Significance of Fish Nutrition in Aquaculture or Aquaculture nutrition

 

E-content for Fisheries students (Series-4 Full Quadrant)

Significance of Fish Nutrition in Aquaculture

 

With capture fisheries globally being increasingly plateaued, aquaculture seems to be the only major way to suffice the increasing demand for fish & seafood. Presently, China is chief producer with 60% of entire world production, followed by India well underneath. The feed cost makes up about 60-80% of the total recurring costs in aquaculture, depending upon the type of fish species cultured and also on the intensity of aquaculture.

Fish Nutrition in Aquaculture

To develop a nutritious and cost-effective diet of a fish species, we must be aware of its nutritional requirements and its natural feeding habit. The primary aim of aquaculture nutrition is to ensure the required presence of available forms of essential macro and micronutrients in the fish diet with either entirely excluding the use of fishmeal and fish oils or at least considerably diminishing their proportions in fish feed. Fishmeal and marine oils have been persistently utilized in the manufacture of aquaculture diets, due to their superior digestibility & ideal amino and fatty acid content. However, due to the limited availability and unstable prices of fish meal and marine oil, the primary focus of research in nutrition in recent years has been on partially replacing them with cheaper and effective alternative raw materials without any significant downfall on performance and growth of fish.

Based on the gradual increasing level of human intervention in their management, farming of aquatic organisms has generally been categorized accordingly into extensive, semi-intensive and intensive aquaculture.

Extensive Aquaculture

 Extensive aquaculture is the traditional practice of aquatic farming wherein the natural productivity of ponds is boosted with the application of organic manures and chemical fertilizers and the fishes are left at low density to sustain at the mercy of nature and natural food available there in the pond.

Intensive Aquaculture

Intensive aquaculture is the business model of aquatic farming wherein the fishes are kept at a high density in tanks made of cement or frp or plastic with a continuous supply of aeration and a complete artificial feed that suffices both the macro and micronutrient requirements of fish species. Complete diets provide all the nutrients (protein, carbohydrates, fats, vitamins, and minerals) in the optimum proportion that the fish needs for proper growth and health. Most commercial feeds contain essential nutrients such as protein, lipid, carbohydrate, ash, phosphorous, water, minerals, and vitamins in the range of 18-50 percent, 10-25 percent, 15-20 percent, 8.5 percent, 1.5 percent, 10%, 0.5, and 0.5 percent, respectively.

Semi-intensive Aquaculture

This type of farming is a transition between the already explained aquaculture methods. Here, fish gets natural food from the pond but that is not enough to sustain the biomass of pond. Thus a supplementary feed is provided to ensure that fish does not remain deficient in any macro or micronutrient.

Fish nutrition particularly plays a significant role in the sustainable development of semi-intensive and intensive practices of aquaculture, influencing not only the production expenses but also fish growth, health and production of waste. A food ingredient's nutritional value is partly determined by its capacity to provide energy. In prepared diets, physiological fuel values are utilised to determine and balance available energy values. Protein, carbohydrate, and fat calories per gramme are usually 4, 4, and 9 kcal/g respectively.

In order to formulate a feed for a particular fish species, we must be aware of its feeding habits and preferable food materials. Fishes are usually divided into three types of eaters:-

1) Carnivores

Carnivores are basically scavengers of animal flesh. This sort of fish will eat anything from a minuscule crustacean or insect to an amphibian or a small animal, depending on its size.

2) Herbivores

Herbivores are mostly dependent on vegetation and decomposing organic matter in the environment for their food.

3) Omnivores

Omnivores eat practically any type of food, whether it comes from a plant or an animal source.

Fish have undergone anatomic modifications in their mouths as a result of evolutionary development. Fish can be categorised into the following categories based on their feeding habits:

Grazers: A fish that grazes in the same way that mammalian grazers does. Mullets, in general, graze continuously on the bottom of the aquatic habitat for plants or small animal creatures. Food is consumed in discrete bites.

