A closer look at fish feeding

Karen Pattist's picture
Submitted by Karen Pattist on Mon, 11/07/2016 - 16:16

By Jessie Poon, Boronia Aquarium, Victoria, Australia


Ornamental fish keeping is a practice that dates back thousands of years, having said to have originated in China during the Song Dynasty (960 – 1279 A. D). These fish were kept for purely decorative purposes and gained much popularity, particularly among the rich due to their vibrant colours and peaceful demeanour. Since then fish keeping has spread all around the world from Europe to the Americas, and has become a luxury spared not only for the rich, but for all people as well.

The benefits of fish keeping are profound and widely acknowledged. A well-looked after aquarium brings colour and life to a home or setting, and brings a small piece of the natural world to the otherwise unnatural world we live in. To watch the flow of the water and the graceful, effortless movement of the fish can bring about a state of mental calm over the observer, evoke feelings of curiosity and joy, and has been known to be effective in relieving stress and even lowering blood pressure.

In order for our fish to keep us happy, we need to keep them happy in return. As well as creating and maintaining the right conditions for them to live in i.e. water conditions, temperature, environment, etc., adequate nutrition and feeding practices are also required for their optimum health and well-being. Fish that are under-nourished or malnourished cannot maintain health and growth, regardless of the quality of the environment they are in (Cho, 1999), so sound nutrition should be made a top priority for all fish enthusiasts.

Varieties of fish feed to suit different dietary and feeding habits of fishes

Today we are able to keep many different species of fish from various regions all around the world. The world being a vast and ecologically diverse sphere means fish species from different areas will have different dietary patterns, habits and requirements. Within regions you will also have predominantly carnivorous or herbivorous, and preferential bottom, middle and surface feeders. Luckily with today’s scientific knowledge and technology we have many varieties of fish feed to suit almost any species, ranging from pre-formed dried foods to fresh live foods. The food in which you feed to your fish should be as close to or as similar to the foods they would normally consume in their natural habitat to keep them in optimum health. Fish should also be fed with a variety of foods (i.e. dried, frozen, live) to ensure all nutritional requirements are being met, and to provide them with different stimulating flavours and textures.

Varieties of food include:

– Dried Foods: These come in the form of flakes, pellets, granules, sticks, tablets and wafers. Depending on the species you are targeting to feed, these foods can be designed to float at the top for surface feeders, sink slowly through the water column for mid-water feeders, or sink quickly to the floor for bottom feeders.

– Frozen Foods: These are usually presented as frozen into cubes in blister packs or solid blocks in resealable bags for convenience and are available from the freezer section of your local fish shop. Common components include bloodworm, brine shrimp, mysis shrimp, daphnia, tubifex worms, squid, vegetable meals and mosquito larvae. A good quality frozen food should be free from parasites, harmful bacteria and odours, and also have retained nutritional and sensorial value.

– Live Foods: The most commonly available live foods sold in fish shops include blackworm, brine shrimp, earthworms, crickets, meal worms, vinegar eels, microworms and feeder fish. Fishes are most eager to eat live foods, however, beware that some of these foods may introduce diseases to your tank.

Where do my fish eat?

Surface feeders will tend to have “superior” mouths. These are up-turned and looks a bit like a frown. Examples of these include the danios, white clouds, butterfly fish and hatchet fish. Those with down-turned mouths are termed “inferior”. Not surprisingly, these fish feed off the bottom. Some examples include various catfishes and loaches. Fishes with “terminal” mouths tend to be more versatile and can accept feed throughout the water column.

Storage to maintain optimum quality

In order for feed to be in an acceptable state when fed to fish, appropriate measures and practices must be undertaken. Incorrect storage can result in loss of nutritional value, mould growth, fat rancidity and infestation by insects and rodents. During storage, it is inevitable that the vitamins in formulated foods will degrade with time. Vitamins are highly reactive and unstable organic compounds that can be easily denatured by oxygen, heat, moisture and ultraviolet light. The rate of the loss depends largely on the vitamin and the conditions in which the food is stored. Thus dried foods should be stored away from direct sunlight in a sealed, airtight container. The conditions under which it should be stored should be cool, dry and exempt from rapid changes in temperature.

During manufacture certain measures are taken to eliminate bacteria and moulds including heat and dehydration steps, but there are certain spores of moulds that are able to survive the harshest of treatments (Soyaqua, 2008). These spores are able to become active only when favourable conditions arise, such as sufficient moisture levels and temperature. These spores grow best when the moisture content of the feed is 14.5 to 20% combined with a relative humidity of 70 to 90% (Soyaqua, 2008). Therefore moisture must not be introduced to dried foods through actions such as letting water droplets enter the container during feeding or leaving the container open for unnecessarily long periods of time.

