Osmoregulation, salinity tolerance and the site of ion excretion in the halobiont chironomid, Tanytarsus barbitarsis Freeman

Abstract

The ability of T. barbitarsis to survive in hypersaline waters is examined. Osmoregulation and salinity tolerance of Port Augusta specimens and the site of ion excretion in larva and pupa are investigated. Results show that the haemolymph of T. barbitarsis is approximately isosmotic with media of 0.3 osmol kg^-1, but is maintained hyperosmotic in media of lower concentration and hyposmotic in more concentrated media. The LC₅₀ is found to be 89 ± 5 g I^-1. As in the Culicidae, fourth-instar larvae of T. barbitarsis employ the posterior rectal tissue to excrete chloride ions. However, in the pupa, which has no flux of water through its gut, the site is on the dorsum of the thorax.