Although all fish examined to date display reduced growth when fed essential amino acid (EAA) deficient diets, Table 1 shows the additional gross anatomical deficiency signs which have been reported under experimental conditions with juvenile fish fed rations deficient in one or more particular EAA's.
|Limiting EAA||Fish species||Deficiency signs1|
|Lysine||Oncorhynchus mykiss||Dorsal/caudal fin erosion (1,2), increased mortality (2)|
|Cyprinus carpio||Increased mortality (3)|
|Methionine||O. mykiss||Cataract (4,5,14)|
|Salmo salar||Cataract (6)|
|Tryptophan||O. mykiss||Scoliosis2 (7–10), lordosis 2 (7,10), renal calcinosis (8), cataract (7,9), caudal fin erosion, decreased carcass lipid content (9); elevated Ca, Mag, Na and K carcass concentration (7)|
|Oncorhynchus nerka||Scoliosis (12,13), cataract (13)3|
|Oncorhynchus keta Oncorhynchus kisutch||Scoliosis (12)|
|Miscellaneous||C. carpio||Increased mortality and incidence of lordosis observed with dietary deficiencies of leucine, isoleucine, lysine, arginine and histidine (3)|
1 1-Walton, Cowey & Adron (1984),
3-Mazid et al. (1978),
4-Walton,Cowey & Adron (1982),
5-Poston et al. (1977),
6-Barash, Poston &Rumsey (1982),
7-Walton et al. (1984),
8-Kloppel & Post (1975),
9-Poston &Rumsey (1983),
10-Shanks, Gahimer & Halver (1962),
11-Halver & Shanks (1960),
12-Akiyama et al. (1985),
13-Akiyama, Mori & Murai (1986),
14-Cowey et el.(1992)
2Curvature of the vertebral column
3 Reported incidence of scoliosis and cataract increased with decreasing andincreasing water temperature, respectively (13)
Under practical farming conditions dietary EAA deficiencies may arise from various routes, including:
Poor feed formulation due to the use of disproportionate amounts of feed proteins with natural specific EAA deficiencies. Table 2 presents the chemical score and limiting EAAs of some selected food proteins available to the fish feed compounder. For the sake of comparison chemical scores have been calculated for individual protein sources with reference to the mean dietary EAA requirements of rainbow trout (O. mykiss) and common carp (C. carpio) as given by Ogino (1980). Compared to fish meal, which has a well balanced EAA profile, the majority of protein sources presented have amino acid imbalances which render them unsuitable as a sole source of dietary protein for fish. For example, the deficiency of methionine in plant proteins, yeast, meat and bone meal, blood meal, and hydrolysed feather meal; the deficiency of lysine in oilseeds, hydrolysed feather meal and algae; the deficiency of threonine in some oilseeds and pulses; and the deficiency of tryptophan in fish silage. It is clear from the above that during feed formulation special care must be given to the choice of feedstuffs used so that the desired overall dietary EAA profile is obtained.
Dietary imbalances may also arise from the presence of disproportionate levels of specific amino acids; including leucine/isoleucine antagonisms, and to a lesser extent arginine/lysine and cystine/methionine antagonisms. For example, blood meal is a rich source of valine, leucine and histidine, but is a very poor source of methionine and isoleucine. However, in view of the antagonistic effect of excess leucine on isoleucine, animals fed high dietary levels of blood meal suffer from an isoleucine deficiency caused by an excess of dietary leucine (Taylor, Cole & Lewis, 1977). Although similar antagonisms have also been reported for cystine/methionine (use of hydrolysed feather meal; Ichhponani & Lodhi, 1976) and arginine/lysine (Harper, Benevenga & Wohlhueter, 1970) in terrestrial farm animals, they have not been reported to occur in fish fed synthetic amino acid diet combinations (Robinson, Wilson & Poe, 1981).
