7.0 Fish Nutrition

Authors: David E. Starling, DVM and Condreay, C.

Nutrients and uses

The idea of nutrition applies to all living organisms, i.e., animals, plants, fungi, and microorganisms. “Energy-in must equal Energy-out.” This energy idea has distracted most from considering calories as the first nutrient to be calculated. There is more to remaining alive than energy intake. There are seven classes of nutrients relevant to animals (including humans). These are carbohydrates, fat, proteins, minerals, vitamins, (and water & dietary fiber). This author considers water an adequate supply for aquatic livestock if residing in sufficient volume and chemistry (See Chapter 2, Water). The focus of the discussion is that water is also an essential nutrient for fish. Dietary fiber is relatively new to the discussion in aquaculture feeds and is formulated and evaluated in commercial feeds. The osmolarity and the physiological responses are covered in Chapter 3, Anatomy & Physiology, as related to physiological needs in freshwater vs. marine habitats.

Macro-nutrients are measured in larger units of weight, such as grams. The nutrients listed above that are macronutrients include carbohydrates, fat, protein (and water, depending on habitat). Micro-nutrients are measured in smaller weight units such as milligrams or even micrograms. Minerals and vitamins are classified as micronutrients.

An essential nutrient is essential for successful nutrition, and the animal cannot formulate by in-situ biochemical or metabolic processes. Essential nutrients, sometimes called indispensable nutrients, are independent of the “macro” or “micro” classifications. Essential nutrients can be sourced by feed or symbiotic relationships, as in the traditional example of rabbits obtaining B vitamins and vitamin K from microbial sources in the caecum (part of the hindgut structurally).^[1]