Tuesday, December 2, 2014

02/12/2014: Algae in ornamental fish feeding

by Dr Aleksandra Kwasniak-Placheta, Tropical, Opolska str. 25, 41-507 Chorzow, Poland
and Prof. Dr Leszek Moscicki, Lublin University of Life Sciences, Doswiadczalna str. 44, 20-280 Lublin, Poland in November-December 2014 International Aquafeed (IAF1406)

The development of aquafeed production is followed by the growing interest in raw materials which are to be interesting, attractive and valuable, not only in terms of their properties. 

There is no doubt that algae are one of them. Feeds with the addition of algae are perceived as premium products. This can result from the fact that algae evoke certain associations with healthy food for humans. Animal food with algae must then trigger the same positive associations. Moreover, specially processed algae or feeds with the addition of algae offered by the producers allowed for keeping popular algae-eating freshwater and marine fish.

Algae used in the production of aquafeed for ornamental fish
It is virtually impossible to provide ornamental fish with algae from their natural environment so aquafeed manufacturers use cultivated algae or algae taken from the wild on an industrial scale. The most popular microalga used for aquafeed production is spirulina (Arthrospira platensis). Its content in aquafeed usually ranges from several to even tens of percent. Its properties are well known among aquarium fish keepers when compared with other species such as Chlorella, Scenedesmus, Laminaria, Ascophyllum, Undaria, Ulva etc “Super Spirulina Forte”, Tropical’s food with 36 per cent share of Arthrospira platensis, has been one of the best-selling fish foods on the market for many years. The changing ornamental fish market and new emerging species of fish and invertebrates made it necessary for us to develop and introduce new foods.

Thus the offer of products for herbivorous and algae-eating fish has been enriched with a new food based on three species of algae: Chlorella vulgaris, Ascophyllum nodosum and Laminaria digitata, the last two referred to as kelp algae. It is available as flakes, granules, adhesive and sinking tablets. It is intended for everyday feeding of herbivorous freshwater and marine fish, for which algae is a valuable dietary component, and as a supplementary food for omnivorous species.

Algae as a source of protein
In farm fish feeding algae are mostly used as an alternative source of protein. In case of aquarium fish they are so much more than the source of protein. They provide other valuable ingredients such as unsaturated fatty acids, carotenoids and dietary fibre, which offer benefits such as health, good overall condition, resistance to diseases and colouration improvement. Algae share in aquafeed can be high as a great number of freshwater and marine fish kept in popular aquaria eat algae in the wild. Alga is a difficult dietary component to be substituted without risk to fish’s health. Despite the fact that various species of algae differ in the content of protein and its composition, it seems that they generally contain all amino acids necessary for fish (Dawczyński et al., 2007). This makes algae an even more valuable component of fish foods compared with other plant materials used as the source of protein.

The nutritional value of protein is determined by two main factors: the quantity of essential amino acids in a given protein together with their relative proportions, and digestibility of the protein ‒ the extent to which amino acids are released and absorbed during digestive processes taking place in the gastrointestinal tract. It is the content of digestive protein that informs us about the quality of a given raw material. Why is the nutritional value of protein so important? To fully exploit the genetic potential of fish of all ages, especially farm-raised. Only an adequate content of highly nutritional protein can ensure proper growth in fish and enables their reproduction. Using poor quality animal protein or replacing animal protein with plant protein such as soya makes it necessary to enrich the feeds with synthetic amino acids, first of all with cysteine, methionine and lysine.

It should be noted, however, that our knowledge on the ornamental fish’s demand for essential amino acids is really poor. Dietary research carried out on farm-raised fish proved that the demand for essential amino acids can vary from one species to another. Hence, for the purpose of ornamental fish feeding it seems important to use high quality protein which provides all essential amino acids. This way one can fulfil dietary needs of a large number of species kept in aquaria (see Table: 1).

