Browsing by Subject "Fischfutter"

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    Effects of low dietary levels of saponins on two common culture fish - common carp (Cyprinus carpio L.) and Nile tilapia (Oreochromis niloticus (L.))
    (2001) Francis, George; Becker, Klaus
    Saponins are a group of compounds present in many wild plants and cultivated crops and are commonly found in traditional medicinal preparations. Feeding experiments using saponin-supplemented (commercial Quillaja saponin) feeds were conducted in two commonly cultured fish species, namely common carp (Cyprinus carpio L.) and tilapia (Oreochromis niloticus (L.)). Quillaja saponins (QS) at dietary levels of 150 mg kg-1 and 300 mg kg-1 significantly increased body weight gain in common carp and Nile tilapia compared to controls. When fed to tilapia fry QS (700 mg kg-1) altered the normal 1:1 sex ratio. In separate, in vitro measurements it was found that QS stimulated the release of leutinising hormone (LH) from cultured tilapia pituitary cells, but apparently this did not happen in vivo since serum levels of LH were not found to be elevated in the saponin fed fish. Dietary saponins were also found to affect serum and muscle cholesterol levels. Adult tilapia - but not tilapia fry - fed a dietary level of 300 mg kg-1 QS were found to have significantly higher muscle cholesterol levels than fish fed the control diet. In tilapia fry, the average serum cholesterol levels in males showed a steady increase from dietary QS levels of 0 to 700 mg kg-1, while no such trend existed among the females. Supplementation with 50 and 100 mg kg-1 of Yucca schidigera butanol extract (containing steroidal saponins) did not significantly promote the growth of carp despite showing initial promise. The purified haemolytic fraction of triterpenoid Gypsophila saponin extract (isolated using column chromatography) did not produce any toxic effects in carp at dietary levels up to 250 mg kg-1 in a preliminary feeding trial. A growth promoting effect was however evident at the very low level of about 5 mg kg-1 when the purified fraction was used. More research needs to be done to determine the mechanisms of action of QS and to test whether saponins from other sources have similar effects.
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    Studies on the nutritional quality of plant materials used as fish feed in Northern Vietnam
    (2009) Dongmeza, Euloge Brice; Becker, Klaus
    Fish demand has risen worldwide as populations have grown and incomes have increased; thus, fish are highly likely to continue becoming more expensive over the next two decades. This situation could endanger the availability of fish to the lower income groups and poor people in developing countries. Fisheries and aquatic products are an important source of protein in Vietnamese diets. However, in the upland areas, fish is scarce and expensive, and signs of protein malnutrition such as discoloration of hair and skin could be frequently observed among the poor inhabitants of Son La province, Northern Vietnam where the average price for fish on the local market was approximately 1.4 US$ kg-1 in 2005 which can be considered high, particularly when compared to the monthly per capita income in Son La of approximately 13.4 US$. Nevertheless, in the villages of that region nearly all households have at least one pond. The major inputs to the ponds system are crop leaves and residues and occasionally grasses and weeds. The annual fish production is low in the region. The aquaculture system in this region is lacking in adequate feed and feeding concept for the different fish species kept here. Fish are cultured in tilapia and cyprinid-based polyculture, the main species being grass carp which is the only species capable of efficiently ingesting and digesting the soluble cell contents of the leaf material used as input to the pond system. Despite these constraints, fish farming contributes enormously to food security in the region and generates incomes. Up to now, none of the feeds currently used in Son La Province have been analysed or tested. Therefore in the first part of this study presents a quantitative evaluation of the gross chemical composition, energy and antinutrient content of the plant residues used as fish feed in the course of the year in Son La Province, Northern Vietnam. The potential of some of these plant materials (such as Banana, cassava and bamboo leaves) to be used all over the year as fish feed depending on the seasonal variation of their nutrient, energy and antinutrient compositions has been presented. In this study, the analysis of the different feedstuffs fed to fish in northern Vietnam showed that some of them had relatively high protein and low fibre content. However, for some of the feedstuffs the antinutrient content was high. During the second part of this work, feeding experiments were conducted simultaneously in a computer controlled respirometer system, which allowed feeding and continuous measurement of oxygen consumption and in a water recirculation aquaria system where the faeces collection was more viable and the apparent digestibility and metabolisibility of the nutrients and energy of six of these plant residues in grass carp have been determined. The simultaneous measurement of the oxygen consumption of the fish fed the diets containing the different plant leaf materials gave accurate informations on the metabolic cost (amount of O2 consumed per unit of body mass gain) of the utilization of the diets containing these plant leaves. The results of the present study indicate that the protein and other nutrients of banana and fresh maize leaves are valuable supplements in fishmeal-based diets for grass carp as they meet the nutritional demands and excel a fast growth of these fish. The findings clearly show that fresh and dry leaf material can be differently digested by grass carp; moreover the study clearly shows the role of dietary plant fibres and some antinutrients on nutrient assimilation in grass carp. The information provided in this study is a good base for scientists and extension workers for the development of improved feeding strategies in many tropical poor countries in the world based on plant materials available locally for herbivorous fish like grass carp. These findings should be further tested under pond conditions as they could lead to an increase of fish productivity with plant based feeds and enhance the livelihood of the small-scale farmers in the rural areas.