Browsing by Subject "Fische"

Now showing 1 - 2 of 2

Nutritional evaluation of oilseed press cakes in fish nutrition with emphasis on rainbow trout (Oncorhynchus mykiss, W.)
(2019) Greiling, Alexander Michael; Rodehutscord, Markus
Fishmeal is a valuable, protein rich ingredient for fish feed. It is a source of highly digestible crude protein (CP) with a balanced amino acid (AA) profile, well digestible inorganic phosphorus (P), and a highly digestible energy content. However, its availability is decreasing owing to an increasing demand that is driven by the increased production of fish in feed-based production systems. Research has made great advances in counteracting the limited supply of fishmeal. As a result, the majority of dietary CP in fish feed is made available from oilseeds and their processed by-products. Despite the pre-existing research efforts, the continuous evaluation of feed ingredients in search for alternatives to fishmeal is key to facilitate a sustainable growth of feed-based fish production. Oilseed press cake represents a widely available source of CP. While numerous studies have evaluated the nutritional value of press cake in fish feed, the majority focused on species reared in warmwater production systems. Thus, the objective of this thesis was to add to pre-existing knowledge on press cake and its potential to replace fishmeal in fish feed, with special emphasis on rainbow trout (Oncorhynchus mykiss W.). Initially the nutrient digestibility of various press cakes (linseed, pumpkin seed, rapeseed, soybean, sunflower seed, and walnut kernel cake) was determined in rainbow trout. The press cakes differed greatly in their digestibility of crude nutrients, with CP digestibility ranging from as low as 25% (sunflower seed cake) up to 88% (pumpkin seed cake). Another digestibility experiment was conducted using rapeseed cake and sunflower seed cake whose fibre fractions were reduced using two different processing methods (sieving and dehulling of seeds prior to pressing). The fibre-reduced press cake of rapeseed and sunflower seed cake had a substantially higher CP digestibility than their unprocessed counterpart (Manuscript 1). Three growth experiments were conducted to study the effect of partial replacement of fishmeal with press cake on performance traits of rainbow trout. In all growth experiments groups of rainbow trout were fed with either a basal diet or diets in which fishmeal CP was in part replaced by press cake based on its CP digestibility that was determined in the preceding digestibility experiments. It was found that the performance traits were influenced to a different extent in dependence of the press cake and their inclusion level. Pumpkin seed cake has been shown to have the highest potential to replace substantial amounts of fishmeal of the basal diet without significantly reducing performance traits of rainbow trout. To investigate the potential utilisation of InsP-P and the formation of inositol phosphate isomers in fish two experiments were conducted. The single and interactive effects of a mineral P supplement (monoammonium phosphate; MAP; 1 g P/kg DM of diet) and an InsP6 hydrolysing enzyme (Aspergillus oryzae 6-phytase; 2800 FTU/kg DM diet) were compared between rainbow trout and Atlantic salmon (Salmo salar). For each species a digestibility experiment was conducted under common rearing conditions of each species but using the same four diets (basal diet, basal diet + MAP, basal diet + phytase, and basal diet + MAP + phytase). The faecal disappearance of InsP6 was generally low (approximately 8%) but similar between the species when the diets were devoid of either supplement. The supplementation of phytase significantly increased InsP6 disappearance in both species, but the effect was found to be more pronounced in rainbow trout. The analysis of lower inositol phosphate isomers revealed that their hydrolysis progressed to a greater extent in rainbow trout and it suggested that InsP6 is subject to a different degradation pathway in the two species. While no significant interactive effects on InsP6 disappearance were found between the two supplements for either species, the MAP supplementation slightly decreased InsP6 disappearance in Atlantic salmon but not in rainbow trout. The experiments provide an insight into the breakdown of InsP6 and the faecal appearance of specific lower inositol phosphates and suggest that the use of press cake in feed for rainbow trout seems to be more beneficial than in feed for Atlantic salmon with regards to a more sustainable use of P resources. However, more experiments are recommended to complement these initial findings to gain a better understanding of InsP6 hydrolysis in fish.
Saponin fractions from fenugreek (Trigonella foenum-graecum L.)as dietary supplements for Nile tilapia (Oreochromis niloticus L.)and common carp (Cyprinus carpio L.)
