THE POSSIBILITY OF ARTIFICIAL PROPAGATION IN FARMED STELLATE STURGEON, ACIPENSER STELLATUS

This study was conducted at the International Sturgeon Research Institute from the summer of 2003 through the summer of 2007 on 5 and 6 year-old farmed Acipenser stellatus specimens. A total of 32 farmed A. stellatus specimens (12 male + 20 female) were stocked in groups of 4 in eight fiberglass tanks (4 tons capacity) on the basis of their sexual maturity. Males in stage I and II of sexual maturity were fed diets without soybean and without vitamins, males in stage III-IV of sexual maturity were fed diets without soybean but containing vitamins. Females in stage II of sexual maturity were fed diet containing soybean, without vitamin and females in stage III of sexual maturity were fed diets containing soybean and vitamins. The results of the study indicate that food composition (soybean and vitamins C and E) played a significant and positive role in the reproduction system of female. Significant effect of treatment (P0.05) was observed in nucleus circumference, oocyte circumference and ratio of nucleus diameter to oocyte diameter in female fish fed diets containing soybean and vitamin indicating progress in their sexual maturity. However in males, temperature was seen to be more effective in controlling sexual maturity. Suitable temperature regimes in terms of active feeding need to be implemented in the case of males. Evaluation of blood indices in the fish under study showed significant differences (P0.05) in serum osmolarity during different stages of sexual maturity in the different seasons studied. Significant differences were also detected in the concentration of ions (Na, K, Ca, and Mg) in females in stages II, III, and III-IV of sexual maturity. However decreasing trends were observed in the concentration of Ca in stage IV females during the different seasons which coincided with the progress in sexual maturity reaching a minimum in spring. Concentration of Mg showed fluctuations in different seasons in stage IV females with the progress in sexual maturity and reached a minimum in spring. Therefore these two factors may be considered as indices in determining sexual maturity in farmed A. stellatus. In males, in addition to Ca and Mg, fluctuations were also observed in Na concentrations, which reached a maximum in winter in stage III males, only to decrease again in spring. Irregular fluctuations were observed in Mg concentrations during different seasons, reaching a maximum in summer and winter and decreasing in spring and autumn. Similar trends were recorded for Na and Mg ions in stage III-IV males. However unlike in females, no significant differences were observed in the concentration of Ca in stage IV males. Variations of male hormones in final maturation were quite similar to that in females. Increasing trends in testosterone levels and decreasing trends in 17&#945-hydroxy progesterone coincided with gonad development in stage III males. Fluctuations were recorded for testosterone levels in stage IV males, which reached a minimum in spring and autumn and a maximum in summer and winter. Irregular variations were recorded in 17&#945- hydroxy progesterone levels in stage IV males which declined from summer to winter and increased in spring. It is evident from the results obtained that stage IV females showed significant variations in testosterone levels which simultaneously increased with the progress in gonad development and reached a maximum in spring. On the other hand declining trends were recorded for 17&#945- hydroxy progesterone which reached a minimum in spring. Therefore these two hematological factors may be considered as suitable physiological indices in staging gonadal development and determining final maturation in farmed A. stellatus when selecting suitable spawners for artificial breeding. As compared to females, testosterone and 17&#945- hydroxy progesterone levels in male breeders showed fluctuations during the early stages of development. Increasing trends were recorded for testosterone levels which coincided with the progress in gonad development and reached a maximum in spring. However declining trends were recorded for 17&#945- hydroxy progesterone which reached a minimum in spring. No significant differences were detected in testosterone and 17&#946-estradiol levels recorded before injection, 12 h after injection (coinciding with the second injection) and after ovulation. Farmed Acipenser stellatus breeders used for artificial breeding were injected a combination of GnRH following the two dose protocol (dose=10 &#956g/kginterval=6-12 h and ratio=20:80) in females and the single dose protocol (dose=20 &#956g/kg) in males. Significant differences were detected in serum osmolarity of females prior to injection, 12 h after injection (during second injection) after ovulation (24 h after injection), and in females that did not respond to injection and in serum osmolarity of males prior to injection, 6 h after injection, after spermeation (12 h after injection) and showing incomplete spermeation. Creation of broodstock, harvesting suitable ovules and the production of farmed caviar (2005 & 2006), harvesting viable sexual products from farmed specimens, successful artificial breeding programs in farmed A. stellatus using the micro incision method of the oviduct without sacrificing the spawner and producing offspring from farmed specimens in the years 2006 and 2007 are among the various successful achievements of the present study. This study places emphasis on applied research and commercialisation of the results of this research towards the development of artificial breeding and rearing in sturgeons to produce caviar and enhance sturgeon aquaculture in the country.