Uptake of nitrogen from natural food into fish in differently managed polyculture ponds using 15N as tracer

Abstract

Food security in Asia depends significantly on small-scale pond aquaculture in which fish feed on external feeds and natural food resources. Little is known about the assimilation of natural food resources into fish. In order to elucidate the food web and nitrogen flows in a traditionally and a semi-intensively managed pond in Vietnam, d 13 C and d 15 N in pond inputs and fish were measured before and after the application of inorganic 15 N at 1.1 and 0.4 % of total nitrogen. The applied 15 N was traced through the biomass of stocked fish over 30 days. Under traditional management, grass carp was the dominant species in number and biomass. After 30 days, grass carp assimilated 1.2 % of the applied tracer through natural food resources. Filter feeders assimilated only 0.1-0.3 % of the tracer after 30 days because of the limited productivity in the traditionally managed pond. Nile tilapia showed the highest uptake rates over the 30 days, which demonstrated their ability to feed on a variety of natural food resources. In total, 2.6 % of the applied 15 N was assimilated into fish biomass after 30 days. Under semi-intensive management, common carp was the main species numerically and assimilated 1.8 % of the tracer after 30 days. Grass carp was stocked at lower density, but had the highest biomass by the time of the experiment. Grass carp assimilated 0.2 % of the applied tracer suggesting a low contribution of natural food resources to its nutrition. Silver carp benefited most from the higher natural food resources. In total, 4.1 % of applied 15 N was assimilated into fish biomass after 30 days. Traditional small-scale aquaculture of a grass carp-dominated polyculture has a lower assimilation efficiency of applied fertilizers into fish biomass than a common carp-dominated polyculture under semi-intensive management.

Feeding fish or pond . . .?

“…The reduced inclusion of CP in the diet has been complemented by the natural food of the pond. Several studies on different fish species cultured in the pond supported this outcome (Asaduzzaman et al, 2010a(Asaduzzaman et al, , 2010bBombeo-Tuburan et al, 1993;Jackson et al, 2013;Porchas-cornejo et al, 2012;Pucher and Focken, 2017;. The proximate composition of formulated feed affects fish body composition.…”

“…The current study was conducted in outdoor ponds. In outdoor ponds fish have access to natural food in addition to the formulated feed which can stimulate the fish performance (Porchas-Cornejo et al, 2012;Pucher and Focken, 2017;Roy et al, 2012). Algae, that are abundant in fish ponds, can be a potential source of EFA for tilapia (Mizambwa, 2017;Patil et al, 2007;Teuling et al, 2017).…”

“…Also, the 30% of non-fed ponds which has not yet been converted to fed ponds can be included under this approach. Several studies indicated that natural food contributes roughly 50% to the fish growth in outdoor pond aquaculture (Anderson et al, 1987;Asaduzzaman et al, 2010;Focken et al, 1998;Pucher and Focken, 2017). Analysis of the applied feeds and fish yield statistics also support such a conclusion.…”

“…Nutritional studies that formed the basis of National Research Council (NRC) recommendation for dietary requirements in fish (NRC 1993;, were mostly done in absence of the natural food. In outdoor ponds, which is the most commonly used farming system in Asia , fish have access to natural foods besides the formulated feed (Porchas-cornejo et al, 2012;Pucher and Focken, 2017;Roy et al, 2012). Therefore, in ponds, not all nutrients required by the culture species need to be provided in the formulated diet, as is the case with cage or flow-through tanks (Verdegem, 2013).…”

Effect of dietary carbohydrate to lipid ratio on performance of Nile tilapia and enhancement of natural food in pond aquaculture

“…The study of Xie et al (2017) was in flow-through tanks, with a daily water exchange of 50% of the tank volume and the fish had no access to natural food. The current study was conducted in outdoor ponds where fish had access to natural food in addition to the formulated feed which can stimulate fish performance (Porchas-Cornejo, Martínez-Porchas, Luis, Ramos-Trujillo, & Barraza, 2012;Pucher & Focken, 2017;Rahman, Nagelkerke, Verdegem, Wahab, & Verreth, 2008;Roy, Allen Davis, & Whitis, 2012). Algae can be a potential source of EFA for tilapia (Mizambwa, 2017;Patil, Källqvist, Olsen, Vogt, & Gislerød, 2007;Teuling, Schrama, Gruppen, & Wierenga, 2017).…”