Table 1: Average content of protein in algae used for the production of feeds for ornamental fish

Table 2: Chemical analysis of popular species of kelp algae used for ornamental fish feeding 

Arthrospira platensis
Organisms belonging to Arthrospira genus can be found in numerous environments. They have been identified in fresh, salty and brackish waters as well as in soil, sand and even in hot springs. Due to the specific conditions of water bodies from which spirulina are collected, it has also become a dietary component of people living in the vicinity of Lake Chad and Texcoco. Green mats collected and then dried contained almost exclusively cells of Arthrospira platensis or Arthrospira maxima. The formation of these monocultures has been strictly correlated with chemical parameters of water (high salinity and pH level ‒ about 10 pH). These are perfect conditions for the development of spirulina and inhibition of other blue-green algae, which can be dangerous to health and life of humans and animals.
In the beginning the main reason why spirulina gained such interest was its exceptionally high content of protein, which ranged from 62 to 68 per cent. This is an impressive value when compared to meat (15-25 per cent) or soya (35 per cent). Moreover, protein from spirulina turned out to be more valuable than protein from plants, even legumes and only slightly worse than milk or egg protein.

Further tests conducted on spirulina continued to reveal an even greater number of outstanding qualities. It turned out that these tiny, twisted cells are rich in assimilation pigments such as chlorophyll, carotenoids, and phycobiliproteins. Spirulina is a leading source of chlorophyll (1.7 per cent DW) (Chronakis et al., 2000). The bacteriostatic properties of this green pigment and its favourable effects on the human body have been used in cosmetic and pharmaceutical industries.

Spirulina contains about 0.5 per cent of carotenoids (DW), mostly beta-carotene and xanthophylls. The carotenoids are an essential component of fish food, not only for their colour-enhancing properties. Carotenoids play a number of other important roles in fish’s bodies. They stimulate immune system, protect valuable cell components (such as nucleic and fatty acids) from the harmful activity of free radicals, some are the source of Vitamin A, which is beneficial for fish’s growth, they promote maturation and reproduction, and finally protect skin and eggs from UV radiation.

Spirulina also contains other beneficial pigments such as phycobilins. These include blue phycocyanobilin, allophycocyanobilin, and red phycoerythrin. Similar to carotenoids, they are antioxidants. They effectively protect fatty acids and other valuable substances against free radicals.

Apart from these pigments, spirulina contains other active substances such as amino-acids, nucleic acids and linoleic acid Its content of iron, magnesium, calcium, copper, phosphorus, and selenium is also significantly high.
Chlorella vulgaris
Unicellular algae belonging to green algae (Chlorophyta). The most popular species is Chlorella vulgaris, which can be found in fresh waters and moist habitats. Similar to spirulina, Chlorella firstly owed its popularity to the high content of protein, which could be used for human and livestock consumption. Chlorella may contain from 45 to 57 per cent of protein rich in essential amino acids (DW). Moreover, chlorella contains large amounts of provitamin A (just like spirulina), folic acid and iron (Tang and Suter, 2011).

Chlorella is also said to have health-promoting properties owed to natural immune stimulator ‒ beta-1.3-glucan and high concentration of chlorophyll present in its cells. Adding beta-1.3-glucan (responsible for the activation of macrophages) to fish foods increases fish’s natural specific and non-specific immune response (Yaakob et al., 2014). The concentration of chlorophyll in chlorella cells reaches in average about 2 per cent of dry weight, however one may achieve higher concentration of this green pigment by adjusting growing conditions. Chlorophyll facilitates digestion, reduces the number of decay bacteria in the gastrointestinal tract, acts as an antioxidant, helps to detoxicate and when used externally as a bath it supports treating injuries and skin infections (as aquarists claim). Apart from that, it facilitates the regeneration of cells and increases the concentration level of haemoglobin in the blood (Yaakob et al., 2014).

Chlorella vulgaris, similarly to spirulina, is a very rich source of carotenoids. In its dry weight one will find about 0.4 per cent of these pigments, 80 per cent of them in red shades (Gupta et al., 2007). The concentration of carotenoids in chlorella cells can be increased by a strict control of growing conditions. Chlorella is effectively used for the coloration enhancement in koi and goldfish (Gouveia et al., 2003; Gouveia and Rema, 2005).

The role of carotenoids in fish’s bodies is complex and the demand for these pigments is ongoing. Fish cannot synthesise carotenoids de novo, hence one must provide them in food. Colourful species of ornamental fish are particularly demanding. The minimum carotenoid level in fish’s diet ranges from species to species. Coloration improvement in tetras, cichlids, gourami, goldfish and danio has been observed when 30 mg of astaxanthin has been added to one kilo of formulated feed In clownfish (Amphriprion ocellaris, Premnas biaculeatus) coloration enhancement has been visible after a week of providing food with 100 mg/kg astaxanthin. At the same time growth acceleration has been noted (Lorenz and Cysewski, 2000).

