Growth and feeding behavior of fishes in organic rice–fish systems with various species combinations

Abstract

Four combinations of fish and prawn species were stocked in organic rice–fish systems to examine their growth performance, feeding habits, competitive interactions, and food-web structure. The species combinations were: (I) three fish species commonly stocked in rice–fish systems in the Lower Mekong countries, namely Barbonymus gonionotus, Cyprinus carpio, and Oreochromis niloticus; (II) the same three species plus the giant freshwater prawn Macrobrachium rosenbergii; (III) three herbivorous fishes native to the Mekong River, namely B. gonionotus, Barbonymus schwanenfeldii, and Cirrhinus microlepis; and (IV) the herbivorous and omnivorous fishes B. gonionotus, C. microlepis, and Trichogaster pectoralis, together with the carnivorous fish Channa striata. Growth performance was examined using specific growth rate (SGR), and feeding habit was examined through stomach content and stable isotope (carbon and nitrogen) analyses. All fish and prawn species exhibited SGRs of roughly 1–2% d−1 except for C. striata, which had a slower growth rate (<1% d−1). Various food items were identified in the fish diets, including phytoplankton, zooplankton, benthic algae, and insects. Despite some dietary overlap, a comparison of indices of relative importance clearly indicated that foods were consumed at different proportions by different species within each species combination. The stable isotope analysis also revealed various degrees of trophic niche partitioning among species. The standard ellipse areas of isotopic niches showed higher feeding plasticity in many of the herbivorous and omnivorous fishes than in the prawn or the carnivorous fish C. striata.