Use of pig manure as fertilizer with and without supplement feed in pond carp production in Northern Italy

Abstract

A 4-month trial was carried out in Northern Italy to evaluate the possibility of recycling pig manure through pond carp production. Six ponds (600 m 2, 1.2 m deep) were stocked at the rate of 5300 fish/ ha with a mixture of common and grass carp (87% and 13% by number, respectively). The initial mean weight was 450 g (carp) and 440 g (grass carp). Ponds were fertilized with pig manure and/ or supplied with feed (dry matter weight on the basis of fish biomass) as follows: (A) 3% manure; (B) 1.5% manure and 1.5% feed; (C) 3% feed. Dry matter was around 13% (manure) and 88% (feed). Five days a week, manure was spread and/or feed distributed in ponds; every week the supplied amount was adjusted with estimated weight gains. The overall quantity of manure recycled per day was 575 (treatment A) and 288 kg/ha (treatment B). Survival was 100% in treatments B and C, and 88% in A. The total weight gain was different ( P ⩽ 0.05) in each treatment: 259 (A), 3369 (B) and 6312 (C) kg/ha. The final mean weight was 570, 1050 and 1670 g for common and 630,1330 and 1480 g for grass carp in treatments A, B and C, respectively. Feed conversion rate was 2.82 (B) and 1.52 (C), while the fertilization index (kg manure/kg weight gain biomass) was 36.1 for treatment A. The level of oxygen was different ( P ⩽ 0.05) among the treatments, i.e. 3.6 (A) vs. 4.5 (B) and 4.3 (C) mg/l. An over-fertilization effect could have been responsible for poor performances and the high mortality in treatment A. As a general conclusion, integrated pond systems using grass carp seem to be useful for pig manure recycling.