The nutritional value of organic detrital aggregate in the diet of fathead minnows

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1. The nutritional value of detrital aggregate, which refers to the mixture of plant debris (i.e. organic detritus) and microorganisms, in the diets of fathead minnows (Pimephales promelas Rafinesque) was assessed in experiments using surface benthic samples from three sites in Clear Lake (Houghton County, Michigan, U.S.A.). 2. In the first experiment, fish were fed small ( < 250 μm) and large (250-1000 μm) particle detritus from one profundal and two littoral sites. Fish in all treatments lost weight. However, fish fed detritus from the littoral erosional site, where wild fish forage intensively, had significantly lower weight loss. 3. In the second experiment, fish were fed various quantifies of Artemia with or without ad libitum erosional site detritus. Growth was proportional to the mass of Artemia consumed, yet minnows showed increased growth with the detritus supplement at low invertebrate rations. 4. This study shows that detrital aggregate produced by decompositional processes at the erosional site could be nutritionally valuable to minnows. It appears that a feeding strategy of consuming detritus with a higher nutritional quality (i.e. detrital aggregate) as a dietary supplement benefits fishes in temperate as well as tropical systems.

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Freshwater Biology