Feeding behavior and the effect of photoperiod on the performance and hematological parameters of the pacamã catfish (Lophiosilurus alexandri)

- Fish learned to use the feeder for self-feeding.
- Fish had strictly nocturnal behavior.
- Fish were able to synchronize feeding with the light period.
- Food intake was higher for fish kept under a 24L regime.
- Cortisol showed high levels in fish subjected to a long period of light.

The aim of this study was to evaluate the rhythms of feeding and locomotor activity, the ability to synchronize to a fixed feeding time, and the influence of photoperiod on the growth parameters, feed intake and hematological parameters of a recently introduced fish in freshwater Brazilian aquaculture, Lophiosilurus alexandri. In experiment 1, six aquariums (60 fish each) had automatic feeders connected to a photoelectric cell set to 12L:12D conditions. The photoelectric cell emitted a continuous beam of infrared light, and the fish used the feeder for self-feeding for 36 days. In the second stage, to evaluate the ability to synchronize animals to food in a 12L:12D photoperiod condition, two different feeding schedules were established (12:00 h and 00:00 h) in a separate aquarium. All data were recorded on a computer. In experiment 2, 160 juveniles, (4.20 ± 0.05 g), were subjected to four treatments: 24 h of light, T1 (24L:0D); 12 h of light and 12 h of dark with food provided during the day period, T2 (12L:12Da); 12 h light and 12 h dark with food provided during the night period, T3 (12L:12Db); and 24 h dark, T4 (24D). The fish feeding was conducted using automatic feeders at fixed feeding times. The growth data calculated were weight gain, length gain, specific weight gain, feed conversion and survival. The blood parameters collected were total protein, hematocrit, glucose and cortisol. Fish kept at a photoperiod of 12L:12D showed greater locomotion (90% of total actions) and feeding activity (88% of total actions) in the dark phase. The locomotion activity was synchronized with the different times of feeding, with a peak of 160 actions at 12:00 h (light phase) and a peak of 180 actions at 00:00 h (dark phase). There was no difference for performance and survival. The feeding intake was improved in fish feed in 24 light condition (T1). The glucose, total protein and hematocrit showed no significant differences. Cortisol was significantly higher in T1 (mean ± SE, 40 ± 2.08 ng mL−1) compared with the other treatments. In conclusion, considering the fish preference and their welfare, we suggest that they should be fed at night although they have the plasticity to adapt to other feeding schedules.