Aquaculture Feed and Fertilizer Resources Information System

Rainbow trout - Natural food and feeding habits

At first feeding, the digestive tract of rainbow trout is well developed. Rainbow trout fry begin feeding in streams, consuming terrestrial and aquatic invertebrates (zooplankton and insects). Insects remain their dominant food source throughout life, although they are opportunistic piscivores (Table 1). The anadromous form of rainbow trout, called the steelhead trout, migrates to the ocean at 1–3 years of age and feeds on krill, small fish, shrimp and squid. The digestive tract of rainbow trout is about the same as body length (Figure 4). A J–shaped acid stomach is followed by the pyloric caeca, the small intestine and distal intestine (Rust, 2002). Digestive enzymes are secreted in the pyloric caeca and small intestine. Nutrient absorption occurs in both. The distal segment of the intestine plays a role in osmoregulation as a site for electrolyte secretion and absorption. Rainbow trout have a full complement of digestive enzymes, similar to other fish and terrestrial monogastric animals.