Adição de sal comum (NaCl) na ração e na água no controle de Ichthyophthirius multifiliis e crescimento de juvenis de jundiá Rhamdia quelen (Heptapteridae)

Abstract

The increasing proliferation of freshwater fish parasites causes concerns to the fish farmers. One of the main diseases in fish culture is the ciliate protozoan Ichhtyophthirius multifiliis, because severe infections of this parasite provoke high mortalities, causing economical losses to the producers. The objective of this study was to verify the efficacy of the common salt (NaCl) in the food and in the water in the control of Ichthyophthirius multifiliis and growth of juvenile silver catfish Rhamdia quelen (Heptapteridae). After the appearance of the first white spots, indicating infection by this parasite, fish were transferred to eighteen 40 l polypropylene boxes and kept for 30 days. The experimental diets were prepared with salt supplementation (1.0, 2.0, 4.0, and 6.0%) in a diet without salt (0.0%). In addition, in another treatment fish were fed with a diet without salt supplementation and exposed to 4 g/l salt in the water. Juveniles were collected at different times for analyses of whole body Na+, K+, and Cl-. Dietary salt supplementation provoked a transitory increase in the whole body Na+, K+ and Cl- of silver catfish juveniles, but a better stabilization of these ionic levels in infected juveniles was observed in specimens exposed to salt in the water. The obtained results allow to conclude that a diet containing 1.0 % salt (31 mmol/kg Na+ and 145 mmol/kg Cl-) using the present formulation increases weight and biomass of juvenile silver catfish in relation to the treatment with 6% of salt in the ration in 30 days, but the highest survival of infected fish was obtained with exposure to salt in the water.