Today, the artificial reproduction of sturgeon fish is the only method to restore the stocks of these valuable species. The purpose of implementing this project is to determine the most suitable weight of the fish fry in order to release them directly into the river or sea mouth to prevent losses and reduce the cost and shorten the period of keeping the sturgeon fish in breeding centers. A. stellatus fish fry were loaded from Shahid Beheshti complex reproduction and restoration center and tested in 12 2 ton tanks with sea water, well water and their mixture with aeration with appropriate density. A number of 1200 A. stellatus fry at different ages of 55, 69, 77 and 85 days after hatching were stored with a density of 100 per square meter. A. stellatus fish fry were reared in four treatments including 55 days (0.5-1 g), 69 days (1-3 g), 77 days (3-5 g) and 85 days (5-10 g) in water. 4 experiments in different salinities (0.5, 5.4, 4.9 and 9.13) and each experiment was designed in 4 treatments and each treatment had 3 repetitions. Each experiment was carried out in a period of almost one month, along with feeding with live food, preferably Gamarus, nereis worm, Shironomide at the saturation level of 6 meals a day, and siphoning and changing water continuously. Biometry was done every 10 days. The results of the present study showed that the best breeding period for releasing baby fish into the sea (9-13 salinity) is during 77 and 85 days (3 to 5 and 5 to 10 grams), which has the lowest loss rate. Also, when the A. stellatus fry were placed in different salinities, they had a lower percentage of losses than the other days 65 and 70 (0.5 to 1 and 1 to 3 grams). The highest percentage of losses was related to breeding periods of 55 and 69 days (1.5 to 1 and 1 to 3 grams). The highest percentage of casualties in high salinities (4-9 and 9-13) was related to the age group (1.5 to 1 and 1 to 3 grams). The results of the present research showed that the best breeding period for releasing fish fry out into the sea (salinity 9-13 grams per thousand) was during 77 and 85 days (3 to 5 and 5 to 10 grams) with the lowest loss rate.
Keywords: Tasamahi baby, A. stellatus, Labshor water, Caspian Sea, Release weight, Loss rate