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.

The availability of rotifer as live food is importance in a larval mariculture. Therefore a continuous and high production of rotifer is needed. The study was aimed to determine the frequency and dosage of the best food in rotifer culture. Nannochloropsis oculata, yeast and scott's emulsion are used as potential feeds for rotifer. Three dosages of N. oculata (150,000; 250,000, and 350,000 cells/ind.rotifer/day) were applied in the study and were given twice per day. Meanwhile, yeast(0.5 g/10 6 ind./day) and Scott's emulsion with different dosages (2, 4, and 8 µg/10 6 ind./day) were given with two different feeding frequencies (two and four times a day) for each dosages. Each treatment was done in triplicates. Sampling of rotifer was conducted in the morning (AM) and afternoon (PM). Water quality (temperature, dissolved oxygen and ammonia) was also measured. Growth and productivity of rotifer were determined from the number of rotifer and the number of rotifer eggs, respectively. The results showed that the optimum productivity of rotifer was achieved by giving N. occulata of 250,000 sel/ind/day, twice a day in four days culture. Meanwhile, treatment with yeast and Scott's emulsion gave best performance when applying 0.5 g/10 6 and 2 µg/10 6 ind./day twice per day, respectively. Yeast and scott's emulsion treatment yielded optimum production in two days of culture. ABSTRAK Ketersediaan pakan alami rotifer ditingkatkan ketersediaannya seiring dengan meningkatnya jumlah larva ikan laut, untuk itu diperlukan usaha guna meningkatkan produktifitasnya. Penelitian ini bertujuan untuk menentukan dosis dan frekuensi pakan terbaik dalam kultur rotifer. Nannochloropsis oculata, ragi dan scott's emulsion digunakan sebagai pakan rotifer. Dosis masing-masing pakan N. oculata adalah 150.000, 250.000 dan 350.000 sel/ind. rotifer/hari diberikan dua kali sehari. Sedangkan ragi sebanyak 0.5gr/10 6 ind./hari dan scott's emulsion dengan dosis 2, 4, dan 8 µg/10 6 ind./hari diberikan dengan frekuensi 2 kali sehari dan 4 kali sehari. Masing-masing perlakuan dikerjakan dengan tiga kali ulangan. Sampling dilakukan pada pagi dan sore hari. Dilakukan analisa kualitas air meliputi suhu, amoniak dan DO. Pertumbuhan dan produktifitas rotifer dianalisa melalui jumlah individu dan jumlah telur rotifer yang dihasilkan. Data yang diperoleh dianalisa secara diskriptif. Hasil Penelitian menunjukkan bahwa pakan N.oculata sebanyak 250.000 sel/ind./hari dengan frekuensi pemberian pakan 2 kali sehari merupakan dosis terbaik pada kultur rotifer dengan pakan N. oculata, pada kultur ini 4 hari merupakan waktu optimal untuk produksi. Sedangkan ragi sebanyak 0.5 gr/10 6 ind./hari dan scott sebanyak 2 µg/10 6 ind./hari dengan frekuensi pemberian pakan 2 kali sehari merupakan dosis terbaik pada kultur rotifer dengan pakan ragi dan scott's emulsion, waktu optimal produksi dengan metode ini selama 2 hari.