Comparisons of tilapia seed production under various broodstock densities and fry stocking densities

Four methods of seed (eggs, sac-fry, and fry) production for Rocky Mt. White hybrid® tilapia, (0. niloticus x O. aureus), were compared under green water conditions over a six month period in an environmentally controlled greenhouse at the Virginia Polytechnic Institute and State University's Aquaculture Research Laboratory. Twelve 3 m2 rectangular tanks were stocked with brood stock (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 m-2), and seed was collected from females' mouths weekly. Three additional tanks were stocked at a density of 2 females m-2, and fry were collected from the edges of the tanks when seen.

Seed production was among the highest seen for related studies. Average number of viable fry produced at I females m-2, 1660 fry female- I month-I, was significantly higher than the combined average production of densities 2 females m-2 (629 fry female- I month-I) and 4 females m-2 (695 fry female-1 month- 1) (p< 0.02). Even though there was no significant difference between viable fry production meter-2 (p>0.05), the highest density consistently produced more fry meter-2. No significant difference was observed in viable fry production between the two seed collection methods (Clutch removal- 629 fry female-1 month-I; Natural mouth-brooding- 520 fry female-1 month-I) (p>0.05).

The effects of stocking density on growth and survival were evaluated by stocking 14-16 day old artificially incubated fry (25.5 ± .32 mg, 12.1 ± .04 mm), into 150 liter troughs at three densities (3, 6, and 12 fry liter-I) under green water conditions for 30 days. The mean monthly hatchery seed survival was 65.7 ± 2.3%, which varied largely depending on initial seed developmental stage. Significant differences were observed between mean weight, length, survival, and feed conversion ratios among the various fry stocking densities (p<O.05). The greatest growth was at a density of 3 fry liter 1 , while survival was not affected until a density of 12 fry liter-I.

These results that to maximize fry production and reduce labor, a density of 4 females m-2 or higher be used under the natural mouth brooding seed collection method. They also suggest a fry density between 6 to 12 fry liter-1 should be used with periodic grading or sex reversal to reduce cannibalism and increase growth.