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Title: Chitinolytic enzymes and bacteria in fish and their role in nutrition
Author: Lindsay, Gabriel Jonathan Homer
ISNI:       0000 0001 3610 5611
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1983
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A study of chitinolytic enzymes and bacteria in rainbow trout Salmo gairdneri and cod Gadus morhua revealed that the enzymes are endogenous and constitutive. Tissues had characteristic levels of chitinase which were of the same order within species. The digestive tract of starved cod was not sterile but contained similar numbers of bacteria to feeding fish. Representative bacterial isolates were purified and studied-in detail. Batches of rainbow trout fed chit in-containing diets (up to 25% chitin) were found to have similar levels of digestive tract chitinolytic enzymes as fish on a chitin-free diet. The effect of chitinous diets on rainbow trout growth suggest that the carbohydrate is a poor energy source that cannot replace starch in commercial salmonid diets. Apart from its minor energy contribution , chitin did not have any fish growth promoting properties. Chitin digestibility in rainbow trout estimated by the chromic oxide internal standard method was low (<10%) although the accuracy of this procedure to determine chitin digestibility in fish was questioned. A study of the early development of gastric chitinase activity in trout revealed that the enzyme could first be detected during the swim-up-stage and reached maximum activity in fry about 50 days after hatching. The distribution of chitinolytic enzymes in the digestive tract of trout and cod revealed a similar pattern. High levels of chitinase were associated with the stomach and chitobiase with the intestine although both enzymes were present to some extent in all parts of the digestive tract. The properties of trout and cod chitinases were investigated using a variety of substrates. Chitinase activity in the trout stomach is sufficiently potent for this to be considered a rich source. A study of the non-digestive tract of rainbow trout revealed that the enzymes are present in most tissues but their function was enigmatic. Seasonal sampling of cod chitinases revealed that enzyme levels were not correlated with the presence of chitin nor was any seasonal trend apparent. A survey of digestive chitinolytic enzymes in North European fish did not show any correlation between enzyme level and feeding habit but the results suggest that the primary function of chitinase in fish may be to disrupt the chitinous exoskeleton of prey in the absence of structures that accomplish this mechanically. A procedure for the large scale culture of the centric diatom Thallassiosira fluviatilis was devised and its extracellular chitin purified in sufficient quantities to allow routine chitinase assay. Electron microscopic studies of the enzyme hydrolysed spines revealed that chitinase hydrolyses only the apices of microfibrils.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry