Evaluation of polyculture of chinese carps in periphyton-based ponds

Objective: Pond production systems in southern Asian countries are becoming increasingly reliant on external resources (feed, fertilizers) to supplement or stimulate autochthonous food production for pond fish. Trials have demonstrated that fish production from ponds with substrates for periphyton is higher than that from substrate –free controls. So as a first step in assessing the viability of peripyhton-based fish production in Iran, the effects of phragmites substrate on development of periphyton and on water quality were evaluated. As the second step production of three Chinese carps, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, Cyprinus carpio were compared. Method & Materials: Experiment was carried out in three earthen ponds (23 × 18 m, mean water depth 1m), at Shahid Rajaie Aquaculture Center- Sari, for a period of 60 days. Three treatments were tried: no substrate (control), phragmites submerged substrate equal to 35٪ (S35) and 60٪ (S60) of the pond surface area. Phragmites poles were used as substrate for periphyton and were planted vertically into the pond bottom. After pond preparation, common carp (2-5 gr), silver carp (4-6 gr) and bighead (2-5 gr) were stocked at the ratio of 35: 50: 15, respectively. Results & Conclusion: Water temperature ranged between 23 and 30 c. The average dissolved oxygen concentrations were high in all treatments and never fell below critical level. Some water quality parameters, secchi disc depth, orthophosphate, total alkalinity, ammonia, chlorophyll a were higher in control treatment than in substrate treatment. Periphyton dry biomass, dry matter and ash free dry matter, were 6.3, 4.3, 3.5, 2.2 mg.cm-2, respectively. Net fish yield of bighead and silver carp were higher in substrate treatments, but the yield of common carp did not vary among control and two substrate treatments. Individual weight gains of bighead (18 and 60gr) was higher than silver carp (11 and 26 gr) in two substrate treatments and highest in S60. Net yield of bighead and silver carp was 1.14 and 1.46 times in treatment S35 and 1.32 and 2 times higher in treatment S60. The combined net yield of bighead and silver carp after 60 days were 300, 1034 and 409, 1204.5 kg.ha-1 in ponds with substrate poles and 204.5, 909.9 kg.ha-1 in control pond, an overall increase of 14 and 31.36٪

کلیدواژه ها:

Periphyton ، polyculture ، Chinese carp ، bighead carp ، silver carp