Fish feed is generally quite high in levels of unsaturated fatty acids as they are essential for good health and growth of many fish species. Though beneficial, it renders the feed highly prone to oxidative rancidity resulting in ‘off’ odours and flavours, and so must again be stored away from direct sunlight, as this can speed up the oxidative process.

Frozen foods should be stored at a steady temperature of approximately -18oc with minimum fluctuations. These foods should not be defrosted and refrozen repeatedly as it will degrade the food value.

Live foods can be kept in the refrigerator to slow biochemical reactions, prolonging the time in which they can be kept.

How to feed fish

It is best to pour a measured amount of food into the lid of the food container and then adding this to the tank. Do not use wet fingers to retrieve food from the container as the moisture from your wet hands can cause deterioration of the food.

Nutritional Components

Nutritional components can be divided into 5 main categories: carbohydrates, proteins, fats, vitamins and minerals. Each provide fish with essential energy requirements and nutrients required for growth and everyday metabolism. Each constituent will be discussed below in more detail.

– Carbohydrates
Carbohydrates are often added as starches to fish feed formulations as binding and bulking agents, but are in actual fact not a major energy source for most fish. From 1 gram of carbohydrate, fish can only extract about 1.6 kcal, as opposed to mammals which can extract approximately 4 kcal (Craig, 2009). This is said to have arisen from the evolution of fish in aqueous systems in which carbohydrate sources were scarce, so their digestive and metabolic systems became more equipped to utilise proteins and fats for their energy needs (Lovell, 1998). Some fish however, such as warm water herbivores and omnivores are able to metabolise carbohydrates reasonably well.

– Proteins
Proteins in the diet are essential for body maintenance and muscle growth (Kesena & Arimiche, 2010) and are the primary, most efficient source of energy in fish. Proteins in fish feed are usually labelled as fish meal or shrimp meal. This component is generally the most expensive and so, some manufacturers substitute this with alternatives such as and soybean meal. Since protein is the major source of energy, it is important in assessing adequate energy needs. If a diet is deficient in energy content relative to protein content, a proportionate amount of dietary protein will be used for energy rather than tissue building. This is because energy needs for body maintenance and voluntary activity must be satisfied before energy and remaining protein is available for growth.

Amino acids are the building blocks of all proteins. Fish require twenty amino acids for growth, ten of which must be included in the diet as they cannot be synthesised within the body. These are known as essential amino acids.

Protein requirements generally are higher for small fry (baby fish), however as they grow larger, their protein requirements will usually decrease. Requirements will also vary with water temperature, water quality, genetic composition and feeding rates (Craig, 2009).

– Fats (lipids)
Lipids in fish feed provide a concentrated energy source whilst providing various other nutritional functions (Lovell, 1998). Lipids supply approximately twice the amount of energy as proteins and carbohydrates and some foods may contain up to 15% of fish diets (Craig, 2009). They also serve as a vehicle for the transportation of fat soluble vitamins (A, D, E and K) and play a crucial role in the structure and formation of cell membranes (Lovell, 1998). While warm-blooded animals have a major requirement for omega-6 fatty acids, most species of fish require omega-3 fatty acids and must be included in the diet (Cho, 1999). An explanation for this difference in fatty acid requirement is that the omega 3 structure allows a greater degree of unsaturation which is necessary to maintain flexibility and permeability characteristics at low temperatures such as in water (Lovell, 1998).

However, if a diet contains excess energy the fish may become full before they consume the necessary amounts of protein, vitamins and other nutrients for subsequent growth (Kesena & Arimiche, 2010). Excess energy, relative to protein content can cause excess amounts of visceral and body fat (Soyaqua, 2008). As such, it is recommended that fat content in ornamental fish foods do not exceed 10%.

– Vitamins
Vitamins are organic micro-nutrients required in trace amounts and are essential for normal fish growth, health and general maintenance of metabolism (Cho, 1999). Most are not synthesised in the body and so must be included in the diet. Vitamins are divided into two categories: water soluble and fat soluble. Water-soluble vitamins include: the B- group vitamins, choline, inositol, folic acid, pantothenic acid, biotin and ascorbic acid (vitamin C). The fat-soluble vitamins include: the A vitamins, retinols (responsible for vision), the D group vitamins, E vitamins, the tocopherols and K vitamins (Craig, 2009). The requirements for most vitamins will depend upon the intake of other nutrients, size of the fish, species, life stage, growth rate and external environmental stresses (Soyaqua, Fish Nutrition, Feeds and Feeding, 2008).

