Abstract
There is increasing concern about the sustainable supply of fish meal for the aquaculture industry. This has been elevating the priority of securing alternative feed ingredients. However, alternative ingredients often rank low in digestibility. We therefore evaluated the effects of enzyme pre-treatments to enhance digestibility of such ingredients. Ingredients tested were rapeseed meal (RM), soybean meal (SM), macrophyte meal (MM; made from Egeria densa), and algal meal (AM; by-product of agar production). Each was mixed with water containing citric acid and autoclaved, after which phytases (two types) or pepsin were added and incubated (35℃-5 days). The treatment effects were evaluated by measuring in vivo digestibility using common carp. Pepsin increased protein digestibility in SM and AM (P<0.05). Phytases increased protein digestibility in SM (P<0.05). Phytases and pepsin increased phosphorus digestibility in RM and SM (P<0.01). Fecal Ca, Mg, and Zn content tended to be lower in fish fed diets containing phytase-treated RM or SM, compared with fish fed the control diets. In summary, phytases and pepsin increase digestibility of RM and SM. But, these enzymes are less effective for MM and AM. Since MM and AM are potential feed ingredients, further research is warranted on these sources.
