Ovarian dynamics, batch fecundity and spawning phenology of the lessepsian migrant Etrumeus golanii DiBattista, Randall & Bowen, 2012 (Clupeidae: Dussumieriinae)

Abstract

The Golani’s round herring Etrumeus golanii is an Erythraean small pelagic fish (lessepsian migrant) that entered into the Mediterranean Sea through the Suez Canal. It has expanded its distribution from the east to the western Mediterranean with well-established local populations. We investigated basic aspects of its reproductive biology off the island of Crete (eastern Mediterranean) using ovarian histology and analysis of oocyte size-frequency distributions. The species exhibited a protracted breeding period (winter to early summer), with all ovaries examined during the main spawning season having markers of recent (postovulatory follicles, POFs) or imminent spawning (advanced oocyte batch in germinal vesicle migration or hydration). The advanced batch (AB) increased rapidly in size and was fully separated from the remainder, less developed oocytes in 95% of females with “old” POFs (POFs with signs of degeneration) and all females in final maturation. The growth of the subsequent batch (SB) was arrested at sizes <630 µm until full maturation of the AB. Mean diameter of hydrated oocytes ranged from 1181 to 1325 µm and relative batch fecundity was low ranging from 56 to 157 eggs g-1. The simulation of a coupled hydrodynamic/biogeochemical model (POM/ERSEM) provided evidence that E. golanii takes advantage of the seasonal cycle of planktonic production to reproduce and exhibits monthly changes in batch fecundity that appear to be closely related with the seasonal cycle of mesozooplankton concentration.

Linking the dynamic organization of the ovary with spawning dynamics in pelagic fishes

“…In sardine, the spawning batch was separated from the SG pool since mid-vitellogenesis. A similar pattern is also reported for two other clupeids (Etrumeus teres: Plaza et al 2007; Etrumeus golanii : Somarakis et al 2021) in which the advanced batch grows rapidly after spawning and shortly separates from the smaller oocytes. In horse mackerel and mackerel, this separation took place at various phases of final oocyte maturation (FOM).…”

“…Accordingly, the link with spawning dynamics was investigated by evaluating various attributes of ovarian dynamics, including the oocyte size frequency distribution, the ratio of total to batch fecundity, the histological clustering of oocyte cohorts, and the recruitment pattern from primary growth to secondary growth, as expressed by the numerical ratio of early secondary growth oocytes (ESG)-on-late primary growth oocytes (LPG). These aspects were related to historic estimates of spawning interval which is a variable of paramount importance in biomass assessments of commercial fish stocks through egg production methods (Ganias 2013), especially the Daily Egg Production method (DEPM; Stratoudakis et al 2006;Somarakis et al 2012).…”

Quantitative Analysis of Ovarian Dynamics of European Sardine Sardina pilchardus (Walbaum, 1792) during Its Spawning Period

“…Schismenou et al [10] have also shown that in the European anchovy de novo vitellogenesis occurred in parallel with PG to SG recruitment, while Wallace and Selman [2] mentioned that in the daily spawner medaka fish (Oryzias latipes), during the recruitment of oocytes into maturation, a new clutch of oocytes was recruited into vitellogenesis. In Etrumeus golanii, Somarakis et al [16] found that the final maturation of the advanced batch triggered the recruitment of oocytes into the subsequent batch, and after ovulation they started rapidly to grow in size to form the new advanced batch, a pattern similar to the one described here.…”

“…All the GLM analyses were performed using backward stepwise selection and only significant terms (p < 0.05) were retained in the final models. All assumptions, i.e., normal distribution of errors and homogeneity of variance, were met [16,31,32]. When no significant model could be fitted, sample means were used.…”

“…Schismenou et al [10] using the above-mentioned methods showed that in European anchovy (Engraulis encrasicolus) the hydration of the advanced batch activates the recruitment of oocytes into vitellogenesis which occurs in rapid pulses of less than 24 h. Mouchlianitis et al [15] have found that in Alosa macedonica, another fish with indeterminate fecundity, oocyte recruitment from primary to secondary growth phase occurs in a stepwise manner in parallel with the ovulation, while Somarakis et al [16] showed that, in Etrumeus golanii, during the final maturation of the advanced batch, a new batch starts to recruit quickly to sizes > 500 µm and after ovulation, it grows rapidly to form the new advanced batch. However, such studies usually do not examine how these processes may change during the course of a protracted spawning period.…”