SPERMATOGENESIS IN WILD AND CAPTIVE-REARED GREATER AMBERJACK Seriola dumerili (RISSO, 1810)

Introduction

 Greater amberjack Seriola dumerili (Risso, 1810) is an excellent can didate  for  aquaculture thanks to its rapid growth, excellent flesh quality and worldwide market appreciation.  As other captive-reared fishes exhibiting reproductive dysfunctions (Zohar and Mylonas, 2001) , greater amberjack males produced  reduced sperm volume  with a decreased sperm quality.  The present work represents an overview of the results obtained in a comparative research study on the spermatogenesis of wild and captive-reared greater amberjack carried out in the framework of the EU FP7 project Diversify (www.diversifyfish.eu) (Zupa et al, 2017a, b).

Material and Methods

Twelve greater amber jack  males caught from the wild and reared in captivity  for three years  in a sea cage in Salamina  Island  (Greece) and 14 males caught from the wild around Pelagie Islands (Sicily, Italy) , were sampled during three phases of the reproductive cycle: early  spermatogenesis  (late April-early May), advanced spermatogenesis (late May-early June) and  spawning  (late June-July).  For each fish,  biometric data (fork length, FL, in cm; body mass, BM,  in kg ; testis mass,  TM, in g) were registered and gonadosomatic  index (GSI = 100 × TM/BM) calculated. T estis  samples were chemically  fixed and destined to  basic histological analysis and to the identification of proliferating and apoptotic germ cells through the immunohistochemical detection of the proliferating cell nuclear antigen (PCNA) and the TUNEL method, respectively. Blood samples  were centrifuged and plasma was collected and stored at -20°C for the analysis of 17β-estradiol (E2), testosterone (T), 11-ketotestosterone (11-KT) and 17,20β-dihydroxypren-4-en-3-one (17,20β -P)  by ELISA assays.

Results and Discussion

Captive-reared fish showed  lower  GSI  and  smaller seminiferous lobules compared to wild fish in all the three phases of the reproductive  cycle.

Anti-PCNA immunostaining was observed in the nuclei of spermatogonia and primary spermatocytes (Fig. 1a). All the captive-reared and most of the wild greater amberjack showed TUNEL-positive germ cells (Fig. 1b). Individuals reared in captivity  showed  a gradual  decrease of  germ cell proliferation throughout the  three reproductive phases, which led to a precocious cessation of the spermatogenesis as well as a higher germ cell apoptosis in early spermatogenesis . In all three reproductive phases, captive-reared fish showed lower  T, 11-KT and 17,20β-P  plasma concentration s  compared to wild fish ; however, captive-reared fish showed a  many-fold higher E2  plasma levels  during the  early spermatogenesis.

The  occurrence of  a  severe endocrine dysfunction was described in  captive-reared  greater amberjack males, including low T, 11-KT and 17,20β-P plasma levels during all the examined spermatogenesis phases. Abnormally high E2 plasma concentrations were associated to an increased germ cell apoptosis during early spermatogenesis .  The observed reproductive dysfunction finally led to  a  lower  sperm concentration and quality (Zupa et al., 2017a ). A s evere  impairment of the  reproductive function was observed also in females of the same broodstock  and involved low steroid plasma concentrations and extensive atresia of late vitellogenic oocytes (Zupa et al., 2017b ).  Preliminary data obtained within the H2020 project NewTechAqua indicate that hatchery-produced greater amberjack  males  reared in sea cages in Salamina (Greece) have similar GSI compared with wild fish sampled in the same period of the reproductive cycle (early June 2021). Although further analyses are required, the available data  seem to suggest that the reproductive function  might  be less affected by captivity-induced stress in  hatchery-produced  greater amberjack than in wild-caught breeders.

 Financial grant provided by the  European Union´s Programmes FP7 (GA 603121, DIVERSIFY) and H2020 (GA 862658 , NewTechAqua).

References

Zohar, Y., Mylonas, C. C. 2001. Endocrine manipulations of spawning in cultured fish: from hormones to genes. Aquaculture, 197: 99–136.

 Zupa, R., Fauvel , C., Mylonas, C. C., Pousis, C., Santamaria, N., Papadaki, Μ., Fakriadis, I., Cicirelli, V., Mangano, S., Passantino, L., Lacalandra, G. M., Corriero, A. 2017a .  Rearing in captivity affects spermatogenesis and sperm quality in greater amberjack Seriola dumerili (Risso, 1810). Journal of Animal Science, 95: 4085-4100.

Zupa, R., Rodríguez, C., Mylonas, C. C., Rosenfeld, H., Fakriadis, I., Papadaki, M., Pérez, J. A., Pousis, C., Basilone, G., Corriero, A. 2017b . Comparative study of reproductive development in wild and captive-reared greater amberjack Seriola dumerili (Risso,1810).  PLoS ONE 12(1): e0169645.