Viability of the biological control of the snail Pomacea canaliculata (Lamarck 1822), by Cará Geophagus brasiliensis (Quoy & Gaimard 1824) under the influence of temperature
Author: Ariany Rabello da Silva (Currículo Lattes)
Supervisor: Dr Mario Roberto Chim Figueiredo
In the extreme south of Brazil, rice is cultivated by flooding the crop. The technology of planting pre-germinated rice has increased the occurrence of pests such as snails Pomacea canaliculata, and its main natural predator, the hawk-eagle Rosthramus sociabilis, has been insufficient for control. An alternative would be the consortium between rice and fish, using the Cará Geophagus brasiliensis for the biological control of the pest. In step I of the experiment, the objective was to evaluate the predation of P. canaliculata by G. brasiliensis at different water temperatures (18, 22, 26, 30 and 34ºC), and in step II, to evaluate the predation in different size classes of the snail (shells up to 3 mm; 3 - 5 mm; 6 - 8 mm; 9 - 11 mm and 12 - 14 mm), with water at a temperature of 26°C. 15 fiber cement tanks (45 L) were used,in a completely randomized design, with three repetitions. The snails (n = 32 per tank) were offered to juvenile cards (n = 4 per tank) for 18 h, counting the remaining snails. The predation index (PI) was calculated by the relationship between predated individuals and individuals offered to fish. In step I the snails (up to 3 mm) were distributed to the Carás in tanks with water at the referred temperatures. Between the temperatures of 18 and 22ºC there was a significant difference in the predation index (IP), the same occurring between 22 and 26°C. However, the PI did not vary significantly between temperatures 26, 30 and 34ºC. The proximal composition of the snails was analyzed as they were found in the cultivated water (SL) and previously washed (CL), verifying that they are rich in ash (approx. 70%),they have low fat content (the material adhered to the shell more fat than the snail: SL = 3.17 against CL = 0.97%). In step II, the oral diameter of the Carás (n = 23) was measured and the correlations between this value (mean 10.36 ± 1.33 mm), the biometric data of the fish (live weight, total length) and the PI were calculated, verifying that the buccal diameter increases with the growth of the fish and that this factor limits the size of the predated snails (shells <10 mm in this experiment). It was concluded that the Carás efficiently prey on snails at temperatures above 26°C, very close to the water temperature in the rice field at the time of planting, and that these fish are efficient predators of this gastropod in the initial size classes.