Consumption and apparent dry matter digestibility of aquatic macrophytes by male and female crayfish ( Orconectes virilis)

Abstract

Crayfish are generally thought to be omnivores; however, the relative nutritional importance of various foods is poorly understood. In this study, we fed adult (mean weight 18.3 g) male and female crayfish ( Orconectes virilis) 14 aquatic macrophytes and quantified consumption and apparent dry matter digestibility (ADMD). Specifically, we fed cattail ( Typha sp.), horsetail ( Equisetum sp.), bulrush ( Scirpus sp.), arrowhead ( Sagittaria sp.), horned pondweed ( Zannechellia palustris), musk-grass ( Chara sp.), curlyleaf pondweed ( Potamogeton crispus), sago pondweed ( P. pectinatus), American pondweed ( P. nodosus), eel grass ( Vallisneria sp.), water buttercup ( Ranunculus longirostris), water stargrass ( Heteranthera dubia), American lotus ( Nelumbo lutea) and dried, pelleted duckweed ( Lemna sp.). Except for consumption of horned pondweed, there were no significant differences in consumption or ADMD between males and females. Based on the low consumption estimates (ranging from 0.01 to 0.87% body weight/day; overall mean of palatable macrophytes 0.19% body weight/day), it appears that macrophytes do not comprise a major source of nutrients for this size and species. Further, ADMD coefficients were significantly different between macrophytes of similar nutritional composition and may indicate the presence of antinutritional factors. Thus, growth of certain macrophytes in aquaculture ponds should be discouraged, while others may be beneficial as a minor food source or as a source of selected nutrients. Methods for future digestion studies were evaluated and discussed.