Comparative Biochemistry and Physiology Part A 124 (1999) 155 – 160 Activity of intestinal mucosal brush border membrane enzymes in relation to the feeding habits of three aquaculture fish species Sheenan Harpaz a, *, Zehava Uni b a Department of Aquaculture, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, 50250, Israel b Department of Animal Sciences, Faculty of Agricultural, Food and Enironmental Quality Sciences, The Hebrew Uniersity of Jerusalem, P.O. Box 12, Rehoot 71200, Israel Received 8 December 1998; received in revised form 28 July 1999; accepted 3 August 1999 Abstract The activity of intestinal mucosal enzymes in various parts of the intestine and the pyloric caeca of adult fish from three different species was examined. Selection of the fish for the study was based on their aquacultural importance and the different feeding habits they exhibit: carnivorous hybrid striped bass (Morone saxatilis ×Morone chrysops ); omnivorous tilapia (Ore - ochromis niloticus ×Oreochromis aureus ) hybrids and herbivorous silver carp (Hypophthalmichthys molitrix ). The results show marked differences among the different fish species corresponding to their feeding habits. Sucrase and maltase activities were found to be highest in the midgut of all species compared to other regions of the intestines. The lowest activity of -glutamyltranspeptidase (-GT) was found in the foregut of all species compared to other regions of the intestines. Alkaline phosphatase and -GT activities in the pyloric caeca of tilapia and bass were similar to those found in the intestines, indicating that these organs are an extension of the intestines where active protein degradation takes place. © 1999 Elsevier Science Inc. All rights reserved. Keywords: Alkaline phosphatase; Gamma-glutamyl transpeptidase (-GT); Hybrid striped bass; Intestinal mucosal enzymes; Silver carp; Tilapia www.elsevier.com/locate/cbpa 1. Introduction Growth rate in animals is dependent on the digestive system, where digestion and absorption processes take place. The digestion process includes luminal digestion and brush border membrane digestion, as a result of enzymatic activity in the digestive tract. The final stage of digestion is carried out by the intestinal enterocytes that, in the process of migration from the crypt region toward the villus tip, acquire differentiated functions including expression of brush border enzymes such as disaccharidase, alkaline phosphatase and transpeptidase [10,16,19,25]. In fish, most of the studies pertaining to brush border enzymes have been conducted with larval fish [4,5] while the activity in adult fish has been limited to wild caught fish [13,14]. Fish are capable of changing their diets during the different seasons of the year, according to the availabil- ity of food [12,21]. The digestive enzyme patterns of the fish are altered accordingly as demonstrated by [1,13,27]. Kuz’mina and Gelman [14] presented a com- prehensive review of dietary and temperature adapta- tion effects on brush border enzymes, covering an array of different fish species including salmonids. Chakrabarti et al. [6], who investigated the digestive enzymes of 11 freshwater fish species in relation to their food habits, demonstrated that, in adult fish, almost all the digestive enzymes were present irrespective of the fish’s food habits. Studies of fish proteolytic enzymatic activities have concentrated on the enzymes of the lumen and have shown that, from an early juvenile stage, the fish exhibit a full array of proteolytic enzymes [9,11,15]. Interesting extensions of the digestive tract are the pyloric caeca, which are blind tubular outgrowths around the pylorus close to the point at which the intestines follows on from the stomach. Fish without a stomach (such as the carps) also lack pyloric caeca. Within a given species, the number of pyloric caeca is * Corresponding author. Fax: +972-3-9605667. E-mail address: harpaz@agri.huji.ac.il (S. Harpaz) 1095-6433/99/$ - see front matter © 1999 Elsevier Science Inc. All rights reserved. PII:S1095-6433(99)00106-3