THE NUTRITIONAL-VALUE OF ORGANIC DETRITAL AGGREGATE IN THE DIET OF FATHEAD MINNOWS

1. The nutritional value of detrital aggregate, which refers to the mi xture of plant debris (i.e. organic detritus) and microorganisms, in t he diets of fathead minnows (Pimephales promelas Rafinesque) was asses sed in experiments using surface benthic samples from three sites in C lear Lake (Houghton County, Michigan, U.S.A.). 2. In the first experim ent, fish were fed. small (<250 mu m) and large (250-1000 mu m) partic le detritus from one profundal and two littoral sites. Fish in all tre atments lost weight. However, fish fed detritus from the littoral eros ional site, where wild fish forage intensively, had significantly lowe r weight loss. 3. In the second experiment, fish were fed various quan tities of Artemia with or without ad libitum erosional site detritus. Growth was proportional to the mass of Artemia consumed, yet minnows s howed increased growth with the detritus supplement at low invertebrat e rations. 4. This study shows that detrital aggregate produced by dec ompositional processes at the erosional site could be nutritionally va luable to minnows. It appears that a feeding strategy of consuming det ritus with a higher nutritional quality (i.e. detrital aggregate) as a dietary supplement benefits fishes in temperate as well as tropical s ystems.