Effectiveness of predator control set-up for aquatic pest control in earthen ponds for extensive culture of Penaeus monodon (Fabricius, 1798) / Rene Geraldo Guerrero Ledesma

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The effectiveness of a conventional predator system for tiger prawn ponds consisting of a net barrier and fence interwoven around a modified pond gateway (set-up 1) was compared to an expanded system that directed water-borne pests to a fish compartment (set-up 2). The compartment had two confinement areas holding fifty, 5 g sea bass fingerlings and nineteen, 300-400 g tiger grouper juveniles separated by a fine mesh net gate secured to a sluice structure. Regardless of the set-up employed, after 88 days of culture, three pest categories were identified inside the ponds: prawn predators, opportunistic feeders, and benthic scavengers. Wet biomasses of fish pests were 1.92 kg and 2.12 kg, while that of mangrove snail was 29 kg and 80 kg in setups 1 and 2, respectively. Prawn length-weight frequency from 30% biomass manifested negatively skewed population curves with the highest frequency size range of 111-120 mm: set-up 2 had a smaller skewness value (-10.68) than set-up 1 (-20.64). A significant t-value of -1.39 (p < 0.10; df18 at t90) indicated that prawns raised in set-up 2 were larger than those grown under set-up 1. Finfish pests collected from set-up 2 were fewer than those in set-up 1, consisting predominantly of smaller (81-120mm) Megalops cyprinoides and Tilapia mossambicus: pests with total lengths below 81 mm were presumed to have been eaten by the sea bass and tiger grouper in the fish compartment. In both predator control systems, the period where tiger prawns are most vulnerable to predation pressure was during the first two months of culture, at lengths less than 111 mm and weights below 12.9 g.

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