Strainers: The menhaden is an example of a fish that selects food mostly based on its size rather than the type of food it consumes. It is possible for an adult menhaden to strain more than 6 gal of water every minute through its gill rakers. This quick straining process allows the menhaden to concentrate a very big amount of plankton and other creatures in a comparatively small amount of space.

Suckers: Buffalo fish, for example, is an example of a fish that feeds mostly on the bottom of its ecosystem, sucking in muck and filtering out digestible material before swallowing it.

Parasites: Some fish, such as the lamprey, attach themselves to other creatures and live off the fluids produced by the host animal.

Predators: Trout are an example of a predatory fish that feeds on creatures big enough to be seen with the naked eye. Teeth are well developed, and they are used to grasp and retain prey. Some predators hunt primarily with their eyes, while others use their senses of taste and touch, as well as lateral line sense organs.

Macronutrient requirements of fishes:

1) Proteins:

Protein are the most important macronutrient required in the fish feed. Proteins form the major component of organic material in the fish tissue (65-75 % on dry basis). Proteins are huge biomolecules or macromolecules made up of one or more long chains of amino acid residues. Protein in fish is required as a source of energy, for the somatic and gonadal growth, synthesis of hormones and various metabolites. It is essential that diets contain enough protein to suit the needs of animals for growth, maintenance, tissue repair, and overall health. If an enough of this macronutrient is not provided, fish will show reduced growth and will be more susceptible towards the secondary infections. Protein is typically the most expensive nutritional component due to its high cost. As a result, it is critical from an economic standpoint that diets should not include an excessive amount of protein. Proteins are not stored in the body in the same manner that carbs and fats are. As a result, an excess of dietary protein is converted to glucose or lipids as an energy deposit or used as an energy source in intermediate metabolism. In either instance, the amino acids that make up proteins must be deaminated, and the resulting ammonia is expelled through the gills and urine. Because nitrogen is one of the main elements responsible for water eutrophication (the other being phosphorus), an excess of dietary protein is harmful to the environment. Thus, from an economic and environmental aspect, it is crucial that dietary protein fulfil, but not exceed, the needs of animals. Thus, if the diet contains a low protein: high energy ratio (LP: HE), animals may stop eating before achieving their protein requirements, which can have a negative impact on growth performance and body composition. In contrast, if the meal contains a high protein: low energy ratio (HP: LE), animals would consume an excess of dietary protein, which will be catabolized and used for energy.   

Protein bioavailability must be considered when determining dietary protein requirements. If dietary protein is poorly digested, extra protein must be added to the diet to meet requirements. The protein essential amino acid (EAA) profile also influences the dietary protein demand. Dietary proteins having an EAA composition similar to the optimum protein will be required in lower quantities and used more efficiently for growth and protein deposition. As a result, the dietary protein:energy ratio, digestibility, and amino acid profile must be tuned to improve  performance of fish under culture while reducing economic feed costs and the negative environmental implications associated with feeding.

Also noteworthy is the fact that fish does not have genuine dietary protein requirements. Instead, fish, like other monogastric animals, require a well-balanced blend of both necessary amino acids and non-essential amino acids, which together make up the protein they consume. Some amino acids the fish cannot synthesize and therefore are necessary to be provided within the diet are called indispensable or essential amino acids. Essential amino acids are 10 in numbers are given as:

1. Arginine

2. Valine

3. Histidine

4. Isoleusine

5. Leucine

6. Lysine

7. Methionine

8. Threonine

9. Tryptophan

10. Phenylalanine

There are hundreds of different fish that are used for aquaculture, each with a unique feeding pattern (carnivorous, omnivorous, and herbivorous), living in a variety of environments (freshwater, saltwater, and diadromous), temperatures (cold, temperate, tropical), and growth characteristics (fast, slow growers). All of this variability may be represented in a range of nutritional requirements, however knowledge on the nutritional requirements of fish for the majority of aquaculture species is still lacking. This clearly means that the diets for the majority of animals are not necessarily the best and most nutritious because they are developed using data from other, superficially similar species. Extrapolations of nutritional requirements, even for genetically related species with similar feeding habits and living in similar environmental conditions, are not always adequate, even when the species in question is genetically close to one another. For example, the dietary protein requirements for young Diplodus sea breams, which are omnivorous and live in warm waters, have been calculated to be between 27 and 44 percent of their body weight. In aquaculture diets, protein levels range from 18 to 20% for marine shrimp, 28 to 32 percent for catfish, 32 to 38 percent for tilapia, and 38 to 42 percent for hybrid stripped bass.

