It is a must for any hobbyists to know and understand the dietary and nutritional requirements of fishes for better up-keeping of these loved pets. Remember, more you have the knowledge of proper nutrition of the cultured fishes, better you are equipped to take good care for your aquarium pets.
You can yourself prepare nutritious, cost-effective diets for your fish once you know the nutritional requirements of the species. You have to meet those requirements formulating a balanced diet and applying appropriate feeding practices. Let’s see what nutritional facts you must keep in mind while rearing your aqua pets.
Fish Diet Constituents
A fish feed can be easily manufactured from finely ground meals, crumbles, and pellets of various sizes. Most of the diet forms are solid with 10 percent moisture. The feeds must be frozen, refrigerated or have long term storage. Pellet mills generally use steam to moisten and heat the feed. The moisture retention is 15-18 percent, and the temperature ideal for feed is 150 to 185 degree Fahrenheit. Extrusion processing also uses a preconditioning chamber so that the feed mixture gets the required steam and heat. While the mixture passes through the extruder barrel, a considerable amount of heat is produced.
In the case of smaller fishes, diet forms can be introduced in various methods. They involve the procedure of microbinding, microencapsulation, and microcoating. The size of the feed varies from 25 to 400 microns. Process of manufacturing the diet of fishes depends upon the fish’s nutritional needs but also matches the diet’s physical characteristics.
When to Feed Fish
There is no specific or standard procedure for fish feeding. While you feed, it’s essential to consider the life cycle of the fish, water temperature and fish metabolism. Below stated are some general practices that you should try to follow:
• The schedule of feeding should be based on the size of fish or might be the water temperature. You should administer prescribed amounts at specific intervals. As the fish size increases, the feeding quantity and frequency should be reduced.
• In case of large ponds, the fish is generally fed to apparent satiation. The fish is provided with feeds every 20-30 minutes. Demand feeders can also be used for particular circumstances.
• As regards young fishes, you should try to feed them at a regular frequency and at regular intervals. In case of relatively smaller places like raceways, cages or nets there is always intensive flows through recirculation of water.
• You may consider feeding your fishes with medicated feeds. Administer them with commercial antibiotic products like oxytetracycline, ormetoprim, florfenicol, and sulfadimethoxine. Proper feeding rates and withdrawal time must be followed by hobbyists.
Nutritional and dietary requirements of fish
The major nutrient groups required by fish are – proteins and amino acids, carbohydrates, lipids and other micronutrients like minerals and vitamins.
The body of fish requires various macronutrients like proteins, carbohydrates, and lipids. It utilizes these elements for metabolism and different other body functions. There are variations in food habit as fishes are generally carnivorous, herbivorous and omnivorous by nature. While the carnivorous species use the dietary protein for energy, they are lesser efficient in using carbohydrates for energy yield. Generally, a certain amount of digestible energy provided by feed gets lost in energy.
- Proteins and Amino acids
Proteins consist of amino acids, the composition of which gives proteins their individual characteristics. Biochemicals required for normal bodily functions are hormones, enzymes, and immunoglobulins. The amino acids that are mandatory in the diet are “essential” or “indispensable” amino acids. There are ten essential or indispensable amino acids which are the quantitative dietary requirements for many fish species.
However, there are also ten non-essential or dispensable amino acids which their body can synthesize from various other sources. It is very crucial to meet the minimum dietary requirement consisting of protein, or a balanced mixture of amino acids for the adequate health and growth of the fish. Herbivorous and omnivorous fishes require 25-30 percent of crude protein while carnivorous fishes require 40-50 percent of the same.
In some instances, the deficiency of amino acids manifests in the reduction of weight. For certain species, the deficiency of tryptophan or methionine may lead to pathological conditions as amino acids are not incorporated into proteins. Deficiency of tryptophan may also result in scoliosis, a condition that leads to a decline in the levels of the brain neurotransmitter serotonin. Fishes can naturally convert phenylalanine to tyrosine so that they can meet the requirements of aromatic amino acids.
As a matter of fact, fishes don’t have any specific requirement of carbohydrates in diets. They tend to utilize dietary carbohydrates for various energy-yielding purposes. Carnivorous fishes for example hardly have any use of carbohydrates as compared to the omnivorous and herbivorous species. Carbohydrates are generally deposited in the form of glycogen inside tissues like liver and muscles and it is a source from where energy is readily available. There is also a little dietary carbohydrate which is deposited in the body after getting converted into lipid for energy.
Carbohydrates can be of various size, shapes, and complexity that usually get synthesized via photosynthesis. The glycogen reserve is generally utilized when the fishes require carbohydrates, and it can also be mobilized rapidly when the fish body is in need of glucose. In addition to energy, soluble carbohydrates like starch in fish provide pellets integrity and also stability.
Fishes, when fed with a high concentration of digestible carbohydrates, have resulted in increased liver and glycogen content. While in some cases, oral inception of glucose resulted in persistent glycemia. Carbohydrates are also regarded as the least expensive source for dietary energy.
Lipids are a nutrient group consisting of several compounds. Neutral lipids are present in the form of triglycerides, and they provide a concentrated source of energy for aquatic species. Dietary lipids are said to provide essential amino acids that are generally not synthesized by organisms.
