Fasting/re-feeding and water temperature promote the mobilization of body reserves in juvenile freshwater carnivorous catfish Lophiosilurus alexandri

Abstract

We investigated the effects of water temperature and fasting on physiological and metabolic parameters of juvenile pacamã (Lophiosilurus alexandri). Fish subjected to fasting for 15 days followed by re-feeding for five days in two water temperatures (28 and 24 °C) were sampled after fasting and after re-feeding and compared to fish that did not experience fasting under the same temperatures. Glucose and triglyceride levels decreased during fasting for fish at both water temperatures (P < .05). Plasma cholesterol decreased during fasting for the fish submitted to 24 °C. Both plasma glucose and cholesterol remained low for fish submitted to 24 °C. There was an increase in liver lipid levels and a decrease in the hepatosomatic index (HSI) (P < .05) for fasted fish at both temperatures. However, liver lipid levels returned to the level of the respective fed fish after re-feeding while the HSI of fasted fish remained lower after re-feeding compared to the continually fed fish. Hemoglobin and hematocrit increased in fasting fish at 24 °C; after re-feeding both parameters remained at high values (P < .05). In conclusion, different water temperatures and fasting promoted the mobilization of body reserves in juvenile L. alexandri, and caused changes to hematological variables. Re-feeding for five days was not sufficient for the recovery of these body reserves and the hematological variables, especially for the fish submitted to the lower water temperature of 24 °C.