Chlorella added to feed for Plecoglossus altivelis reduced the excessive accumulation of fat in tissues. The fats were better utilised, which is probably the result of chlorella affecting the hormone system (lipolytic hormones stimulation) (Gholam et al., 1987). Similar conclusions were reached by Tartiel et al. (2008), who fed Nile tilapia (Oreochromis niloticus) with chlorella. The content of chlorella (not exceeding 50 per cent) accelerated the growth in tilapia, reduced fat in tissues and increased the concentration of protein. These properties of chlorella seem particularly important in case of aquarium fish, who often suffer from fatty degeneration of internal organs caused by overfeeding or poorly balanced feeds for ornamental fish.
Kelp algae
Kelp algae are a mixture of seaweed belonging to green-blue algae, which are rich in minerals, including easily assimilable organic iodine compounds, vitamins, dietary fibre and pigments such as fucoxanthin and chlorophyll. Their addition to the food facilitates digestion and enhances overall condition of fish. Dietary fibre in seaweed may even reach 33 up to 50 per cent of dry weight. It’s far more than in higher plants. Table 2 presents chemical analysis of popular kelp algae used for aqua feed.
There are two types of dietary fibre in the seaweed: insoluble (cellulose, mannan, xylan) and soluble such as alginic acid, fucoidin and laminarin. Dietary fibre performs many physiological functions, for instance it increases intestinal transit time, facilitates the development of valuable intestinal microbial flora, binds bacterial toxins and heavy metal ions. This group of polysaccharides added to aquafeed allows for better food utilization and growth. It also supports detoxication. Even a small addition of Ascophyllum nodosum (5 per cent) improves nutritional value of the food (Yone et al., 1986). However, it should be noted that too high polysaccharide concentration in the diet can deteriorate assimilability of the nutrients. Numerous research proved anti-bacterial and antiviral properties of algin acid, fucoidin and laminarin and their positive effect on immunity (Kraan, 2012).

Macroalgae contain an average of 1-3 per cent of fat, which is relatively small in comparison to microalgae, which can contain even up to 40 per cent. Despite its small amount, the fat from macroalgae is very valuable thanks to Omega-3 acids. The demand for Omega-3 and Omega-6 fatty acids is partly fulfilled by the fish themselves, as they can produce it from HUFAs provided in the food. However, the ability of carnivorous and marine fish to transform HUFAs into Omega-3 and Omega-6 is relatively small, hence one must supplement them additionally with formulated fatty acids.
Seaweed is rich in vitamins A, B1, B2, B3, B9, C and E, macronutrients and trace elements (iodine, iron, potassium, magnesium, calcium, selenium and phosphorus), most of which is in the form of easily assimilable organic compounds. Laminaria digitata contains on average about 4 g of iodine per kg DW. This form of iodine is highly stable. A small L. digitata addition of 0,8 per cent (providing 32 mg iodine/kg of food) into the fish food is enough for the concentration of iodine in fish’s tissues to increase 4 times (Schmid et al., 2003).

Similarly to chlorella, Laminaria digitata facilitated using fat as a source of energy, when added to the diet of Spondyliosoma cantharus and Seriola quinqueradiata, which indicates that one of the seaweed components affects fat metabolism (Nakagawa et al., 1997).

Conclusive remarks
In feeding of ornamental fish microalgae are first of all the sources of easily digestible protein, vitamins, unsaturated fatty acids and natural pigments. Numerous research indicate that the best results are reached when microalgae are added to food, rather than used separately (Sommer et al., 1990). Macroalgae provide primarily macronutrients, trace elements and dietary fibre.

The beneficial effect on the ornamental fish is the result of the combined action of all the ingredients. Alga is not just another interesting and eagerly eaten by the fish ingredient of formulated feeds. Most of all, it is an effective agent to improve fish’s condition. Regular using of feeds with algae ensures intense and bright colours and protects delicate, herbivorous species against digestive disorders.

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