Most marine fishes have HUFA as component of the cell membrane and it is present in the neural tissues of the eye and brain. They are the primary source of highly active Eicosanoids that are responsible for blood clotting, inflammatory and immunological responses, cardiovascular tones and also renal functions. Deficiency of fatty acids reduces the tendency of weight gain, but after a certain amount of time. Mobilization of fatty acids normally occurs from the exogenous tissue lipids. Neutral lipids, which are usually found in the form of fats and oils or triglycerides, act as a source of energy for the aquatic animals. Dietary lipid tends to provide essential fatty acids that cannot be synthesized by an organism.
The essential fatty acids are components of phospholipids in all bio membranes and act as precursors thereby fulfilling a variety of metabolic functions. During the acclimation of cold water temperature, the total amount of phospholipid inside the fish membrane doesn’t change. Dietary lipids contain both saturated and unsaturated variety, which is determined by the carboxyl or the methyl terminal. The freshwater fishes require dietary linoleic acid or linolenic acid. The most prominent signs of EFA deficiency in fishes are denoted by dermal signs like fin rot, shock syndrome or reduced growth rate. The low concentration of n-3 PUFAs cause diseases like scoliosis and/or under-developed swim bladder in red sea bream larvae.
The aquaculture conditions and feeds used in the fish aquaculture cause variation in the fatty acid composition of the fish. There are various factors responsible for the cause of variation in fatty acids. The reasons depend upon fish bio-ecology, feeding habits, lipid content and the nature of wild or farmed fish.
The fish body requires various inorganic elements for multiple purposes. They can be used for body functions like tissue formation, osmoregulation, and various other metabolic functions. Minerals are mainly classified into two broad categories namely micro and macro, depending on the quantity the fishes like to store inside their body. The minerals that generally fall into the macro category are- phosphorous, magnesium, calcium, sodium, chloride, sulfur and potassium. But, the most significant macro element present in fish is phosphorous and excreted phosphorous results in eutrophication of water. They are also the major mineral present in fish scales and bones. When there is a lack of phosphorous, fishes tend to suffer from reduced tissue mineralization, and you can even find impaired skeletal formation in juvenile fish. The vital electrolytes involved in osmoregulation are sodium, chloride, and potassium. Various supplements in the fish diet are also supplied by selenium, zinc, manganese, iron, and copper.
Vitamins are essential for several fish species. These are organic compounds which are required relatively in smaller amounts to control the metabolic functions of the body. Vitamins are divided into two broad categories based on solubility, and they are fat soluble and water soluble vitamins. The fat-soluble variety includes Vitamin A (retinol), Vitamin D (cholecalciferol), and Vitamin E (alpha-tocopherol) and also Vitamin K. These vitamins generally remain deposited and associated beneath body lipids. Fishes usually can survive for hours without these fat-soluble Vitamins, but generally, show their deficiency after long hours.
The various water-soluble vitamins required for fish health are- vitamin A, vitamin D, vitamin E and vitamin K. They are essential for the maintenance of epithelial tissue, bone calcification, as parathyroid hormone, as a biological antioxidant and for clotting of blood. Water-soluble vitamins include ascorbic acid, choline, folic acid, niacin, inositol, pyridoxine, thiamin, riboflavin, and vitamin B. These water-soluble vitamins are generally coenzymes that serve specific metabolic functions.
You can get various vitamin premixes readily available in the market so the fishes can be fed, irrespective of multiple dietary ingredients. The stability of vitamins over feed manufacture and other storage have been improved with age. Vitamins are evident in various types of fish feed, particularly in the multiple forms of most labile ascorbic acid.
What are the various digestion and metabolism impacts on fishes?
When the fishes absorb prepared feeds, it’s broken down to simpler versions by digestive juices and fluids which are then absorbed from the gastrointestinal tract back to the bloodstream. The digestion process is similar to the monogastric animals, which involves physical, chemical and physiological processes.
Protein digestion begins inside the stomach, while it creates a low PH environment that results from hydrochloric acid secretion and some proteolytic pepsin enzyme. The enzymes help in the breakdown of complex protein, carbohydrates, and lipids into smaller molecules which are eventually absorbed in the bloodstream of fish.
The liver plays a significant role in directing various nutrients to specific organs. The conversion of amino acids, lipids, and carbohydrates into energy occurs here. There should be a proper balance in the dietary protein to energy conversion to optimize the fish growth and lean tissue accretion.
What sort of feeding ingredient do you need to prefer for the fish?
The byproducts of the plants and animal products for human food are actually processed for fish feed. Most of the ingredients have a limited level of ingredient, or there might be an anti-nutritional factor which is included in the diet in certain limits. Complimentary ingredients are usually mixed to meet the various nutritional requirements of fishes.
Protein supplements generally consist of 20 percent crude protein, but the energy concentrate has lesser than 20 percent crude protein and also 18 percent fiber. The plant feedstuff found in various protein supplement categories are cottonseed meal, canola meal, soya bean meal, and different other protein concentrates like cereal grains, corn gluten, wheat gluten, and various distillers’ dry grain.
You should prefer reliable estimates for nutrient requirements which have been established for the dominant culture of fishes. These are the most suitable for species whose natural feeding habit along with environmental requirements found to be similar. We hope that this article has been useful in providing necessary information on the nutritional value and suitability factor of common feedstuffs that you can apply while taking care of your fishes.