Feeding Herbivores, Carnivores and Omnivores

How to match diet to feeding type: carnivores need high-protein meaty foods in larger, less frequent meals; herbivores need algae, plant matter and fibre and graze often; omnivores need variety - and why the wrong diet can cause bloat and fatty liver.

Before choosing food, identify whether a species is a carnivore, an omnivore or a herbivore (Merck Veterinary Manual). Fish have evolved digestive systems suited to their natural diet, so matching the food to the feeding type is one of the most important things you can do to keep them healthy.

Match the diet to the feeding type

• Carnivores - high in protein and fat; meaty foods such as whole prey, bloodworm and frozen or live foods; larger meals, less frequently.
• Herbivores - algae, vegetables and other plant matter; more fibre and low animal protein; small amounts grazed frequently through the day.
• Omnivores - a mix of plant and animal foods; they thrive on variety and small, regular feeds.

Many fish need a higher proportion of protein in their diet than other vertebrates do, and carnivores sit at the top of that range while herbivores need more fibre than carnivores (Merck Veterinary Manual). As a rough guide to how much protein prepared diets carry, UF/IFAS reports that fry and fingerling feeds exceed 50% crude protein, grow-out diets often approach or exceed 40%, and maintenance diets may contain as little as 25-35%. Fish also require long-chain (C20 and C22) fatty acids that plant and land-animal ingredients do not supply.

Why the wrong diet is dangerous

Herbivores tend to have a small stomach and a long intestine adapted to slowly extracting nutrients from plant matter. Feeding them a rich, meaty, high-protein diet exposes them to ingredients they lack the enzymes to digest, and such food passes dangerously slowly through their long gut. In herbivorous cichlids such as mbuna, rich diets are linked to 'Malawi bloat', in which the belly swells and the fish is almost always lost (Practical Fishkeeping). Excess fat, rancid food or too much carbohydrate can also drive fatty change in the liver, known as hepatic lipidosis (Merck Veterinary Manual).

Sources: www.merckvetmanual.com , www.merckvetmanual.com , ask.ifas.ufl.edu , www.practicalfishkeeping.co.uk