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Abstract
The present work was conducted to study the effect of conditioning and exchange on reproduction performance of 0. niloticus broodfish in hapas, on serum levels of sex steroid hormones and total calcium in spawned females in spawning hapas and from conditioning hapas, as well as comparison between production of fry in earthen spawning ponds and hapas and differerrtiate between nursing of fry in earthen ponds and hapas. The experiment was conducted during the spawning season 2008, started on 20 May and continued to 30 August
The results obtained as follow:
1- Ten days conditioning (T1) had the highest fry number (55487) followed by 15 days conditioning, T2 (42314), 20 days conditioning, T3 (40023) and control (no conditioning) (24718) throughout the experimental period.
2- Ten days conditioning (T1) had the highest fry number female’ (4624) followed by
15 days conditioning, T2 (3526), 20 days conditioning, T3 (3335) and control
(2060).
3- Ten days conditioning had the highest total number of fry produced female1 spawn1 (578) followed by 20 days conditioning (417), 15 days conditioning (294) and control (257) during the period of experiment.
4- Ten days conditioning had the highest relative fecundity (33) followed by 15 days conditioning (25), 20 days conditioning (24) and control (15).
5- Ten days conditioning had the highest total number of fry m2 day1 (139) followed by 15 days conditioning (106), 20 days conditioning (100) and control (62).
6- Levels of steroid hormones and total calcium in conditioned females were higher than spawned females
7- Production of fry in hapas was higher than earthen spawning ponds and in comparison of fry number produced per female in hapas and ponds found that female broodfish in hapas gave higher fry number suitable for sex reversal than female brood fish in earthen spawning ponds.
8- Nursing of fry in earthen ponds was better than hapas. Body weight, daily weight gain and specific growth rate in earthen ponds were higher than hapas.
On the basis of these results it can be concluded that
1- Exchange and conditioning techniques in hapa — based systems represented an important method for tilapia hatcheries to increase and maintain seed productivity.
2- Ten days conditioning was the best period for conditioning and increase period of conditioning more than 10 days did not improve seed output.
3- High levels of circulating steroids and total calcium as an indirect measure of hepatic vitellogenin production are indicative of females maintaining good condition and readiness to spawn. Steroid levels explained how brood fish exchange can intensify seed production.
4- Hapa — based systems were better than earthen spawning ponds in fry production especially fry suitable for sex reversal.
5- Nursing of fry in earthen ponds was better than nursing in hapas.