Transport of silver catfish ( Rhamdia quelen) fingerlings at different times, load densities, and temperatures

Abstract

Silver catfish ( Rhamdia quelen) fingerlings (5–10 cm) were caught from a fish culture pond and placed in a tank for stomach emptying for 24 h. Fingerlings were then weighed and placed in plastic bags (5 l) with 1.5 l water and oxygen, which were kept at temperatures of 15, 20, and 25 °C. The load densities tested were 50, 67, 87, and 168 g l −1. When bags were opened after 6, 12, or 24 h, mortality, dissolved oxygen, pH, total ammonia, non-ionized ammonia, total hardness, nitrite, total alkalinity, and carbon dioxide levels were determined. There was fingerling mortality only at the load density of 168 g l −1 after 24 h of transport at 20 and 25 °C, suggesting that mortality increased with temperature and time of transport. The dissolved oxygen levels in the water were reduced throughout 24 h of transport in the load density of 168 g l −1 at 20 and 25 °C, but remained unchanged at the other load densities. The pH decreased significantly at all load densities and temperatures throughout 24 h. Total alkalinity, total ammonia, and carbon dioxide levels increased significantly up to 24 h of transport in all treatments. Non-ionized ammonia and nitrite levels were below 0.02 and 0.06 mg l −1, respectively. Total hardness ranged from 20 to 48 mg l −1 CaCO 3. The best temperature for transporting fingerlings of this species in plastic bags is 15 °C, because up to 24 h there was no significant mortality even at the load density of 168 g l −1, dissolved oxygen levels were still high, and total ammonia and carbon dioxide presented the lowest increase. Transport at 25 °C and a load density of 168 g l −1 must not exceed 6 h due to the high levels of ammonia and carbon dioxide and low dissolved oxygen levels in the water.