Effects of Organic and Chemical Fertilizers and Biological Control of Problem Organisms on Production of Fingerling Striped Bass, Morone saxatilis

Abstract

Sixteen 0.04-ha ponds were fertilized with similar amounts of nitrogen (N) and available phosphorus (P) provided by either alfalfa meal, urea and phosphoric acid, or a combination where half of the P was provided by phosphoric acid and half by alfalfa meal. Half of the ponds fertilized with the combition of nutrients were stocked with adult male common carp, Cyprim carpio, at an average biomass of 168 kg/ha to provide biological control of rooted aquatic plants and clam shrimp, Cyzicus morsie. All ponds were stocked with 25,000 larval striped bass, Morone saxatilis, at an age of D4 (Dl is the day of hatch). Median harvest density and survival were about 100,000ha and 16%. Number harvested was directly related to numbers sampled with a light and dip net at D5 and D8. Low survival was probably related to high afternoon water temperatures (25-26°C) and relatively low morning dissolved oxygen (4.6-6.5 mg/L) when larvae were D5. Stocking larvae at an age prior to swim bladder inflation resulted in an inflation success of 99%. Dynamics of average net photosynthesis, chlorophylla concentrations, and densities of crustacean zooplankton, as well as mean number, biomass, and length of fingerlings harvested were similar in all treatments, regardless of whether the source of P was organic, inorganic, or the combination. Growth rate of larvae from DS to D8 was considered satisfactory (≥0.4 mm/day) with average densities of crustacean zooplankton of 10-20/L. The average growth rate of larvae from D8 to D40 was negatively related to number harvested. A weekly fertilization rate of available P from 28-38 µg/L resulted in satisfactory average growth rate (0.83 mm/day) of decreasing numbers of larvae at increasing ages: D8-D19-150.000ha. D19-D25-125.000/ha, and D25-D40-73,000/ha The presence of adult common carp provided several benefits: effective control of Chara and filamentous algae; a lower average percentage of fingerlings stranded in vegetation when ponds were drained (0.4% vs 10.1%); lower pH; effective control of clam shrimp.