Sources of fish and prawn growth in polyculture ponds as indicated by δC analysis

Abstract

Concentration ratios of naturally occurring stable carbon isotopes, 13C: 12C (reported as δC), were measured in the natural foods and supplied feeds of fish ponds receiving high rates of chicken manure or high rates of fish meal-enriched feed pellets. These δC values, when compared with the body δC of target animals grown in these ponds, indicated the source of feed used for growth. Half the common carp growth was based on natural foods found on the pond bottom and banks even in the presence of a full ration of enriched feed pellets. Tilapia hybrids strongly favored natural foods of photosynthetic origin in preference to either manure-related or feed pellet-related foods. Silver carp body δC matched the δC of microalgae centrifuged from pond water which had been passed through a 37 μm screen. Macrobrachium rosenbergii prawn δC was unchanged for the two manure-feed strategies indicating a feeding pattern independent of the presence or absence of a supplied feed pellet. Prawn δC showed a feeding dependence on natural foods found both on the pond bottom and bank. Chironomids found only on secluded rock surfaces had a δC similar to that of the microalgae.