Fish Feeding - From Tetra

http://www.tetra-fish.co.uk/tetratropical/home/index.asp

1. Feeding Biology

There is a vast amount of subject matter that we could include in an article entitled ‘feeding biology’, far more than can be covered here. Therefore we will stick to the basics – how fish find obtain / find food, the handling / digestion of food, and what fish eat in the wild. In the next article we will then translate this into providing the right diet for fish in our aquariums.

How fish find food Different species of fish employ varying tactics to find and capture food items. Initially they need to locate a suitable food source, and for this they have a number of senses at their disposal: VISION is especially important for many fish species, allowing the detection of potential food items at both long and short distance, depending on water clarity and other factors. In a clear aquarium, most inhabitants will use vision to a high degree. There are exceptions of course, such as Blind Cave tetras and nocturnal species. Indeed, in aquariums fish may use vision amongst other senses to pre-empt feeding time – the sight of a human shape approaching the aquarium can trigger the increased activity that is associated with feeding behaviour. Vision can also be important for evaluating the quality of a food item – its movement, colour and shape can all influence whether or not it is consumed. In fact, Tetra’s ornamental fish laboratories have established that certain ornamental fish prefer particular colours of food. Getting the colour right can improve acceptability, and reduce the time that food spends floating in the water before it is consumed (thus maintaining its quality). CHEMORECEPTION refers to the detection of chemical signals in the water via taste (‘gustation’) and smell (‘olfaction’). In humans, compounds that are transmitted via air are smelled, whereas those that are dissolved in a solution (food / liquid) are tasted. Where fish are concerned all compounds are dissolved in water and so there is less distinction between taste and smell – both are well able to detect dissolved chemicals in the water. However, fish do still have separate sensory systems for detecting smells and tastes. Smell Fish have openings in the snout called ‘nares’ which are used to draw water into two nasal sacs – one on each side of the head. You can see these if you look closely at your fish in the aquarium. Most species have two nares for each nasal sac, but some have just one (e.g. cichlids). The nasal sacs are lined with sensory cells that are used to detect chemicals in the water. If a chemical is picked up that the fish associates with food (e.g. certain amino acids), then it may decide to begin looking for that food particle. They are able to follow a concentration gradient to locate the source of the food – the smell becoming stronger as they get closer. Smell is especially useful for detecting food at long distances. In an aquarium, many fish will be aware of the presence of food before they smell it (through visual cues). However, timid or nocturnal species will rely on smell – for example, Spiny Eels and many catfish (which often hide away in the aquarium) have very well-developed senses of smell that will alert them to the presence of food. Taste Taste is generally less sensitive than smell and is primarily used for the final selection of a food item. Taste buds are found in the mouth in most species, and over the skin, fins and barbels in others (e.g. catfish). Taste buds on the end of barbels in catfish and loach allow them to assess a food item before consuming it. In addition, barbels are used to detect food that may be buried in the substrate, or to aid feeding at night when vision is impaired. Taste buds in the mouth will help the fish to assess a food item before it is swallowed, enabling them to separate edible from non-edible particles (e.g. sand / gravel from food granules). Other senses Other senses are also employed for finding food, such as mechanoreception (the detection of physical stimuli), and in some species electroreception. Electric catfish for example are able to stun prey with an electric shock, whereas other weakly electric fish such as South American Knife-fish and Elephant fish are able to detect smaller prey items using an electric field. Mechanoreception includes hearing and pressure-detection via the lateral line – this may also be used for picking up the presence of moving prey. It also involves ‘touch’ which is used to assess a food item once it is in the mouth. Indeed Tetra’s foods are specially formulated so that they soften quickly, making them more acceptable than ones that remain hard.

