Anatomical, hormonal and histological descriptions of captive Russian sturgeon (Acipenser gueldenstaedtii) with intersex gonads.

Sturgeons are known throughout the world as the source of black caviar. Their declining populations in their native habitats, mainly the Caspian Sea, due to over-fishing for meat and caviar production, destruction of their spawning grounds and water pollution, have led to their introduction into aquaculture in areas with suitable conditions, including Israel. Recently, we noticed an unusual phenomenon in these normally gonochoristic species. Several 5-year-old female sturgeons were found to have one or more testicular sections in each of their two gonads, forming an intersexual gender. Further examination of other fish from the same age group revealed 14% fish with intersex gonads among a population of 5000 fish that had been pre-selected as females. This phenomenon has not been found however in other age groups of Russian sturgeons, cultured at the same facility. Sturgeons are a generally gonochoristic species, and hermaphroditism is only very infrequently observed under natural or normal breeding conditions. Moreover, these rare cases have all been from polluted habitats. The present work is the first description of fish containing intersex gonads in Russian sturgeon (Acipenser gueldenstaedtii). We describe the phenomenon anatomically and histologically, and examine plasma steroid levels and pituitary gonadotropin gene expression by comparing fish with intersex gonads with normal females and males of the same age group. Intersex gonads were typical female ovaries with one or more white testicular components embedded in each. The testis components were not uniform in size or location among the two gonads of each fish or among different fish, and they showed marked differences in distribution. The ovarian component of the intersex gonad was at the pre-vitellogenic stage as in normal females, and the testis component contained spermatids and mature spermatozoa as in normal males of the same age. However, in terms of estradiol and 11-ketotestosterone plasma levels, as well as of pituitary gonadotropin (betaLH and betaFSH) gene-expression levels, the fish with intersex gonads were more similar to the normal males than to the normal females, even though the testis part of the intersex gonad was smaller than the ovarian part. To examine the possibility that the fish containing intersex gonads were hybrids, phylogenetic trees were constructed from the consensus sequences of Cytochrome b and control region (D-loop) genes. Results indicated no differences between the fish with intersex gonads and normal males or females of the same age group. However, statistically significant differences were found between different age groups of Russian sturgeon, as well as of white sturgeons (A. transmontanus), grown under the same culture conditions.