Carbohydrates:

Carbohydrates are the most cost-effective and low-cost energy sources for fish diets. Carbohydrates are still included in aquaculture feeds, despite being the fact that they are not so mandatory. This is primarily done to reduce the feed costs and for the binding activity of starch during feed manufacturing.

Dietary starches, such as cassava starch, are used in the extrusion of floating feeds. Floating feeds for various finfish species are prepared with varying carbohydrate levels.

Fish have the ability to digest simple sugars efficiently. When the sugar becomes larger and more complex, its digestibility decreases rapidly. When compared to cold water or marine fish, warm water fish can digest dietary carbohydrates more efficiently. Carbohydrate utilisation as an energy source differs between species. There are no national research council recommended levels or ranges for formulating and preparing finfish and shellfish feeds.

A digestible carbohydrate source should be included in the diet. Carbohydrates promote growth and act as precursors for certain amino acids and nucleic acids. Carbohydrates are also the least expensive source of dietary energy.

Cereal grains are an inexpensive source of carbohydrates in warm water fish, but their use is limited in cold water fish. In general, digestible carbohydrates in trout feed are lower than in catfish feed. Carbohydrates show sparing effect on protein in nutrition because less protein is used for energy. Excess dietary carbohydrates can cause liver enlargement and glycogen accumulation in the liver. A diet containing no more than 12 percent digestible carbohydrates is generally recommended. Carbohydrates are also reported to increase feed palatability and reduce the dust content of finished diets. Thus, from an economical point of view carbohydrates are necessary to be added in feed so that more amount of the protein is used for growth instead of deriving energy from it, however, the majority of the energy in fish diets comes from fats and proteins.

Carnivore fish species such as eel, seabass, trout, and sea bream have a poor ability to digest carbohydrates due to low amylase enzyme production, and formulated feeds for these species contain less than 20% carbohydrates. However in case of omnivores and herbivores, 40-45% utilization of the gelatinized starch has been observed.

Fats:

Lipids (fats) represent the second most abundant group of organic compounds in animal body next to proteins. They are broadly classified as:-

1) Fats 2) phospholipids 3) sphingomyelins 4) waxes and 5) sterols.

A gram of fat has 2.5 times the amount of energy as a gram of carbohydrate or protein. Fat digestibility varies depending on the amount of fat consumed, the type of fat consumed, and the temperature of the water. The degree of unsaturation and the length of the carbon chain also are both important factors.

Highly saturated fats are difficult to digest while as the unsaturated ones are easily digested by the fishes. However, the unsaturated fatty acids are also more prone to the oxidation, thereby making fish feed more vulnerable to the process of degradation.  That’s why fish feed are included with antioxidants like vitamin E, Ethoxiquin, etc so as to prevent the fats from getting rancid during storage.

Dietary fats are an important source of energy for fish, as well as essential fatty acids (EFA), which are required for normal growth and development. These fatty acids are not synthesised by fish. Dietary fats also help with fat-soluble vitamin absorption. Linoleic and linolenic acid are required in the diet of freshwater fish. Both of these fatty acids have 18 carbons. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential nutrients for marine fish such as yellowtail and red sea bream. These are fatty acids with 20 and 22 carbons, respectively.