Dietary EAA deficiencies may arise from excessive heat treatment of feed proteins during feed manufacture. For example during fish meal manufacture excessive heat treatment has been shown to markedly reduce protein digestibility and biological value due to the destruction of amino acids by oxidation or through the formation of linkages between individual amino acids which are more resistant to digestion (McCallum & Higgs, 1989; Pike, Andorsdottir & Mundheim, 1990). The free epsilon amino groups of lysine are particularly susceptible to heat damage, forming addition compounds with non-protein molecules (reducing sugars) present in the foodstuff (Cockerell, Francis & Halliday, 1972). In addition to decreased EAA availability, toxic substances such as gizzerosine (2-amino-9-(4-imidazolyl)-7-azanonanoic acid) may also be produced from heat treated fish meals containing free histidine and histamine (Okayaki et al., 1983; Watanabe et al. 1987). Although gizzerosine is reported to cause gizzard erosion (GE) in chicks, toxicological signs of rainbow trout fed comparable heat treated whole fish meals containing high levels of histidine and histamine included decreased stomach wall thickness, pycanosis and necrosis of gastric gland cells (Watanabe et al. 1987).
|Potato protein meal||5||89||125||63*||96||128||120||112||149||74||73||73||118||Met|
|Leaf protein meal||6||84||127||57*||56*||112||120||122||129||71||90||96||141||Cys|
|Bakers dried yeast||4||93||116||63*||85||139||112||91||108||86||106||89||141||Met|
|Whole hen's egg||8||77||125||100||130||132||109||97||98||78||92||96||135||Thr|
|Fish meal (herring)||4||76||127||109||78||117||107||80||95||89||96||111||123||Thr|
|Fish meal (white)||4||81||106||104||93||121||109||81||94||90||94||116||129||Thr|
|Fish protein concentr.||2||83||110||118||63*||127||109||85||103||92||90||95||153||Cys|
|Whole shrimp meal||2||83||97||109||85||112||106||95||105||86||73||134||106||His|
|Meat and bone meal||4||77||128||59*||89||109||113||88||60*||86||100||150||88||Met|
|Poultry byproduct meal||4||76||125||81||141||132||123||80||60*||71||87||134||112||Tyr|
|House fly larvae||12||75||103||72||52*||96||90||128||218||77||127||82||147||Cys|
1 Scores based on comparison with the mean essential amino acid requirements of rainbow trout and common carp (Ogino, 1980). Mean EAA requirement (expressed as% of total EAA) being: threonine 10.6, valine 9.5, methionine 5.4, cystine 2.7, isoleucine 7.5, leucine 13.5, phenylalanine 9.5, tyrosine 6.5, lysine 16.8, histidine 4.8,arginine 11.6 and tryptophan 1.7
2 Source: 1-Kay (1979), 2-Gohl (1980), 3-Bolton & Blair (1977), 4-National Research Council (1983), 5-Tunnel Avebe Starches Ltd (UK), 6-Cowey et al. (1971), 7-Methanobacter methylotrophus Unpublished data, 8-Cowey & Sargent (1972), 9-Connell & Howgate (1959), 10-Jackson, Kerr & Cowey (1984), 11-Tacon, Stafford& Edwards (1983), 12-Spinelli (1980)
* Limiting essential amino acids (present below 30% mean fish requirement)
Dietary EAA deficiencies may arise from the chemical treatment of feed proteins with acids (silage production) or alkalies, due to the loss of free tryptophan and lysine/cystine respectively (Kies, 1981).
Dietary EAA deficiencies may arise from the leaching of free and protein bound amino acids into the water. For example, Grabner, Wieser & Lackner (1981), reported the loss, through leaching, of almost all the free and about one-third of the free plus protein bound amino acids from frozen or freeze-dried zooplankton (Artemia Salina and Moina spp.) after a ten minute immersion period at 9°C. A similar rapid leakage of free amino acids (FAA) has also been observed from frozen Daphnia upon thawing; 23.1% leakage of all FAA during five minutes in water after thawing (Holm & Walther, 1988).
Nutritional pathologies may arise from the consumption of feed proteins containing toxic amino acids or their derivatives. Feed proteins containing toxic amino acids which have been reported to have a negative effect on fish growth and feed efficiency (including eventual fish death) include the plant legumes Leucaena leucocephala (toxic nonprotein amino acid - mimosine; Jackson, Capper & Matty, 1982; Wee & Wang, 1987) and Sesbania grandiflora and Canavalia ensiformis (toxic amino acid - L-canavanine; Martinez-Palacios et al. 1988, Olvera et al. 1988).
In addition to the non-essential amino acids, certain EAA (ie. leucine) have also been reported to exert a toxic effect in fish when present in dietary excesses (Hughes, Rumsey & Nesheim, 1984; Robinson, Poe & Wilson, 1984). For example, the reported toxicity signs for a dietary excess of leucine (13.4% of diet) in rainbow trout (O. mykiss) included scoliosis, deformed opercula, scale deformities, scale loss, and spongiosis of epidermal cells (Choo et al. 1991).