Received: 25-06-2019 / Accepted: 13-08-2019
This study was carried out to examine the effects of different stimulation methods on spawning of the black apple snails, Pila polita. The experiments were arranged in 1 m3 tanks (1×1×1 m) at density of 15 pairs of broodstock snail/tankwhere water column at the beginning was 40 cm high. Experiment 1was done with 4 different water exchanging regimes: 1) Discard 25% water (D25); 2) Discard 50% water (D50); 3) Discard 75% water (D75) and 4) Discard 100% water (D100). Results showed that the highest spawning rate occurred at D75 (60.6%), following by the D50 (58.3%) and these were significantly different from D25 or D100 (P <0.05). The broodstock snails at D75 released highest egg clutches and reproductive efficiency (9.08 clutch/m2; 3.03 clutch/day/m2) and statistically significant different from D25 and D100 (P<0.05). Experiment 2 was implemented in the same condition as the early one (started with 40 cm of water level in the experiemental tanks) but with 4 different spawning stimulation methods: 1) Adding 25% water (A25); 2) Adding 50% water (A50); 3) Adding 75% water (A75) and 4) Addiing 100% water (A100). The spawning rate in A50 (82.2%) was significantly higher (P <0.05) than that inA25 (66.7%) and A100 (64.4%). The numbers of released egg clutches and reproductive efficiency of the snails in A50 (12.3 clutch/m2; 4.11 clutch/day/m2) were significantly higher than those (P<0.05) from A25 (10.1 clutch/ m2; 3.33 clutch/day/m2) or A100 (9.7 clutch/m2; 3.22 clutch/day/m2). The research results show that the spawning stimulation by renewing 75% of water or adding 50% of water volume gave the higher reproductive efficiency than other methods.