Separated breeding of perch fingerlings (Perca fluviatilis L.) with and without initial inflated swim bladder:: comparison of swim bladder development, skeleton conformation and growth performances

Perch juveniles with (S+) and without (S-) functional swim bladders were separately bred, under similar conditions, from Days 30 to 105 post hatch. Sixty-six percent (+/-7%) of uninflated swim bladder fishes were found to inflate their swim bladders during this period. Late-inflated swim bladder fingerlings (S+/-) presented diverse swim bladder morphology; their size increased during the study period, but they remained smaller than early-inflated swim bladders. First lordosis appeared on S- fingerlings from Day 48. Twenty-five percent of S+ fingerlings also presented lordosis, but none was noted in S+ individuals. The lordosis angle increased quicker in S- than S+/- juveniles; on Day 105, it respectively reached 37.9 +/- 2.6degrees and 29.9 +/- 4.2degrees. S- fingerlings expressed the lowest growth performances: 65.2 +/- 1.7 mm. S+ juveniles have recovered their growth lately (72.9 +/- 1.4 mm), reaching a final length close to those of S+ juveniles: 68 +/- 1.6 mm. Beyond Day 30 post hatch, the separate rearing of fingerlings with and without swim bladders can have a commercial interest as it allows half the fish without swim bladder to lately inflate and to follow a normal development and finally contribute to increase hatchery performances. (C) 2004 Elsevier B.V. All rights reserved.