UMT MOOC: Ornamental Fish Culture - Topic 4: Nutrition of Ornamental Fish - Protein and Amino Acids; Lipids and Fatty Acids

Protein and Amino Acids
Protein consists of one or more complex molecules consists of chains of amino acid. Elements within a amino acid contains of carbon, hydrogen, oxygen, and nitrogen. Different proteins serves different purpose for any living cells like enzymes or antibody. Amino acids are divided into two categories of indispensable and dispensable. The former category cannot be synthesized and must be obtained externally from diet. The dispensable amino acids can be produced to enable the synthesis. Below are the list of amino acids within the two groups:

(1) Indispensable: Arginine, Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Trytophan, Valine
(2) Dispensable: Alanine, Asparagine, Glutamic acid, Glycine, Aspartic acid, Serine

Having the right protein source for ornamental fishes ensures optimum weight growth and gonadal (sex gland) maturity. However, protein metabolism also leads to ammonia residues which can pollute the aquarium water. The table below (Source: Sales, James & Janssens, Geert. (2003). Nutrient requirements of ornamental fish – A review) shows protein requirements for popular ornamental fish species.

What type of diet should be fed to obtain optimum feed conversion ratio and efficiency. The diet should be at least 45% protein and 6% lipid (more on this later) level. However, over feeding may lead to excessive nutrients which restrict protein intake and growth (this was written in the slide but not from any research literature). Soy bean (for example, tofu) could works as alternative protein source. Some Betta fish breeders we have talked to use tofu as main protein source instead of Dalphia or Blood worm.

Lipids and Fatty Acids
Lipid is a substance that is insoluble in water and an essential component in living cells. Several classes of lipid are fats (stored unused energy), oils, waxes, and phospholipids. Lipids provides energy and essential fatty acids as well as serves as structural components and carriers.

As fish survive in low temperature environment, it needs more long chain fatty acids (LCFAs), which have = >12 carbons to support its cell membrane flexibility. In general for freshwater fishes, two types of fatty acids are needed, either one or both. These are (1) Linoleic acid (18:2n-6) and (2) Linolenic acid (18:3n-3). Both can be found in most vegetable oils.

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