still cannot be excluded.…”

Reproductive biology of three gadiform fish species through the Mediterranean deep-sea range (147-1850 m)

“…In the Mediterranean, other gadifirm species living in the upper-middle slope can present a continuous reproductive pattern as in Nezumia sclerorhynchus (D'Onghia et al, 1996(D'Onghia et al, , 1999(D'Onghia et al, , 2000, N. aequalis (Massutí et al, 1995) and Hymenocephalus italicus (Massutí et al, 1995;D'Onghia et al, 1996), a quasi-continuous strategy with a reproductive peak as in Coelorhynchus coelorhynchus (Massutí et al, 1995;D'Onghia et al, 1996D'Onghia et al, , 1999, or a seasonal pattern as in Trachyrhynchus trachyrhynchus (D'Onghia, 1996). The lower slope macrourid studied, Coelorhynchus labiatus, has an autumn-winter spawning (Massutí et al, 1995).…”