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Seminal plasma indices (osmolality and ionic composition), spermatozoa concentrations and sperm motility were studied in the Persian sturgeon, Acipenser persicus in order to use these semen biomarkers to measure performance in terms of sequential stripping effects. Semen samples were collected by hand stripping from nine induced males injected intramuscularly with sturgeon pituitary homogenized extract at dosages of 50-70 mg Kg -1 body weight, 24h after spawning induction (first stripping), 12h after first stripping (second stripping) and 12h after second stripping (third stripping). The spermatozoa concentration and osmolality of the seminal plasma decreased significantly with subsequent stripping. The Na + , K + and Clions concentrations were predominate in the seminal plasma at different stripping times. But, there were no significant differences between ions concentrations at different stripping frequencies (P>0.05). The percentage of motile spermatozoa (after 15-30 sec post-activation) and total of period of sperm motility decreased significantly (P<0.05) when the stripping frequency increased, where the semen diluted in fresh water (control). Interestingly, the observed effects of stripping times on the sperm motility could overlap by manipulating of sperm activation medium. The results showed that sperm motility parameters significantly were increased in terms of percentage of motile spermatozoa and total periods of sperm motility compared to control (fresh water) after discharge of sperm into a solution with osmolality 50mOsmol Kg -1 at second and third strippings. Probably, the sequential stripping influences on sperm motility via enzymatic activities. Nevertheless, further studies are needed to understand the physiological relationships.

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Since sturgeons do not show clear sexual dimorphism, attempts were made to determine the best method to identify sex and gonadal stages in live fish. In this study we used two steroid hormones (testosterone (T) and estradiol (E2)) as well as several morphometric parameters such as total length (TL), fork length (FL), body weight and age (pectoral spines) to differentiate between sex and gonad developmental stages in Persian sturgeon, Acipenser persicus. Forty-seven fish were caught in southern and southeastern Caspian Sea. Blood was taken from each of the fish and Radioimmuno-assay (RIA) was performed to measure the levels of two hormones in blood sera. Gonads were dissected and prepared using hematoxylin-eosin method for sexing and staging. One-way analysis of variances (ANOVA), Bonferroni procedure and Discriminant function analysis (DFA) were used to process the data. Studied fish determined to be belonging to four groups of Stage II females, Stage IV females, Stage III males, Stage IV males. Plasma T (P=0.0090) and E2 (P=0.0001), weight (P=0.0001), TL (P=0.0058), FL (P=0.0019), and age (P=0.0088) differed significantly among the four groups of sex and stage of maturity. The stepwise DFA revealed that plasma T and E2 plus either age, TL, FL, or weight were the best predictors to distinguish Persian sturgeon by sex and stage of maturity with accurate classification of 86 to 100% and overall accuracy of 96% of all samples. Cross-validation of grouped predictors used showed a total accuracy of 91% for sex and gonadal stage discrimination. All the fish in stage II and stage IV female were correctly classified using the combined values of hormonal levels with any of the morphological or age measures. Associated amounts of three variables of T, E2 and FL found to be the best predictors of sex and gonadal stages with the lowest misclassification rate (7%) in the examined fish. In conclusion, this study introduces a less invasive and highly reliable approach to delineate the sex and gonad stage in Persian sturgeon.