Histological Evaluation of Gonad Impairments in Russian Sturgeon (Acipenser gueldenstaedtii) Reared in Recirculating Aquatic System (RAS).

Małgorzata Rzepkowska,Dobrochna Adamek-Urbańska,Marek Łukasz Roszko,Magdalena Fajkowska

doi:10.3390/ani10081439

Abstract

Simple SummaryThe growing interest in sturgeon aquaculture necessitates the constant development of rearing techniques with special emphasis on the maintenance of high fish reproduction performance. However, there is a substantial lack of knowledge regarding gonadal impairments in sturgeons, even though the occurrence of such disorders poses a significant threat to the future of both commercial and conservation farming. Therefore, the aim of the research was to determine potential pathologies in the gonads of over-four-year old Russian sturgeon (Acipenser gueldenstaedtii) reared in the controlled conditions of recirculating aquatic systems (RAS). RAS have gained popularity in recent years, as they are considered the most environmentally friendly way of producing fish. Nevertheless, there are many issues that need to be resolved regarding sturgeon RAS farming, including its effect on gonadal development and, therefore, fish reproduction capacity. A detailed histological analysis revealed multiple gonadal disorders in the analyzed sturgeon, some of which can contribute to decreased fish fertility or even sterility. The female-biased sex ratio and the character of the identified impairments indicates that the observed germinal tissue disruptions might originate from estrogenic endocrine disturbances. Therefore, for the further sustainable development of sturgeon RAS aquaculture, there is an urgent need to identify and eliminate the causes of such disruptions.The aim of the study was to raise an issue concerning gonadal impairments in sturgeon reared in recirculating aquatic systems (RAS). In the present study, an in-depth histological evaluation in terms of gonadal pathologies was performed on over-4-year-old (1600 days post-hatching) Russian sturgeon (Acipenser gueldenstaedtii) reared under indoor RAS. A female-biased sex ratio, intersex occurrence, ovarian fat overgrowth, T-cell infiltration and follicle atresia were the most commonly observed disorders in the analyzed gonads. The combined processes of oocyte autophagy and follicular cell apoptosis were engaged in follicular atresia; however, atretic follicles showed a varied morphology, whereas oogonia and oocytes in the early stages of meiosis, as well as spermatogonia, underwent degeneration by apoptosis. The most severe pathology was observed in females with abundant intra-ovarian fat deposition. The extremely fatty ovaries were noted to lose the majority of ovarian follicles, which directly leads to fish sterility. The identified impairments might be related to estrogenic endocrine disruption, as feminization and unspecific vitellogenin synthesis were detected, although the sources of the observed pathologies can be diverse. Therefore, the presented research lays the groundwork for further studies on reproductive disorders in this prized and endangered fish species.

Highlights

From an economic point of view, sturgeons are fish of great value, being a source of caviar and meat production
Among the 15 analyzed Russian sturgeon, nine specimens were identified as females; five, as intersex; and only one, as male
Impaired gonadal development is an important issue for further sustainable sturgeon aquaculture development, surprisingly, only few pieces of research focusing on gonadal abnormalities in the sturgeon have been published to date, reflecting the insufficiency of the knowledge in this field

Summary

Introduction

From an economic point of view, sturgeons are fish of great value, being a source of caviar and meat production. Wild sturgeon populations have diminished greatly due to overfishing and poaching combined with water pollution and a loss of natural habitats. This has resulted in the current status of the Acipenseridae family as one of the most endangered among all animal species [1]. Recirculating aquatic systems (RAS) are considered as the most environmentally friendly way of producing fish at a commercially viable level, and sturgeons are one of the species of interest to be reared under RAS conditions [3]. There has been insufficient knowledge on the optimal conditions in terms of sturgeon RAS rearing, and general recommendations for sturgeon farming are often incomplete or inconsistent. The optimal sturgeon stocking density was estimated at 80–90 kg/m3 [8]

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