Suitability of Polychaete Worms (Marphysa Mossambica) as Protein and Lipids Ingredient for the Culture of Tiger Prawn (Penaeus Monodon) in Hapa Nets in Tidal Ponds of Mtwapa Creek
Abstract:
This study presents an evaluation of cultured polychaetes (Marphysa Mosambicca sp.) as a suitable protein and lipid source alternative to freshwater shrimp in the feed formulation of Tiger prawn (Penaeus monodon) Juve niles. The study was conducted over 94-day period using twelve hapa nets of 1m3 each installed in a tidal pond measuring 0.08 ha at Kwetu training centre farm. Each hapa was stocked at a density of 20 juveniles/m3 of P. monodon collected within Mtwapa creek. The initial weight and length were recorded before stocking, averaging at 1.28+0.84 grams and 5.26±0.68 cm. Polychaete worms (Marphysa mossambica) were cultured at Kwetu Training Centre mariculture systems, and used for preparation of formulated feeds. Three polychaete substitution diets were formulated with varying contents of polychaetes as follows; Poly-30%, Poly-35% and Poly-40%. The commercial shrimp meal with no polychaete added (0%) was used as a control diet. The four diets were administered to the ju veniles @3% body weight for the experiments: (Control (poly 0%), Poly-30%, Poly-35% and Poly-40%). Each diet formulation was randomly allocated to three (3) three treatments, with Control (Poly-0) allocated to Hapa net No. 2, No.7 and No.8), Poly-30% to Hapa No.4, No.5 and No.9), Poly-35% (No.10, No.11 and No.12), and Poly-40% (Hapa 1, 3 & 6). The shrimps were acclimatized for four (4) weeks and thereafter, length and weight sampling to monitor growth, conducted fortnightly. Results showed significant differences in growth rate among the treatments/ diets (Weight (g), F=10.23, P<0.05, Specific growth rate SGR, F=11.99, P<0.05, and exposure periods (Weight WG, F=34.17; SGR, F=122.49). The highest weight gain (2.71 g) and SGRs (5.74 % /day) were recorded on Poly 40% and Poly-35% diet treatments, which were significantly higher than both the shrimp meal and poly-30% diets. The Poly-30% diet had a lower SGR (3.50%/day), but weight gain was comparable to the shrimp meal control diet treatments. Limited quantities of cultured polychaetas and drying methodology for the polychaetes limited 100% polychaete substitution. The results of this study provide a basis for the integration of Marphysa mossambica in the formulation of diets for Tiger prawn. Refining culture protocols for Marphysa mossambica require further investigation.
