Can the polyculture with South American catfish improve the feeding efficiency of rainbow trout culture?
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The objective of this study was to determine if the South American catfish (Rhamdia quelen) is suitable to be farmed in polyculture with rainbow trout (Oncorhynchus mykiss) in intensive systems during the juvenile phase to maximize feed efficiency. Juveniles of rainbow trout (3.94 ± 0.11 g) and South American catfish (2.07 ± 0.04 g) were distributed in 16 tanks (100 L) with continuous water renewal at the density of 50 fish/tank. The experimental design was completely randomized with four treatments (proportions between species) and four replicates. The treatments were 100% trout (100T), 70% trout and 30% catfish (70T30C), 50% trout and 50% catfish (50T50C), and 100% catfish (100C). Fish were fed twice daily with pelleted commercial feed (45% crude protein) during an experimental period of 56 days. No feed was provided for the catfish in polyculture. The weight gained by the trout was higher in polyculture. Fish survival did not differ among the treatments. The average survival of the trout in all tanks was 99.6 ± 1.0%, while the survival of the South American catfish was 97.9 ± 2.7%. The total feed conversion ratio was lower in the 70T30J treatment, followed by the 100T treatment. Rainbow trout and South American catfish are compatible species for farming together in the first phase of their juvenile development. The different spaces occupied by these species inside tanks probably prevent competition or agonistic behavior. Catfish eat the non-ingested leftover diet from the trout, which improves feed conversion and increases sustainability.