Investigations on the digestibility and metabolizability of the major nutrients and energy of maize leaves and barnyard grass in grass carp (Ctenopharyngodon idella)

Abstract

In the uplands of northern Vietnam, culture of grass carp contributes significantly to income and household food security of Black Thai farmers. Maize is one of the most important upland crops and barnyard grass is the most important weed in the paddy rice fields. Thus, these are frequently used by small‐scale fish farmers as fish feed. An 8‐week feeding trial was conducted simultaneously in a recirculation and in a respirometric system to determine the digestibility and metabolizability of the nutrients of maize leaves and barnyard grass, to assess their crude protein, lipid and energy conversion and to estimate the energy allocation in grass carp. The following diets were used: diet ‘A’ (reference diet) containing 39% crude protein with 19.8 MJ kg−1 gross energy; diets ‘B’, ‘C’ and ‘D’, which contained the same amount of the reference diet as the control diet, supplemented with a known amount of dried barnyard grass, dried maize leaves or fresh maize leaves, respectively. Five fish were assigned to each treatment in each experimental unit. Reference and test diets were fed to fish and faecal samples were collected and the oxygen consumption was measured in order to set up an energy budget of the fish over the whole experimental period. The weekly development of the body weight was recorded. The body weight gain of the fish fed diet D was significantly higher than that of the group fed diet A, which also in turn was significantly higher than that of fish fed diet B or C. The apparent digestibility coefficients (ADC) of nutrients and gross energy for the different experimental diets in fish kept in the aquaria were, for diets A, B, C and D respectively, 94.1%, 60.9%, 70.5% and 84.7% for protein, 91.3%, 60.7%, 76.8% and 71.8% for lipid; 95.9%, 44.5%, 60.6% and 69.1% for gross energy. The partial ADC of plant leaf ingredients were determined and barnyard grass and dried maize leaves were found to be not only poorly digestible but having negative impact on the digestibility of the reference diet, while fresh maize leaves were well digested. The results of the present study indicated that fresh maize leaves have a good potential to be used as supplement in diets for grass carp.

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

“…Grass carp under traditional pond management showed a d 13 C signature around -25 %, which suggests that maize leaves and mixed weeds are a substantial feed fraction contribution to the assimilation into fish biomass even though about 70 % of palatable leaf material applied to the ponds had a d 13 C lower than -28 %. This suggests a higher utilization of maize leaves and mixed weeds which is in line with the findings of Dongmeza et al (2010) who reported fresh maize leaf material to be suitable as feed for grass carp while banana and cassava leaves contained high levels of antinutrients ) and were therefore assimilated to a lesser extent.…”

The effects of less-expensive plant protein sources replaced with soybean meal in the juvenile diet of grass carp (Ctenopharyngodon idella): growth, nutrient utilization and body composition

“…In the present study, the fiber contents of all experimental diets were lower than the critical value indicated before. However, it is reasonable to suggest that especially the cell wall of the corn meal is not easily broken by the fish, which could thus not make better use of the cell contents (Li 1996;Dongmeza et al 2010). Cell wall composition of high fiber feed ingredients shows that they contain large amounts of arabino-xylans, pectic polysaccharides and some cellulose.…”

Improved Sustainable Aquaculture Systems for Small-Scale Farmers in Northern Vietnam

“…However, not all of the plant materials currently applied have been found to be suitable as feed for the grass carp. Some of the leaves and grasses applied in the study area showed a limited feed value ) and several feeds even turned out to have a negative impact on fish growth (Tuan et al 2007;Dongmeza 2009;Dongmeza et al 2010). Further, the feed base for the non-grass carp species in this pond system is rather limited.…”

“…Within the framework of the Uplands Program, feeding trials were carried out in aquaria and respirometry systems at the University of Hohenheim and in an aquarium system at the Hanoi University of Agriculture. In the experiments at the University of Hohenheim, grass carp were either fed a standard diet (control group), with the standard diet supplemented with dried cassava leaves or weed mixtures Mix of monocotyles and dicotyles usually collected from paddy fields and dykes (e.g., Alternathera sessili, Commelina nudiflora, Cyperus rotundus, Digitaria timorensis, Eclipta prostata, Kyllinga monocephala, Sagitaria sagitifolia, Sporobolus indicus, Urochloa reptans and Wedelia calendulacea) (Dongmeza 2009), with leaves from banana or bamboo (Dongmeza 2009), or with the leaves of maize or barnyard grass (Dongmeza et al 2010). In all these trials, the leaves and weeds used, with the exception of the maize leaves, came from the farmers in Yen Chau.…”

“…In this case, the authors attributed the lower level of growth to the intake of anti-nutrients. Lower growth rates were also observed in grass carp supplemented with either bamboo leaves, barnyard grass or mixed weeds from the paddy fields, as compared to the respective control groups (Dongmeza 2009;Dongmeza et al 2010). Groups of young grass carp (~20 g) fed solely on barnyard or Napier grass showed low fish growth rates and many of the fish died (Tuan et al 2007).…”