The chironomid larvae are widely recognized as an important food for many fish and cultured invertebrates, such as crustaceans (Armitage, 1995; Tidwell et al., 1997). This food, used in vivo, in frozen and in dry, is an excellent source of protein, lipid, vitamins and minerals (e.g., Czeczuga & Gierasimow, 1973; De La Noűe & Choubert, 1985; Habib et al., 1997, Bogut et al., 2007, Kara, 2013). This food is characterized by the relatively high protein content (up to 56%), the high digestibility (De La Noűe & Choubert, 1985) and the high energy content.

Crude protein, fat, water, ash, dry matter, essential amino acids and fatty acids are analyzed from freshly collected Chironomus plumosus larvae in order to evaluate their suitability as the components for farmed fish diet (Bogut et al., 2007). Crude protein content are 7,6 % and 55,7 % in fresh larvae and dry matter, respectively, being adequate for growth needs of all freshwater fish sorts and categories. Phenylalanine (2,76 % of dry weight), leucine (2,49 %) and lysine (2,48 %) are most abandant among essential amino acids. In sum, essential amino acids in C. plumosus larvae are present in quantities adequate for feeding majority of omnivorous and carnivorous freshwater fish species (Bogut et al., 2007).

The content of free amino acids in larvae of C. annularius is studied by Czeczuga & Gierasimow (1973). Aspartic acid is found in the largest amounts, 6,17 g % of dry mass, the next are such amino acids as glutamic acid (5,04 g %), leucine together with isoleucine (4,86 %) and alanine (4,58 g %). Habib et al. (1997) have studied 14 species of chironomid larvae, with the dominance of Chironomus javanus, grown in algal culture, Chlorella vulgaris. Glutamic acid (9,44 % of total acids), aspartic acid, glycine and alanine are most abundant than other amino acids.

In C. plumosus, crude fat content are 1,3 % and 9,7 % in fresh larvae and dry matter, respectively, being energetically sufficient for all warm water living fish (Bogut et al., 2007).  The crude fat contains 26,12 % saturated, 30,42 % monounsaturated and 34.03 % polyunsaturated fatty acids. In general, chironomid larvae contain more amounts of unsaturated fatty acids (Habib et al., 1997) that is needed for normal growth of freshwater fish and prawn fry.

Basic References

Armitage P.D. 1995. Chironomidae as food. The Chironomidae: biology and ecology of non-biting midges. Armitage P.D., Cranston P.S., Pinder L.C.V. (Editors.). Chapman and Hall, London, 423-435

Bogut I., Has-Schon E., Adamek Z., Rajković V., Galović D. 2007. Chironomus plumosus larvae as suitable nutrient for freshwater farmed fish. Poljoprivreda 13, 159-162

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Zooplankton

The amino acid content in freshwater copepods (Eudiaptomus zachariasi), cladocerans Daphnia pulex and Ceriodaphnia sp. as well as copepodites (Cyclops strenuus) is studied by Dabrowski & Rusiecki (1983). Yet, the amino acid content in saltwater brine shrimp, Artemia salina, nauplii on hatching and during fasting is determined.

The major free amino acids in C. strenuus dry matter are 1,43 % arginine, 0,22 % histidine, 0,20 % alanine, 0,15 % glutamic acid and 0,11% lysine. Free arginine content decreases in the daphnids as they increase in the size. The content of all free amino acids in fasting Artemia nauplii is lower than in the freshwater zooplankters. The major free amino acids in nauplii are 0.55 % proline, 0.41 % alanine, 0.34 % glycine and 0.37 % serine, respectively.

Chemical composition of Daphnia longispina and other daphnids is studied by Holm & Walther (1988). Non-polar amino acid alanine ((from 13,4 mol % to 20,3 mol %), basic amino acids arginine (11,6 mol %) and lysine (10,2 mol %) as well as polar, uncharged amino acid glycine (10,0 mol %) are most abundant in the plankton extract.

The same authors have demonstrated rapid leakage of amino acids from frozen daphnids upon thawing.

The moisture content, crude protein level and amino acid profile of three freshwater zooplankton (Moina micrura, Diaphanosoma excisum, Brachionus calyciflorus) commonly used for rearing fish larvae are analyzed by Ovie & Ovie (2006). The moisture contents and crude protein levels are similar, as follows: M. micrura 89,0 % and 52,4 %; D. excisum 89,3 % and 57,3 %; B. calyciflorus 91,6 % and 50,3 %, respectively. The samples are represented by 17 amino acids: nine essential and eight non-essential amino acids. The dominant essential amino acids (per 16 g N) in M. micrura are lysine (10.73 g), arginine (8,17 g) and leucine (8,0 g); in D. excisum lysine (9,95 g), leucine (8,0 g) and valine (6,23 g); in B. calyciflorus leucine (8,95 g), lysine (8,64 g) and arginine (6,37 g). According to Ovie & Ovie (2006), in all three species tested (M. micrura, D. excisum, B. calyciflorus), glutamine and aspartic acid dominate the non-essential amino acid profile.

Seasonal Variations

Seasonal variations in the concentrations of 19 free amino acids in the whole body homogenates of freshwater amphipod Gammarus pseudolimnaeus are measured by Graney & Giesy (1986). The greatest total concentrations of free amino acids, 226,9 and 286,4 nmol per mg dry weight, are observed in April and May, with declining through summer months. The pattern of relative concentrations of individual free amino acids in G. pseudolimnaeus is found to be similar to that of other freshwater invertebrates. Alanine represents the most abundant amino acid (16,2-22,4 %) throughout an entire year. Arginine and leucine exhibit the next greatest abundances and comprised an average of 10,2 and 10,4 % of the total free amino acid concentration, respectively.

Holm & Walther (1988) give seasonal variations in the concentrations of free amino acids in D. longispina and other daphnids.

Amino acid profile of amphipod Gammarus lacustris in the beginning of autumn has the high level of alanine (22,6 mmol per ml of homogenate) and ornithine (17,6 mmol) (Karanova & Andreev, 2010). The amount of alanine and ornithine accounts for 39,8 % of the total pool of free amino acids, taken together alanine, ornithine, lysine and leucine form 55% of this pool.

Decapoda

The abdominal muscle, antennal gland, haemolymph, hepatopancreas and ovary of freshwater Astacus leptodactylus are analysed for free and protein-bound amino acids by van Marrewijk & Ravestein (1974). Free amino acid content is highest in the abdominal muscle and lowest in the haemolymph. The most abundant free amino acids are glycine, arginine and alanine. Together they account for up to 38 mol % in the hepatopancreas and up to 73 mol % in the abdominal muscle of the total amount. The content of free amino acids in the hemolymph of three crayfish species, Astacus astacus, A. leptodactylus and Ortonectes limosus, is researched by Rogala et al. (1978), setting the differences in lysine and histidine content.

In freshwater Chinese mitten crab, Eriocheir sinensis, and A. astacus concentration of amino acids is less than in marine decapods (Camien et al., 1951) (mitten crab is an invasive species that lives in freshwater but migrates seawards to breed).