– Minerals
Minerals are inorganic micro-nutrients necessary in the diet for normal body functions (Craig, 2009). In fish systems, minerals play pivotal roles in osmoregulation, intermediary metabolism, and are important in the formation of the skeleton and scales (Cho, 1999).
Minerals can be divided into two subgroups; those that are required in large quantities are termed major minerals and those that are required in small amounts are terms trace minerals (Lovell, 1998). Major minerals include calcium, sodium, chlorine, magnesium, potassium and phosphorous, while trace minerals include copper, chromium, iodine, iron, zinc and selenium (Craig, 2009). In the food product labelling, major minerals are often listed.

Fish are able to absorb dissolved minerals from the surrounding water across the gill membrane or through the digestive tract and skin. In fact, most of the calcium requirements of fish are extracted from the water (Lovell, 1998). This is why it is so important to maintain the water’s general hardness within their optimal ranges.

Health and Nutritional Deficiencies

The biological definition of optimum health in fish is the absence of disease, physical stress, and the ability to maintain growth, reproduction and stable metabolism.
Reduced growth is the most common clinical sign of any deficiency, however, for each vitamin and mineral type, deficiencies may present in more specific ways. These are tabulated below (Craig, 2009)

Vitamin - Symptoms/Signs
Vitamin A - Eye/ vision problems (haemorrhagic eyes, eye lens deformation, eye lesions), oedema, haemorrhagic kidneys and skin.
Vitamin C - Anorexia, low disease resistance, slow wound healing, cartilage deformities, poor growth, scoliosis, haemorrhagic skin, liver, kidney, intestine and muscles.
Vitamin D - Scoliosis, tetany (white muscle), low bone ash, calcium, phosphorus.
Vitamin E - Nutritional myopathy, oedema, light skin colour, reduced reproductive activity, ceroid deposition, kidney and pancreas degeneration.
Vitamin K - Slow blood clotting, skin haemorrhages, anaemia
Vitamin B1 (thiamin) - Low haemoglobin, lethargy, poor appetite, skin haemorrhages.
Vitamin B2 (riboflavin) - Cataracts, cloudy eye lens, eye lesions, dark skin colouration, anaemia, fin erosion, anorexia.
Vitamin B3 (niacin) - Anorexia, oedema, lethargy, reduced co-ordination, skin lesions, loss of appetite, tetany.
Vitamin B5 (pantothenic acid) - Clubbed gills, eroded gill membranes, erratic swimming, liver necrosis.
Vitamin B6 - Convulsions, rapid breathing/ gasping, erratic swimming, nerve disorders.
Vitamin B7 (biotin) - Muscle atrophy, gill degeneration, fatty liver, colon lesions, increased skin mucous.
Vitamin B12 - Anaemia, poor appetite, low haemoglobin.

Mineral - Symptoms/Signs
Magnesium - Renal calcinosis, poor growth, lethargy.
Iodine - Hyperplasia of thyroid gland, goiter.
Zinc - Cataracts, slow growth, skin and fin erosion.
Copper - Deformed collagen and bone development
Iron - Anaemia, low haemoglobin.

Luckily for us, good quality fish foods suited to a variety of fish species are easily available at your local fish shop. The staff at Boronia Aquarium can help you choose the right kind of food to satisfy each and everyone of your fishes.

The price of good food

Remember, the price of the food is directly related to the quality. Good quality foods should have a strong fishy fragrance, similar to the smell of the fish sauce that you get at the Vietnamese restaurants.


Cho, D. P. (1999). An Introduction to Nutrition and Feeding of Fish. Fish Nutrition Research Laboratory .
Craig, H. (2009). Understanding Fish Nutrition, Feeds, and Feeding. Virginia Tech .
Kesena, E. J., & Arimiche, N. A. (2010). Improving the quality of fish feed through Omega-3-Fatty acid inclusion in diet. Agriculture and Biology Journal of North America , 654-657.
Loh, R., & Landos, M. (2011). Fish Vetting Essentials. Richmond Loh Press, Perth, 73-77.
Lovell, T. (1998). Nutrition and feeding of fish. Aquaculture Series , 55-65.
Soyaqua. (2008). Retrieved 7 22, 2011, from Storage and Handling of Feeds for Fish and Shrimp: http://www.soyaqua.org/pdf2/asafeedhandstorepub.pdf
Soyaqua. (2008). Fish Nutrition, Feeds and Feeding. Retrieved 7 29, 2011, from Soy in Agriculture: http://www.soyaqua.org/asaimusbtech/lvhdcagemanual/fishnutrition.pdf


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