Micronutrients:

Vitamins are a diverse group of organic compounds that are required in minute amounts in the diet of fish to maintain normal growth, reproduction, health, and general metabolic function. They are not chemically related to one another and are only found and required in trace amounts in animal and plant foods. Fish vitamin requirements are similar to those of nonruminant animals such as pigs and chickens. Fish and humans are two of the few higher animals that require vitamin C in their diet.

Vitamins are classified into two types: water soluble and fat soluble:

Water soluble vitamis are 11 in number & include:

Vitamin B1/Thiamine

Vitamin B2/Riboflavin

Vitamin B6/Pyridoxine

Vitamin B5/Pantothenic acid

Vitamin B3/Niacin

Vitamin B7/Biotin

Vitamin B9/Folate

Vitamin B₁₂/Cyanacobalamine

Choline

Myoinositol

Vitamin C/ Ascorbic acid

 Fat soluble vitamins are 4 in number:

Vitamin A

Vitamin A is required for proper vision, growth, reproduction, infection resistance, and the maintenance of body coverings.

Vitamin D

Vitamin D aids the body's mobilisation, transport, absorption, and utilisation of calcium and phosphorous. It functions by employing two hormones produced by an endocrine gland, the parathyroid.

Vitamin E

Vitamin E, in conjunction with selenium, protects cells from the harmful effects of oxidation.

Vitamin K

Vitamin K is necessary for normal blood clotting.

Fat soluble vitamins are absorbed in the intestine along with fats in the diet. Unlike water-soluble vitamins, fat-soluble vitamins can be stored in the fish's body and, thus, if provided in excess amounts, will lead to a toxic condition in the fish, known as hypervitaminosis.

Mineral requirements of fish:

Having continuous contact with the water, a number of minerals like Calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), iron (Fe), zinc (Zn), copper (Cu), and selenium (Se) are  absorb directly from the water by fishes. As a result, the mineral requirement in the diet is reduced. However, this makes dietary mineral requirements research difficult and inconclusive. The majority of scientists agree that fish require all of the minerals that other animals do. Minerals are divided into two groups based on their requirement or use by animals: macrominerals and microminerals.

The macro minerals include the following: 

Calcium (Ca)

Chlorine (Cl)

Magnesium (Mg)

Phosphorous (P)

Potassium (K)

Sodium (Na)

Minerals such as calcium and phosphorus play a direct role in the development and growth of the human skeleton. The gills and skin of fish are capable of directly absorbing calcium from the water. So, the requirement of calcium in diet mainly depends upon the chemical characteristics of water. However, the dietary inclusion of phosphorus is more critical. Deficiency of phosphorus otherwise leads to poor growth, reduced feed efficiency and bone deformities. Magnesium is a cofactor in many enzymes, and it plays an important role in their function. Both the water and the feed are capable of meeting the dietary requirements of the animal. Deficiency in magnesium leads to anorexia, stunted growth, fatigue, deformity of the vertebrae, cell death, and convulsions, among other symptoms.

Macro-minerals are the minerals required in very minute amounts but are still very important for the proper functioning of the fish.

The microminerals include the following:

Copper (Cu)

Iodine (I)

Iron (Fe)

Manganese (Mn)

Selenium (Se)

Zinc (Zn)

Copper is an important part of many enzymes and is thus inevitable for their proper functioning. However, copper at higher concentrations can be toxic, with fish being more tolerant of copper in feed than water. Iodine has been found to be necessary to produce hormones from thyroid gland. Fishes derive their iodine requirement both from the sources of feed and water. Like in mammals, deficiency of iodine in fish leads to a condition which is similar to goiter. Iron is required in the formation of heme compounds of blood which carry oxygen. Since, natural water is deficient in iron, therefore feed is considered to be the major source of iron. However, iron at higher levels can prove to be toxic to fish and can cause reduced growth, liver damage and ultimately death.

Other dietary requirements:

Apart from the already noted macro and micronutrients, fish feed may contain water, fiber, antibiotics, antioxidants, hormones, binders, pigments and feeding stimulants.

