Organic and Mixed Organic–Inorganic Fertilization of Plastic‐Lined Ponds for Fingerling Walleye Culture

Abstract

Treatment with organic fertilizer was compared with treatment involving a mix of organic and inorganic fertilizers for culture of walleye Stizostedion vitreum fingerlings in 0.04-ha plastic-lined ponds. Organic fertilization consisted of weekly additions of alfalfa and cottonseed pellets. Each type of organic fertilizer was applied to each pond at 2.3 kg/week. Nitrogen (36-0-0 as N-P-K) and phosphorus (12-49-6) fertilizers were used weekly to adjust the ratio of nitratenitrogen to total phosphorus ratios in the mixed-fertilizer treatment to 7:1. Nutrient values in ponds treated with organic fertilizer were similar to those in ponds treated with the organic-inorganic mix. However, the water used to fill the ponds was initially high in both nitrogen and phosphorus, which may have reduced the nutrient differences between treatments. There were also no differences in food base densities (zooplankton and benthos) or fingerling production between treatments. Concentrations of dissolved oxygen at pond bottoms were sometimes less than 1 mg/L in the morning in both treatments; however, this had no apparent effect on fingerling survival in either treatment. Daphnia spp. and copepod populations sharply declined in both treatments after fish were stocked, suggesting that larval walleyes immediately fed on these crustaceans. Zooplankton populations remained low until near the end of the season. Benthic invertebrate densities were high throughout the season in both treatments and showed no differences between treatments. Stomach content analyses revealed walleye fingerlings consumed Daphnia spp. and copepods throughout the experiment, whereas dipteran larvae became increasingly important once walleyes reached 20 mm, about 2 weeks into the experiment. Both fertilization treatments produced relatively large fish (0.57 g) with good survival rates (Ͼ50%). The results from this study suggest that dipteran management is important for providing food items for larval walleyes and that high initial nutrient levels from water sources may reduce the requirements for inorganic enrichment in plasticlined ponds for walleye culture.

Origin of Chironomid Larvae in Plastic‐Lined Culture Ponds: Airborne or Water Supply?

“…These findings show that in the absence of a ready source of chironomids, such as nearby water resources, there may be varying culture success of fish that depend on aquatic macroinvertebrates during the culture season (e.g., walleyes; Rogge et al 2003), especially when the fish are reared in plastic-lined ponds. Improvements that could be adopted in future, similar studies include greater replication and use of smaller-mesh filters to limit chironomid eggs in the incoming water.…”

“…In earthen production ponds, the determination of macroinvertebrate origin and their subsequent management are not critical because invertebrates are able to live and survive between culture seasons in bottom sediments. However, chironomid populations in plastic-lined ponds are more problematic (Rogge et al 2003).…”

“…Benthic invertebrates, notably chironomids, become essential to the diet of walleye fingerlings towards the end of their initial culture phase, especially when managed cladoceran populations become limited by excessive predation by older fingerlings (Rogge et al 2003).…”

A Benthic Sampler for Plastic‐lined Ponds

“…To address this concern, Rogge et al (2003) used Hester–Dendy (Hester and Dendy 1962) multiple‐plate samplers to estimate benthic invertebrate populations in the newly constructed plastic‐lined ponds at Rathbun Fish Culture Research Facility, Moravia, Iowa. In a follow‐up study at Rathbun Hatchery, Kaatz (2003) investigates benthic invertebrate fauna by using adult emergent traps as well as these same multiple‐plate samplers.…”

“…Proper pond management requires that fish culturists have an understanding of the relationship between key benthic populations, stocked fish fry, and the time needed to develop suitable prey populations to maximize fish survival. For instance, Rogge et al (2003) found that larval walleye fry will start consuming chironomid larvae at 10-14 d posthatch.…”