Growth, Condition, and Size Distribution of Paddlefish, Polyodon spathula, Juveniles Reared in Ponds at Three Densities

A study was conducted to determine the effect of increasing density on growth and size distribution of paddlefish, Polyodon spathula, juveniles reared in ponds. Feed-trained paddlefish of mean weight (±SE) 25.8 ± 1.1 g were randomly stocked into nine 0.02-ha ponds at 12,355, 18,533, and 24,710 paddlefish/ha, three replications per treatment. The fish were fed daily in excess of what they would eat for 97 d, beginning with a floating trout diet containing 45% protein and 16% lipid and then transferring to a floating catfish diet containing 32% protein and 4.5% lipid. Survival at harvest was not significantly different (P > 0.05) among treatments and averaged 90%. Mean final weights (±SD) for the low-, middle-, and high-density treatments were 205.2 ± 54.1, 174.8 ± 53.2, and 178.6 ± 51.4 g, respectively. Best-fit distributions centered on these means were lognormal. The low-density distribution was significantly different (P < 0.05) from the two higher densities, which were not significantly different from each other (P > 0.05). Paddlefish weight at the minimum target length of 35 cm was estimated to be 100 g by regression analysis. The probability of paddlefish reaching or exceeding 100 g was 90% for the low-density treatment. For the two higher densities, probabilities were 79 and 78%, respectively. Mean Fulton's condition factors (FCFs) (±SD) were 250 ± 19, 242 ± 4, and 256 ± 37 for the low-, middle-, and high-density treatments, respectively. The FCF for the middle-density treatment was significantly lower than for the low- and high-density treatments (P < 0.05), which were not significantly different from each other (P > 0.05). CV, feed conversion ratio, and relative growth were not significantly different (P > 0.05) among treatments and averaged 0.43, 1.50, and 5.45, respectively. Monoculture of paddlefish juveniles in ponds results in a hierarchic size structure when density is at least greater than 12,355 paddlefish/ha. The effect is enhanced with increasing density but becomes asymptotic as density approaches 18,533 paddlefish/ha. Feeding in excess does not ameliorate the effect.