Kentucky State University

Effects of Different Tilapia Oreochromis niloticus Densities on Water Quality in Freshwater Shrimp Macrobrachium rosenbergii Ponds

Institution

Kentucky State University

Abstract

Regional prawn farmers have at times experienced problems with high pH in grow-out ponds due to excessive algal blooms. Nile tilapia are known to graze on phytoplankton and may potentially be used to thin algal blooms. The objective of this study was to determine the effect of two densities of caged tilapia on the water quality of prawn ponds. The experiment lasted 115 days and was conducted in nine 0.04 hectare ponds and consisted of three treatments with three replicates each. Control ponds (CTL) contained only prawns. Low density polyculture (LDP) contained two cages of tilapia and high density polyculture (HDP) contained four cages. All ponds contained circulators and substrate. Each pond was stocked with juvenile prawn (0.9 g) at 69,000/ ha. Tilapia (115 g) were stocked in 1 m3 round cages at 100/m3. Tilapia were fed a 32% protein floating pellet once daily to satiation. Prawn were fed a 32% protein sinking diet twice daily based on a feed chart. Overall means for afternoon pH were significantly lower in polyculture treatments (7.79 mg/L) than control ponds (7.93 mg/L). Nitrite-nitrogen concentrations were significantly higher in polyculture treatments (0.21 mg/L) than in control ponds (0.05 mg/L). Total ammonia-nitrogen concentrations were significantly higher in polyculture treatments (1.00 mg/L) than in control ponds (0.73 mg/L). However, unionized ammonia concentrations did not differ significantly by treatment and averaged 0.60 mg/L overall. The presence of tilapia resulted in lower pH levels likely due to the grazing of phytoplankton. While feeding tilapia resulted in slight increases in total ammonia, the toxic un-ionized form was not increased due to the lower pH.

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Effects of Different Tilapia Oreochromis niloticus Densities on Water Quality in Freshwater Shrimp Macrobrachium rosenbergii Ponds

Regional prawn farmers have at times experienced problems with high pH in grow-out ponds due to excessive algal blooms. Nile tilapia are known to graze on phytoplankton and may potentially be used to thin algal blooms. The objective of this study was to determine the effect of two densities of caged tilapia on the water quality of prawn ponds. The experiment lasted 115 days and was conducted in nine 0.04 hectare ponds and consisted of three treatments with three replicates each. Control ponds (CTL) contained only prawns. Low density polyculture (LDP) contained two cages of tilapia and high density polyculture (HDP) contained four cages. All ponds contained circulators and substrate. Each pond was stocked with juvenile prawn (0.9 g) at 69,000/ ha. Tilapia (115 g) were stocked in 1 m3 round cages at 100/m3. Tilapia were fed a 32% protein floating pellet once daily to satiation. Prawn were fed a 32% protein sinking diet twice daily based on a feed chart. Overall means for afternoon pH were significantly lower in polyculture treatments (7.79 mg/L) than control ponds (7.93 mg/L). Nitrite-nitrogen concentrations were significantly higher in polyculture treatments (0.21 mg/L) than in control ponds (0.05 mg/L). Total ammonia-nitrogen concentrations were significantly higher in polyculture treatments (1.00 mg/L) than in control ponds (0.73 mg/L). However, unionized ammonia concentrations did not differ significantly by treatment and averaged 0.60 mg/L overall. The presence of tilapia resulted in lower pH levels likely due to the grazing of phytoplankton. While feeding tilapia resulted in slight increases in total ammonia, the toxic un-ionized form was not increased due to the lower pH.