Evaluating silage oil from rainbow trout (Oncorhynchus mykiss) viscera as a substitute for dietary fish oil on production parameters of juvenile African catfish (Clarias gariepinus)

Patience, Ashley O'Brian (2020-03)

Thesis (MScAgric)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Fresh rainbow trout (Oncorhynchus mykiss) viscera was used to extract fish silage oil by acid and fermentation ensiling methods. Organic acid mixtures (lactic acid x formic acid, lactic acid x propionic acid, and a commercial bacterial inoculum x molasses) were added to about 900 L of minced viscera in three airtight 1000 L, respectively. The silage oils were assessed for their volume, quality and fatty acid composition with the view to being used as feed oil in African catfish (Clarias gariepinus) diets. After 30 days, across the treatments, an average volume of 291 L of silage oil was produced, with a quality deemed favourable by food grade standards. The silage oils were very similar in their fatty acid fatty acid composition and compared favourably to a regular marine-based feed oil in their percentage of polyunsaturated fatty acids. However, the silage oils had a low percentage of omega-3 fatty acids and a high percentage of omega-6 fatty acids, resulting in a high omega-6:omega-3 fatty acid ratio. A 90-day feeding trial was conducted to investigate the effects of replacing fish oil with rainbow trout (O. mykiss) silage oil in the diets of juvenile African catfish (C. gariepinus), on their growth, survival and feed conversion. The three silage oils (derived from a lactic acid x formic acid silage, lactic acid x propionic acid silage, and a commercial bacterial inoculum x molasses silage) and a marine fish oil (control) were evaluated as the feed oils in four treatment diets. The diets were fed to juvenile African catfish (1.36 ± 0.14 g) in six replicate tanks per treatment, over a period of 92 days in a temperature-controlled recirculating aquaculture system. Overall there was no significant difference (p>0.05) between the four treatments on growth, survival and feed conversion ratio. The results indicate that the total dietary replacement of marine fish oil with Rainbow trout silage oil does not significantly affect the growth, survival or feed conversion of juvenile African catfish after a 92-day feeding trial, and that Rainbow trout silage oil could prove to be a viable alternative to fish oil for juvenile African catfish in the 1.36 – 53.33 g size range. This bodes well for the sustainable utilisation of Rainbow trout visceral waste as an aquafeed ingredient.

AFRIKAANSE OPSOMMING: Vars reënboogforel (Oncorhynchus mykiss) viscera was gebruik om viskuilvoerolie te onttrek deur suur- en fermentasie-inkuilingsmetodes. Sowat 900L elk van gemaalde viscera is in drie lugdigte 1000 L plastiekhouersby melksuur x maursuur, melksuur x propionionsuur en 'n kommersiële kuilvoerinokulum x melasse bygevoeg. Die kuilvoerolies is geassesseer vir volume, gehalte en vetsuursamestelling met die oog daarop om as voerolie in Afrika-katvis (Clarias gariepinus) -diëte gebruik te word. Na 30 dae, oor al die behandelings, was daar ‘n gemiddeld van 291L viskuilvoerolie gevorm met ‘n voedselgraadstandaard gehalte. Die kuilvoerolies was baie soortgelyk in hul vetsuur-samestelling, en is gunstig vergelyk met 'n standaard mariene olie in hul persentasie poli-onversadigde vetsure. Die kuilvoerolies het egter 'n lae persentasie omega-3-vetsure en 'n hoë persentasie omega-6 vetsure gehad, wat 'n hoë omega-6: omega-3 vetsuur verhouding tot gevolg gehad het. 'n Opvolgstudie is uitgevoer om die effekte van die vervanging van visolie met reënboogforel (O. mykiss) kuilvoerolie in die dieet van jong Afrika-katvis (C. gariepinus) te ondersoek, oor hul groei, oorlewing en voeromsetting. Die drie kuilvoerolies (afkommende van melksuur x maursuur kuilvoer, melksuur x propionionsuur kuilvoer en 'n kommersiële kuilvoerinokulum x melasse) en die mariene visolie (kontrole) is geëvalueer as die voerolies in vier behandelingsdiete. Die diëte is aan jong Afrika-katvis (1.36 ± 0.14 g) gevoer, in ses replikaat tenke per behandeling, oor 'n tydperk van 92 dae in 'n temperatuur-gekontroleerde hersirkulerende akwakultuurstelsel. Oor die algeheel was daar geen beduidende verskil (p>0.05) tussen die vier behandelings op groei-, oorlewing- en voeromsettingsverhouding nie. Hierdie resultate dui daarop dat die totale dieetvervanging van mariene visolie met reënboogforel kuilvoerolie nie die groei, oorlewing of voeromsetting van jong Afrika-katvis na 'n 92-dae voedingsproef beïnvloed het nie, en dat die reënboogforel kuilvoerolie as 'n lewensvatbare alternatief vir mariene-visolie kan dien vir jong Afrika-katvis in die grootte 1.36 – 53.33 g kan dien. Dit lyk belowend vir die volhoubare benutting van reënboogforel visserale-afval as 'n akwavoer bestanddeel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107982
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