Comparisons of Tilapia Seed Production Under Various Broodstock Densities and Fry Stocking Densities.
Three types of seed (eggs, sac-fry, and fry) production for Rocky Mountain WhiteŽ hybrid tilapia, (O. niloticus x O. aureus), were compared under green water conditions over a six-month period in an environmentally-controlled greenhouse at the Virginia Tech Aquaculture Center. Rectangular tanks were stocked with broodstock (mean wt. 680 g), at a sex ratio of 3 females to 1 male. Nine tanks were stocked at one of three densities (1, 2, and 4 females/m2), and seed was collected from the females' mouths weekly. Three additional tanks were stocked at a density of 2 females/m2, and fry were collected from the edges of the tanks daily.
Average number of viable fry produced by the clutch removal method at 1 female/m2 was significantly higher than the combined average production of densities at 2 and 4 females/m2 (p< 0.02). Even though there was no significant difference between viable fry production per meter sq. (p>0.05), the highest density consistently produced more fry/m2. No significant difference was observed in viable fry production between the clutch removal method and the natural mouth-brooding method (p>0.05). The mean monthly hatchery seed survival was 65.7 + 2.3%, which varied largely depending on initial seed developmental stage.
The effects of stocking density on growth and survival were evaluated by stocking 14-16 day old artificially incubated fry (25.5 + 0.32 mg, 12.1 + 0.04 mm), into 150-liter troughs at three densities (3, 6, and 12 fry/liter) under green water conditions for 30 days.
Significant differences were observed between mean weight, length, survival, and feed conversion ratios among the various fry stocking densities (p<0.05). The greatest growth was at a density of 3 fry/liter, while survival was not affected until a density of 12 fry/liter was reached.
These results suggest that to maximize fry production and reduce labor, a density of 4 females/m2 or higher be used under the natural mouth-brooding seed collection method. They also suggest a fry stocking density between 6 to 12 fry/liter should be used with periodic grading or sex reversal to reduce cannibalism and increase growth.