(2012) Stadtlander, Timo; Focken, Ulfert
The future role and importance of aquaculture for the world food supply is more and more recognized by the public. High quality feed for semi-intensive and intensive aquaculture operations are necessary to guarantee a future continuous growth of fish production. Nutrient utilization efficiency has in the past been augmented by addition of feed additives, mainly anti-biotics and hormones. That practice is prohibited in the European Union since 1st of January 2006 and the consumer acceptance of products produced in that way is low. Around a decade ago saponins, secondary plant metabolites, have been found to be potential alternatives for aquafeeds. Saponinmixtures derived from the South American soap bark tree Quillaja saponaria, have been found to have beneficial effects on growth, feed and nutrient utilization and on metabolism of common carp Cyprinus carpio and Nile tilapia Oreochromis niloticus. Furthermore, in one of the early experiments a sex ratio in favor of males was observed in saponin fed tilapia compared to control fish not supplemented with saponins. An influence on sex ratio of Nile tilapia would be highly desirable since industrially Nile tilapia production is only financially viable if all male populations are produced since mixed sex tilapia populations tend to reproduce uncontrollable. The production of all male tilapia populations is mainly conducted by feeding the potentially environmentally hazardous and carcinogenic synthetic hormone 17--methyltestosterone to sexually undeveloped tilapia fry. The above mentioned problems led to a joint research project with partners in Israel and Palestine in which this dissertation has been conducted. The aim of the project was the fractionation of crude saponin extract derived from fenugreek Trigonella foenum-graecum and its testing in vitro and in vivo. It was assumed that a higher biological activity could be achieved if saponin fractions instead of crude mixtures would be applied. After in vitro testing, different saponin fractions or eluates, have been tested on their effects on growth, feed and nutrient utilization, metabolism, proximate composition, gene expression of GH and IGF-1, sex ratio, reproduction and gonad histology. Most of the feeding experiments were conducted with Nile tilapia but one experiment was also conducted with carp. Three of the feeding experiments have been conducted in a system capable of measuring continuous respiration of the fish. Another experiment has been conducted at a field station at Jericho, Palestine. The experiments conducted to evaluate the influence of saponin fractions on sex ratio of undifferentiated tilapia fry have been conducted primarily in a flow-through system. The tested saponin fractions and a tested sapogenin are not suitable to produce male monosex tilapia populations. The sex ratios after supplementation of diets of mixed sexed tilapia fry did only in one case show a significantly higher proportion of males than the control. In a larger scale repetition of that experiment the previous observations could statistically not be proofed. It must be assumed to be random effects or be the result of initially biased sex ratios after stocking undifferentiated tilapia fry. An experiment in which genetically female tilapias were fed with two fenugreek saponin fractions and positive and negative controls supported that finding. A long term feeding experiment conducted at Jericho revealed no influence of the long and short term supplemented Q. saponaria saponin mixtures on sex ratio and reproduction of genetically female tilapia. A similar laboratory experiment with fenugreek saponin fractions could not be evaluated in that regard. The experiments evaluating the effects of the saponin fractions on growth, feed and nutrient utilization, gene expression of GH and IGF-1 and proximate composition revealed no significant differences. But in all experiments one fraction eluated with 60%/40% (v/v) methanol/water showed numerically improved values compared to control and other fractions. Furthermore one fraction eluated with 40%/60%/ (v/v) methanol/water gave constantly numerically inferior results of tested parameters compared to control. That supports the conclusion that the 40% methanol fraction contains saponins generally referred to as anti-nutrients. In only one experiment, conducted at Jericho, significantly higher growth was observed after long term supplementation with a Q. saponaria saponin mixture containing elevated sapogenin content. The presented data in this thesis is not supporting an application of the tested saponin fractions as environmentally friendly alternative to methyltestosterone to produce all male populations of tilapia or to inhibit uncontrollable reproduction. Additional experiments are needed to evaluate different modes of application like immersion treatments or injections since during the experimental work of this thesis all tested saponins were added to the feed. An application of the tested fenugreek saponin fractions as growth promoters yields a higher potential although the experimental results are based upon low sample sizes due to capacity restrictions of the respirometric system. Therefore a repetition under near commercial or commercial conditions must be considered.