Nutritional Significance of Facultative Detritivory to the Juvenile White Sucker (Catostomus commetsoni)

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Abstract
The nutritional significance of detritus in the diet of the juvenile white sucker (Catostomus commersoni) was evaluated by experiments designed to assess assimilation efficiency and growth of sucker fed detritus and other foods. Sucker in laboratory aquaria assimilated detritus with the following efficiencies: dry mass = 19.6%, ash-1 free dry mass (AFDM) = 59.7%, total amino acids = 68.9%, energy = 69.4%. Assimilation efficiencies calculated for invertebrates and natural field diets were slightly higher. Diatom assimilation was low (5.5%). In growth experiments, sucker fed detritus ad libitum lost weight, while those fed Artemia ad libitum grew rapidly. However, detritus increased the growth rate of sucker fed a limited inverebrate ration and reduced the rate of weight loss relative to unfed fish. The ratio of digestible protein to digestible energy calculated for natural detritus diets (3.2 mg amino acid/kj) indicates that the protein content of detritus is too low to support growth. Detritus provides energy which complements limited invertebrate protein to enhance growth or reduce the rate of weight loss when invertebrate prey are not available.