Mass, volume, and length relationships in plaice (Pleuronectes platessa L.) juveniles

The live body mass, body volume, and length were determined for four groups of juvenile plaice (Pleuronectes platessa L.): (1) plaice immigrating into the Wadden Sea, (2) fish that had settled in the Wadden Sea, (3) settled fish that had been starved, and (4) laboratory-reared fish. Mass and volume values were obtained by applying Archimedes' principle to weights of fish obtained while they were immersed in waters of different densities. The allometric relationship of mass, volume, and length was determined for each group using principal component analysis. Fish in each treatment group had different mass-volume-length trajectories. Immigrating fish had the least mass and volume at fixed length, followed by settled fish, and laboratory-reared fish had the greatest mass at fixed length. Mass and volume differences between freshly captured settled fish and starved fish were slight. All treatments showed great variability in body mass and volume at fixed length, and the use of fish length alone as an index of fish size is problematic. It is suggested that centroid size is a better measurement of fish size when size is an important variate in a study.