The Gastrointestinal Tract of Fish - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 1

1 The Gastrointestinal Tract of Fish

Arun Kumar Ray 1 and Einar Ringø 2
1 Department of Zoology, Visva-Bharati University, West Bengal, India
2 Norwegian College of Fishery Science, UiT The Arctic University of Norway

ABSTRACT

The organization of the gastrointestinal (GI) tract of fish follows the basic features as in other
vertebrate groups with a degree of variation in phylogeny and ontogeny, feeding habits, diet,
nutrition, physiological conditions and the special functions the gut may perform. There are
enormous variations in the morphology of the GI tract among various fish species. The varia-
tions in the organization of the GI tract ensure optimum utilization of dietary nutrients, which
in many cases means efficient primary digestion and a large intestinal absorptive surface area.
Different fish species have adapted different approaches to accommodate this objective. Of
particular interest to fish nutritionists is the comparison of morphological features in relation
to natural diets. In order to compare data obtained from one fish species with other species, it
is essential to make divisions into a broad line of common morphological features.

1.1 INTRODUCTION

Detailed descriptions of the anatomy and physiology of GI tracts of numerous fish species have
been covered in several reviews (Suyehiro 1942; Barrington 1957; Kapoor et al . 1975; Harder
1975; Fänge and Grove 1979; Smith 1989; Stevens 1988; Olsen and Ringø 1997; Wilson and
Castro 2011). Fish have the ability to rapidly and reversibly adapt GI tract characteristics to
match the changes in functional demands that occur during their life history (e.g. metamorpho-
sis, anadrome or catadrome migrations) or more frequently (day-to-day or seasonal shifts in
diet or environmental conditions); this ability is dependent on endocrine signalling pathways
which are augmented by the enteric nervous system (Karila etal . 1998). The wide diversity and
levels of hormones and signalling molecules secreted by the numerous types of GI tract and
endocrine pancreas cells allow fish to rapidly and reversibly alter characteristics of the GI tract