Guerrero-Bravo, José E.

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    Fluorescence-based assessment of total protease activity/trypsin as a function of variable soybean content in fines fed to the gray tilapia (Oreochromis niloticus) and the red tilapia (Oreochromis hornorum)
    (2007) Guerrero-Bravo, José E.; Uscian, John M.; College of Arts and Sciences - Sciences; Santos, Carlos J.; Montalvo, Rafael; Department of Biology; Pérez Muñoz, Fernando J.
    This study evaluated the effect of five diets, differing from one another based upon ratio of raw soybean/processed soybean content, upon both biomass production and intestinal protease activity in gray tilapia (Oreochromis niloticus) and red tilapia (Oreochromis hornorum). The tilapia were maintained for 5 weeks in a Lajas’ Aquaculture Facility pond, Lajas, Puerto Rico. This pond contained 5 separate cages and each cage contained 16 male tilapia, 8 of which were gray and 8 of which were red. These fishes were provided with one of the following five diets (i.e., 0:4, 1:3, 2:2, 3:1, or 4:0 for raw soybean/processed soybean protein dietary component). At the end of the feeding period, the following were determined: 1) weight, 2) total intestinal protease activity (determined by fluorometric assay), 3) amount of intestinal protease activity attributable to the enzyme trypsin, 4) feasibility of purifying and characterizing trypsin from red or gray tilapia, 5) in vitro examination of how the addition of processed soybean homogenate affects intestinal protease activity, and 6) SDS-PAGE zymogram visualization of the effect of increased processed soybean homogenate on total intestinal protease activity. Although an increase in biomass >5% for gray tilapia and >21% for red tilapia was observed, a linear correlation between increased raw soybean feed content and biomass production was not observed. The in vitro assays revealed that intestinal proteases of both red and gray tilapia are inhibited by processed soybean homogenate. This effect was greatest for gray tilapia. Trypsin was partially purified from both tilapia species and found to display a pH optimum of 8.0, highest catalytic rate at 50 oC, and a molecular weight of approximately 23 kDa. In addition, in vitro soybean trypsin inhibitor analysis revealed that 82-86% of the total intestinal protease activity was attributable to trypsin, a finding similar to that from similar analysis of other fish species.