Abstract

In field populations of the New Zealand crayfish Paranephrops planifrons, growth was faster in pasture streams than native forest streams, possibly due to differences in temperature and diet. Juveniles were collected from native forest and pasture streams and reared in individual chambers for 9 weeks to investigate the effect of temperature and diet on the components of crayfish growth: moult increment and intermoult period. Juveniles were fed leaf detritus (fern and elm) or benthic invertebrates (Chironomus sp.) at two diurnally fluctuating temperatures representative of native forest (12-15°C) and pasture (16-23°C) streams. Survival was low in the leaf detritus treatments at both temperature regimes, and growth rates were significantly lower than for juveniles fed invertebrate food. Growth rates between temperature treatments were not significantly different, but juveniles in the cool treatment had a longer intermoult period. Stable carbon isotopes analysis showed that leaf detritus was not assimilated into crayfish tissue, unlike the chironomid food source that directly contributed to growth. Diet affected both the size increase at moult as well as the frequency of moulting in P. planifrons juveniles, whereas temperature only affected the length of the intermoult period. In field populations of crayfish, temperature is likely to be the primary influence on growth rates unless invertebrate food resources are limited.

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