Long-term study of growth in the New Zealand flatworm Arthurdendyus triangulatus under laboratory conditions

In a 1-year laboratory study of the New Zealand flatworm Arthurdendyus triangulatus, individual growth, degrowth and regrowth were manipulated via the feeding regime, with the compost worm Eisenia fetida as prey. A mean growth rate of 25 mg live weight wk^—1 was evident, individual rates ranging between 18 and 38 mg wk^?1. Degrowth was associated with egg capsule deposition for which the maximum rate was 0.5 capsules wk^?1. The more egg capsules produced, the greater the adult weight loss, degrowth rates ranging from 8 to 55 mg wk^?1. Change in flatworm body weight (gain/loss) also correlated with the length of the food introduction interval, though weight could be maintained for circa 2 weeks. Weight loss was not simply a function of hunger, voluntary cessation of feeding (possibly related to egg capsule production) being a confounding factor. During the growth phase, individual predation rate ranged from 0.9 to 1.1 earthworms wk^?1, rate of tissue consumption ranging from 346 to 485 mg wk^?1. Conversion efficiencies of earthworm to flatworm tissue were estimated to range between 3.8% and 10.7%. The impact of this exotic planarian on earthworm populations is discussed.