Browsing by Person "Greiling, Alexander Michael"

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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.