Effect of fish on the yield and yield components of rice in integrated concurrent rice–fish systems

Abstract

Many authors report on the effect of rice-fish culture on rice yields. Some reports show increased rice yields, others show no effect or even decreased yields. To verify the impact of rice-fish culture, data gathered over eight experiments (1995)(1996)(1997)(1998)(1999) at the Co Do experimental rice-fish station, Vietnam, were analysed through multiple regressions with rice yield and different yield components as the dependent variables. We used eight independent variables : season, water depth, rice variety, rice seeding rate, and the effective stocking density (ESD) of silver barb, Nile tilapia, common carp and snakeskin gourami. Season had the biggest impact on nearly all dependent variables. Rice yields in the wet season were on average 2n42 t\ha lower as compared to the dry season. Higher water levels decreased the number of panicles\m# and the rice yield. The rice seeding rate affected the yield component variables, but had no impact on the rice yield. Silver barb feeding decreased the number of panicles\m# but this was compensated by an increased number of grains\panicle. Snakeskin gourami had a positive effect on panicles\m# and, together with common carp, on sink capacity, probably through improved nutrient cycling in presence of fish and improved nutrient uptake by the rice plant. Snakeskin gourami had a negative effect on the ripening ability, whereas Nile tilapia had a positive effect. Fish did not have any impact on the rice yield. Increased water level and reduced rice arable area, the main two requirements for rice-fish culture, result in lower rice yields from rice-fish systems as compared to monoculture systems.

Integrated rice-fish culture: Coupled production saves resources

“…Rothuis et al (1999) conducted field experiments in Vietnam and found a slight, although not statistically significant, increase in average rice production after the introduction of three different species of fish, being Nile tilapia, common carp and silver barb. Vromant et al (2002a) summarized the results of eight field experiments carried out in Vietnam, which confirmed that although different fish species had a positive effect on individual aspects of the rice yield -such as the number of panicles/m 2 , the number of grains/panicle, or the number of lateral shoots (tillers) issuing from the base of the stems -they could not confirm a significant impact on the net grain yield. Frei and Becker (2005) cite controversial effects on rice growth, in a controlled greenhouse experiment, depending on which fish species, or combination of species, was present.…”

“…Rothuis et al (1999) have demonstrated that a low seeding rate does not have a negative effect on rice yields. The need to maintain a refuge for the fish, commonly occupying around 10% of the field, reduces the space available for rice cultivation (Vromant et al, 2002a). However, this loss may be compensated by enhanced rice growth.…”

“…Fish, especially bottom feeders such as carp, perturb the upper soil layers during their search for feed, and may thus interfere with methanogenic processes. Various authors assume that fish incorporate oxygen into the soil through their feeding activities Langhu, 1995;Vromant et al, 2002a), which would in turn mitigate methane production. Frei and Becker (in press) have detected a mechanism which acts in the opposite direction: by burrowing into the soil, fish may release methane entrapped in the soil.…”

Effect of fish in rice-fish culture on the rice yield

“…However, it is rare that rice yield in rice-fish culture has been rigorously compared with that in rice monoculture, such as by incorporating statistical tests and equal experimental conditions (see [3,7,9]). Moreover, in all of these studies, the hypothesis was not supported by statistically significant results [12][13][14][15][16][17][18][19][20][21][22][23][24]. Furthermore, the ecological processes leading to higher rice yield in rice-fish culture were not demonstrated (but see [25]).…”

An assessment of fish species assemblages in rice fields in West Bengal, India: implications for management

“…The period of wet conditions in rice fields is also a constraint to growing many fish species to a larger size and the possibility of their breeding. The water depth in the paddy fields is an important determinant in equitable rice and fish production (Vromant et al., 2002). In view of these, fish species that are naturally adapted to these conditions can be a better choice to marginalize the trade‐off of rice and fish production.…”