The growth of rainbow trout (Salmo gairdneri) given diets containing chitin and its relationship to chitinolytic enzymes and chitin digestibility

Digestibility of chitin in cod,Gadus morhua, in vivo

“…The apparent indigestibihty of chitin appears contradictory to the very high level of chitinase in the stomach tissue of S. gairdneri, reported previously by Micha et al (1973): in vitro, the stomach mucosa of S. gairdneri released 16290 ~tg NAG x h -1 • g-1 (chitin being used as enzyme substrate). Lindsay et al (1984), conducting very extensive feeding studies with S. gairdneri, confirmed Buddington's result regarding the "hydrolysis resistance" of chitin: The digestibility of chitin, added at 10 and 30 % to the food of S. gairdneri, was determined to be close to zero. Having fed diets containing 4 to 25 % chitin over a 12-week period, the growth of test fish was significantly depressed when compared to control fish which received a mixture containing 25 % starch.…”

“…In high contrast, enzymatic measurements by the same authors revealed that very strong activities of both chitinase and chitobiase of endogenous origin were present in the guts of the rainbow trout. Moreover, Lindsay et al (1984) were able to show that amino-sugars, i.e. end products of chitin degradation, could be utilized as an energy source by the trout.…”

“…In an attempt to explain the fact of very strong chitinolytic potential on one hand, and practically zero digestibility of chitin on the other hand, Lindsay et al {1984} pointed out that fish in nature do not ingest purified chitin; they assumed, chitinase in trout is "nonfunctional" since protein covalenfly bound to chitin and other materials intimately associated with chitin, may present an obstacle to its hydrolysis. (If this assumption is correct, why then were the rainbow trout unable to digest the highly purified chitin, fed with the experimental diet?}…”

“…In contrast to the well documented fact that the guts of many fish constitute a rich source of chitinases, chitin is most often referred to as very poorly digestible or indigestible by fish (RSsch, 1985). Especially in the case of Salmo gairdneri, reports of the very poor digestibility of chitin (Buddington, 1980;Lindsay et al, 1984) seem puzzling since this species has been shown to have strong chitinolytic potential (Jeuniaux, 1963;Micha et al, 1973;Lindsay et al, 1984). This paper describes experiments to determine the digestibihty of natural chitin in cod, Gadus morhua (L.).…”

“…The enzyme produced by chitinolytic bacteria is characteristically different from "fish own" chitinase, for example with regard to the optimum pH-range for its activity (Jeuniaux, 1963;Okutani, 1966;Lindsay et al, 1984;Danulat, 1986a). Considering the extreme abundance and the major contribution of chitin to the diet of many fishes, it is surprising that only a few publications exist on its digestibility in vivo (Geyer, 1940;Mann, 1948;Buddington, 1980;Lindsay et al, 1984). In contrast to the well documented fact that the guts of many fish constitute a rich source of chitinases, chitin is most often referred to as very poorly digestible or indigestible by fish (RSsch, 1985).…”