Water

Water is present in all diets. Water can come from the feedstuff, be drawn from the air, or be added. The easier it is to store and handle a diet with less water. When a diet's moisture content exceeds 12 percent, the feed is more likely to spoil. Commercial feed of certain fishes have high moisture content as they prefer the moist feeds

Fibre:

Fiber is the indigestible plant material (cellulose, hemicelluloses, pectins, lignin and other complex carbohydrates). It does not play an important role in nutrition but adds bulk to the diet, thereby increasing the faecal output in the fish.

Antibiotics:

Among all the antibiotics, only two of them have received the FDA approval for the use in aquaculture, namely sulfadimethoxine/ormetoprim and oxytetracyclin. In United States, only licensed manufacturers are allowed to add antibiotics to feed.

Antioxidants:

Fish feeds usually have high concentrations of unsaturated fatty acids which make it more prone to oxidation and rancidity. Oxidation of fats degrades the palatability of the feed and decreases the availability of fat and some fat soluble vitamins. Synthetic antioxidants such as ethoxyquin, BHT, BHA and propyl gallate are used to prevent the oxidation of fats.

Hormones:

Various natural derived and synthetic hormones are used in aquaculture which can be incorporated with the feed. Such hormones are used either for the process of induced spawning or for the process of sex reversal (to produce monsex culture of species like salmonids, carps and tilapia).

Binders:-

They are used to hold the feed ingredients firm, thereby prevent rapid disintergration of feed particles in the water. Carboxymethylcellulose, hemicelluloses,lignosulfates,sodium and calcium bentonites are some of the widely used feed binders.

World leading companies for manufacturing fish feed are given in  the below table

Sr.No	Company	Headquarter
1.	C.P. GROUP	Bangkok, Thailand
2.	NEW HOPE GROUP	Chengdu, China
3.	Cargill	Minnesota, U.S.
4.	LAND O’LAKES	Minnesota, U.S.
5.	WINS	Yunfu, China
6	MUYUAN	Nanyang, China
7	BRF	Santa Catarina, Brazil
8	TYSON	Arkansas, U.S.
9	FARMERS	Lochem, Netherland
10	NUTRECO	Amersfoort, the Netherland

Conclusion

Fishes' growth, reproduction, and health, as well as their response to physiological and environmental stressors and pathogens, are all influenced by nutrition and feeding. Nutrition appears to be the heart of aquaculture. Feeding nutritionally optimised and enhanced feed to the fish could significantly increase overall production and increase profits in the aquaculture industry.Therefore, the primary aim should be to optimise the feed and its manufacturing for aquaculture species, thereby reducing the production costs, improving the sustainability of the aquaculture industry, and booming this business with higher profit margins. Cage culture in inland open waters is a rapidly expanding industry, and using low-quality feeds may have negative environmental consequences. As a result, the development of high-quality, low-polluting feeds for cage culture systems may help to mitigate the negative effects of aquaculture on the environment while also attracting inland fish farmers to cage culture. Fish farmers are working hard to lower the cost of fish feed, which accounts for more than half of the total cost of fish production. Many studies are currently being conducted in order to develop cost-effective feed for improving fish and shrimp production. Fish meal, which has been debated as a non-sustainable source of protein, can be replaced with a variety of plant-based ingredients to reduce the cost of fish feed without changing the nutritional profile. Soybean meal, rapeseed meal, cottonseed meal, cassava starch, canola meal, corn gluten meal, and ipil ipil meal are all plant-based ingredients and further studies need to be done to know about their optimum usage in fish feed for various cultured fish species. With proper understanding of the nutritional aspects of a fish species and feed ingredients, it is very much possible to produce a feed which is nutritionally balanced, cost effective, and, at the same time, results in higher growth, better FCR (feed conversion ratio), and is more sustainable for the environment.

             # Aquaculture nutrition # Fish nutrition # Fish Feed

Credit of Writing: Shahid PG student, Faculty of Fisheries, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir and Dr. Mohd Ashraf Rather, Asst. Prof. SKUAST-K