How fish obtain food It is not enough just to be able to find food – fish must also be able to obtain and consume it. Fish employ a myriad of different methods for doing this. Some predators employ ambush tactics, such as the South American Leaf fish which assumes the role and appearance of a leaf until an unsuspecting prey item swims too close. Once within reach it pounces at lightening speed to capture it. At the other extreme, browsers (such as Bristlenose catfish) are designed to graze constantly, rasping algae off rocks. For these fish, capturing food is simply a matter of having the right mouth parts to remove it. Camouflage, speed, stealth, and the physical structure of the mouth, gills, and teeth are all employed by fish to help capture food. Perhaps the most obvious adaptation to obtaining food can be seen in the design of the mouth. Look at the fish in your aquarium for example. Most of them will have mouths that roughly point forwards (‘terminal’), suggesting that they are best suited to feeding on food items suspended in the water column (e.g. Tetra Prima). Some of your fish though will be different. Many catfish and loach have ‘inferior’ mouths, positioned on the underside of their bodies. These species have generally evolved to obtain food from the substrate or off flat surfaces. Equally, some fish will have ‘superior’ mouths designed for surface feeding. Guppies are perhaps the best known example of this. This is why Tetra has developed an extensive range of foods with different properties – floating flakes / crisps (e.g. TetraPro), slow-sinking granules (e.g. Tetra Prima) and wafers / tablets (e.g. Tetra VarietyWafers). Handling and digestion of food Once obtained food must be processed and digested if it is to be of any nutritional value. This process starts in the mouth where various structures may be used to prepare food for digestion. Many fish (e.g. cichlids and cyprinids) have pharyngeal (‘throat’) teeth that are used to crush up food, and smaller particles (e.g. phytoplankton or zooplankton) will be bound together with mucus for swallowing. Following these physical processes, food is then swallowed. The ‘oesophagus’ connects the mouth to the stomach/ intestine, and food is forced down it with muscular contractions. In most fish the oesophagus serves no digestive function. Food then enters the stomach, or is delivered straight to the intestine in stomachless fish (e.g. barbs, goldfish, koi and some livebearers). The stomach is a very harsh environment in which food is broken down chemically and physically via muscular action, acids, and enzymes. It is also used to hold food for periods of time, hence its importance for carnivores that eat very high quality prey which is able to deliver a high concentration of nutrients for an extended period of time. Food then enters the intestine where it is further exposed to digestive enzymes, and the process of absorption begins. This entails the uptake of nutrients across the intestinal wall and into the body where they can be put to use. Generally speaking, fish that feed on poor quality items have longer intestines than those feeding on high quality ones. This is because poorer quality foods require a greater exposure time to remove any nutriment from them. For example, Silver Carp feed on phytoplankton and consequently have an intestine that is 13 times the length of their body.

In comparison, the fish-eating Black Sea Bass has an intestine that is only 0.71 times its body length. The importance of intestine length is less significant for aquarium fish, and all of Tetra’s diets are nutrient-rich (e.g. reasonably high protein, oil and energy levels). The advantage is that fish eat less and consequently produce less waste. Amazingly, populations of fish that are reared on good quality dry diets will often have shorter intestines than their wild cousins. From the intestine any undigested food (faeces) is then excreted. Other organs are also involved in the digestive process. For example, many fish have pyloric caeca connected with the intestine - structures that aid the digestion and absorption of food. In addition, the liver is an extremely important organ for many different reasons, including the production of bile which is stored in the gall bladder and then secreted into the intestine. Bile breaks up oils allowing them to be digested more effectively. Just like us, fish also have a pancreas that secretes various digestive enzymes into the intestine. The function and structure of the digestive system will differ depending on the natural feeding behaviour of a species, but the ultimate aim to extract and absorb essential nutrients remains the same. What fish eat in the wild The varying methods of finding, obtaining, and digesting food that are seen in different species are a result of the need to survive in a diverse environment. Fish are incredibly successful in many respects because they have adapted to different habitats and the foods that are available in them. Because different fish feed on a wide range of food items it is helpful to have some knowledge of their requirements before deciding on an appropriate diet. Broadly speaking, fish are commonly put into three different categories with respect to their diet: Carnivores principally consume animal prey, whether this be other fish (‘piscivores’) or smaller insects. Most fish prefer to feed on animal prey, which is not surprising considering its better nutritional quality compared to plants and algae. Fish that are principally carnivorous, such as Siamese Fighters, will benefit from a diet that reflects this requirement (e.g. TetraBetta). Omnivores represent the majority of fish, as most fish are adaptable to different foods (eating whatever they can find). This is where the broad classifications become a little impractical, as an omnivore in one habitat may only feed on insects, whereas in another it may feed on plants as well as insects (as fewer insects are available).

