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A4 Nutrition and Nutritional Support
Lisa A. Hoopes1 and Elizabeth A. Koutsos2
1 Georgia Aquarium, Atlanta, GA, USA
2 Koutsos Consulting LLC, Apex, NC, USA
Introduction
Proper nutrition is a cornerstone of good health and a key component of preventative medicine programs. Poor nutrition impacts animal welfare and immune function and can tip the balance between health and disease. Understanding nutritional requirements is integral to the long‐term management of species under human care and fish are no exception. Good nutrition of fish can prevent diseases, reduce the severity of clinical signs, speed recovery, and help individuals overcome environmental stressors. The goal of this chapter is to summarize the nutritional requirements of fish and to review feeding, supplementation, and nutritional support.
Natural History
An appropriate diet for fish consists of essential nutrients (proteins, lipids, carbohydrates including fiber, vitamins, and minerals), in a suitable formulation that is often similar to the wild diet, and adapted to the life stage and conditions under which the animal is managed. Most studies on fish nutrition have focused on species that are routinely cultured for food (e.g. salmon, trout, tilapia, and catfish), where the goal is often rapid growth and efficient production. Little information exists on the nutrient requirements of fish kept in zoos and aquariums and in the home, where the goal is to optimize health to enhance longevity and reproductive success. In the absence of information on nutrient requirements, understanding the wild diet and foraging ecology, metabolism and energetics, and anatomy can help in choosing appropriate items to feed.
Wild Diet and Foraging Ecology
Fish can be broadly grouped into simple trophic categories based on the types of food consumed: carnivore, omnivore, herbivore, and detritivore. However, it should be noted that while a carnivore is well‐defined (consumer of animal prey), what constitutes an omnivorous, herbivorous, or detritivorous fish varies widely. Most fish species are primarily carnivorous or omnivorous; only 5% of fish families include herbivorous species (Bone and Moore 2008).
Carnivory is seen in all elasmobranchs (as predators or filter feeders) and some bony fish (often pelagic species and ambush predators). Omnivory is common in bony fish found in zoos and aquariums. Herbivorous fish include both freshwater and marine bony fish that consume vascular plants, micro‐ and macroalgae, detritus, and even wood in some species of catfish (German and Bittong 2009). Herbivorous fish that are commonly displayed or cultured include most parrotfish (Scaridae) and some tilapia (Oreochromis and Tilapia spp.). Detritivorous fish include many species of mullet (Mugilidae), some surgeonfish (Acanthuridae), and some aquaculture species including smallscale yellowfin (Plagiognathops microlepis).
Nutritionally appropriate diets for carnivorous and omnivorous fish can be based on known prey items. However, designing nutritionally appropriate diets for herbivorous grazers and browsers can be challenging, as they often feed on a complex mixture of plants, algae, and detritus.
In addition to the types of foods that fish eat in the wild, understanding normal feeding patterns and seasonal changes in the diet and environment are important in determining diets for fish under human care.
Metabolism and Energetics
Intake needs can be estimated using predictive equations of the energy requirements of a species and the estimated or determined energy content of a food item. Energetic requirements are regulated by various factors including body weight (BW). Requirements are usually expressed in units of metabolic weight, allowing scaling for a variety of body sizes. For fish, metabolic weight is generally defined as body weight (kg)0.80 (NRC 2011). This scaling means that smaller fish should be fed at a higher percentage of body weight than larger fish. Other factors also affect energetic requirements, particularly activity level (e.g. feeding, breeding, or changes in water flow) and water temperature, with relatively linear increases in energy expenditure with increasing water temperature (NRC 2011).
There are several published equations to calculate maintenance energy requirements of fish, but they vary dramatically by species and water temperature (NRC 2011). For example, the estimated maintenance energy requirements of rainbow trout (Oncorhynchus mykiss) vary from 4.54 to 17.93 kcal/kg0.80 (NRC 2011). With few energetic requirement equations available, and differences based on species, body size, activity level, and water temperature, these estimates of intake needs should be used as a guide only. Animals should always be fed to appropriate body condition.
Anatomy and Digestion
The gastrointestinal (GI) tract anatomy of fish differs based on evolutionary, dietary, and environmental constraints. The stomach in most species is a simple sac. There is no stomach in the jawless fish, e.g. hagfish and lamprey (Agnatha). The stomach has been secondarily lost in disparate teleost lineages, including members of the families Cyprinidae (goldfish, carp, and koi), Labridae