An in-depth knowledge of the reproductive biology of the different fish species can provide a sound scientific advice to set up fisheries management, in order to guarantee sustainability and prevent the resources collapse. European hake (Merluccius merluccius) is the second most important demersal fish species in the Mediterranean Sea, in terms of abundance and economic value and it is experiencing high fishing pressure, resulting in critical overexploited status. In this scenario, the aim of the study was to characterize, for the first time in the Northern and Central Adriatic Sea (GSA17), the reproductive biology of males of M. merluccius, that, unlike females, are currently poorly investigated. Wild European hakes males were randomly sampled throughout the year, to evaluate somatic indices and perform histological analysis. Three additional sampling were carried out on board of bottom trawler fishing vessels in order to take fresh samples (pituitary gland, testis and blood) and perform steroid immunoassay and qPCRs. A new reference scale was set ad hoc for this species. Five stages were distinguished by specific macroscopic and histological features: immature, developing, early spermiogenesis, late spermiogenesis and regenerating, surprisingly, no resting period was detected. The reproductive biology was more thoroughly investigated studying how the brain-pituitary-gonad (BPG) axis acts at different maturity stages. In particular, in pituitary the gonadotropin-releasing hormone receptor 2a (gnrhr2a) showed to be involved at the beginning of sexual maturity. Gonadotropins (fshb and lhb) progressively increased among the stages and peak in late spermiogenesis, suggesting that both hormones play an ongoing role, probably because M. merluccius is a multiple spawner with asynchronous testis. In all the stages prior to late spermiogenesis, lhb showed lower values than fshb, probably because lhb acts subsequently. In the testis, fshr and lhr showed earlier expression respect their ligands, presumably to guarantee the presence of the receptor upon arrival of the gonadotropins. Gonadotropins control steroidogenesis thus through androgens, whose mechanism of action is still not clear in the reproduction of fish males. The plasma levels of 11-ketotestosterone showed a gradual increase over the course of the reproductive cycle until reach the maximum in late spermiogenesis. This result can explain the expression pattern of alpha androgen receptor (ar?) in testis, that peaked in late spermiogenesis stage, perhaps to better respond to the paracrine hormonal stimuli of 11-KT. According to our previous study carried out on females, in GSA17 this species showed only one peak in spring-summer, as indicated by the highest values of gonadosomatic index (GSI) of males, registered between April and July. The reduced bathymetry of sampling could cause the absence of the winter peak, recorded in other geographic areas, since M. merluccius moves to deeper water in winter.
A MULTIDISCIPLINARY APPROACH TO INVESTIGATE THE REPRODUCTIVE BIOLOGY OF EUROPEAN HAKE ( Merluccius merluccius ): THE STUDY CASE OF MALES
Alberto Santojanni;Sabrina Colella;
2022
Abstract
An in-depth knowledge of the reproductive biology of the different fish species can provide a sound scientific advice to set up fisheries management, in order to guarantee sustainability and prevent the resources collapse. European hake (Merluccius merluccius) is the second most important demersal fish species in the Mediterranean Sea, in terms of abundance and economic value and it is experiencing high fishing pressure, resulting in critical overexploited status. In this scenario, the aim of the study was to characterize, for the first time in the Northern and Central Adriatic Sea (GSA17), the reproductive biology of males of M. merluccius, that, unlike females, are currently poorly investigated. Wild European hakes males were randomly sampled throughout the year, to evaluate somatic indices and perform histological analysis. Three additional sampling were carried out on board of bottom trawler fishing vessels in order to take fresh samples (pituitary gland, testis and blood) and perform steroid immunoassay and qPCRs. A new reference scale was set ad hoc for this species. Five stages were distinguished by specific macroscopic and histological features: immature, developing, early spermiogenesis, late spermiogenesis and regenerating, surprisingly, no resting period was detected. The reproductive biology was more thoroughly investigated studying how the brain-pituitary-gonad (BPG) axis acts at different maturity stages. In particular, in pituitary the gonadotropin-releasing hormone receptor 2a (gnrhr2a) showed to be involved at the beginning of sexual maturity. Gonadotropins (fshb and lhb) progressively increased among the stages and peak in late spermiogenesis, suggesting that both hormones play an ongoing role, probably because M. merluccius is a multiple spawner with asynchronous testis. In all the stages prior to late spermiogenesis, lhb showed lower values than fshb, probably because lhb acts subsequently. In the testis, fshr and lhr showed earlier expression respect their ligands, presumably to guarantee the presence of the receptor upon arrival of the gonadotropins. Gonadotropins control steroidogenesis thus through androgens, whose mechanism of action is still not clear in the reproduction of fish males. The plasma levels of 11-ketotestosterone showed a gradual increase over the course of the reproductive cycle until reach the maximum in late spermiogenesis. This result can explain the expression pattern of alpha androgen receptor (ar?) in testis, that peaked in late spermiogenesis stage, perhaps to better respond to the paracrine hormonal stimuli of 11-KT. According to our previous study carried out on females, in GSA17 this species showed only one peak in spring-summer, as indicated by the highest values of gonadosomatic index (GSI) of males, registered between April and July. The reduced bathymetry of sampling could cause the absence of the winter peak, recorded in other geographic areas, since M. merluccius moves to deeper water in winter.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