 It is not necessarily true that an omnivore in captivity will benefit from a diet containing both fish and plant material – often they will perform best on a diet based mainly on animal ingredients. If the need arises though, omnivores will make better use of nutrient-poor foods compared to true carnivores. Herbivores are the exception in the world of fish, with very few true herbivores (fish that feed almost exclusively on plants and algae). Those that are herbivorous often feed on zooplankton when young, and as adults will happily feed on animal matter if available - anyone who has lost a fish overnight will often find it being grazed on by their resident plec in the morning. Indeed, small microscopic animal life will be ingested by most herbivores during their grazing behaviour on algae and plants.

Because of this adaptability, most herbivores will happily feed on a commercial food which contains high proportions of animal proteins. However, where possible a special herbivore food should be used in order to reflect the natural feeding habits of these fish (e.g. TetraPro Vegetable). Although these three broad categories allow us to identify different natural diets, it is important to be aware of the flexibility and adaptability displayed by fish. Essentially they all require the same nutrients to remain healthy; it is simply the format that these nutrients come in that varies from one natural diet to another. This is fortunate for us, as it means that we can keep a diverse mix of fish healthy on just a few different foods, provided those foods deliver the nutrients that are required. It is also beneficial that herbivores can adapt to nutrient-rich diets, as otherwise we would have to feed them vast quantities of low quality food leading to massive waste levels.

What do Fish Live on in the Wild?

In their natural habitats, fish show a wide range of adaptations that enable them to find enough food to survive. There are three major types of fish when it comes to feeding: herbivorous fish feed primarily on plants and algae, omnivores feed on a vast range of items, from vegetable matter through to insects, small fish, and anything else that they find, and carnivores primarily prey on other animals (piscivores are carnivores that feed exclusively on fish).

There is some overlap between these classifications and it is not always clear how a particular fish should be classified. Omnivorous fish may feed on only a limited range of foods, or they may feed on a vast range of items. The majority of fish that are kept in “community” aquariums are omnivorous, accepting a wide range of foods. A good quality flake food such as TetraMin, will meet the nutritional needs of all tropical fish that are kept in community tanks.

If you do not use a good quality food like TetraMin, then you run the risk of creating excess levels of waste in the tank. Because poor quality foods are not digested as well, more solid waste is produced which ultimately breaks down in the tank, using up oxygen and releasing pollutants. Because Tetra’s foods are better utilised by fish, they also encourage better growth rates, and promote greater health and vigour than poorer quality foods. If you want the very best, then Tetra’s latest food, TetraMin Pro, is even more efficiently utilised by fish, and its unique low heat manufacturing process better preserves its nutritional content.

How Much Should You Feed and When?

Fish should ideally be fed in small meals, two to three times a day. These meals should be spaced out, preferably in the morning, at midday, and in the evening. If you are not at home at lunch-time then two feeds a day is adequate. The fish should consume all of the food within two to three minutes. Any excess should be removed from the tank so it does not have the chance to rot down. If you have fish that only feed after dark then you should add a good quality tablet food to the tank, after you have turned the lights out. Tetra’s tablet foods such as Tabimin are manufactured to the highest quality and will remain stable in the tank until they have been eaten.

aqua-fish.net