New Zealand freshwater shrimp
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| Paratya curvirostris (Heller, 1862) |
The New Zealand freshwater shrimp (Kouraura in Māori), Paratya curvirostris, is a shrimp of the family Atyidae found only in slow-flowing streams and rivers in New Zealand.
The New Zealand freshwater shrimp is the only species of freshwater shrimp in New Zealand.
Although it is found throughout New Zealand it is found at lower altitudes in the south suggesting temperature is an important factor limiting its distribution. It is a characteristic occupant of lowland streams, where it is usually found amongst stream margin vegetation and weed beds. Adults may be found down river to brackish water up to around 50% seawater strength.
This species is the only member of its family to exhibit protandry, in which sex is defined by the age and maturity of the individual rather than at development. As all individuals undergo a male phase of development before transforming to adult female forms small females are rare, and almost all large individuals are likely to be female. The eggs of the female are carried under the tail until hatching when the young are then released to float downstream in the current to the sea to develop. It is thought that they inhabit estuaries during their growth phase. These juveniles migrate upstream in late summer and autumn similar to whitebait. Movement is by swimming by flapping movements of the fin-like structures under the abdomen (pleopods) when the water velocity is low, and by walking gripping the substrate with the pincers of their walking legs when the water velocity is higher.
New Zealand freshwater shrimps are detritivores feeding on detritus, algal films on rocks and wood, and on bacteria. These are scraped off and picked up by the 2 pairs of pincers held out front which possess large curved hairs. Larger particles are further fragmented by the mouthparts (maxillipeds).
