Responses of seven species of native freshwater fish and a shrimp to low levels of dissolved oxygen

Abstract

The tolerances of seven New Zealand freshwater fish species and one species of shrimp to low levels of dissolved oxygen were determined in the laboratory by holding fish at dissolved oxygen levels of 1, 3, or 5 mg litre‐1 for 48 h at 15°C. Juvenile rainbow trout (Oncorhynchus mykiss) were also tested for comparison. All of the banded kokopu whitebait (Galaxias fasciatus), juvenile torrentfish (Cheimarrichthys fosteri), adult and juvenile common smelt (Retropinna retropinna), juvenile common bully (Gobiomorphus cotidianus), and trout were dead after 48 h exposure to 1 mg litre‐1. Adult and juvenile inanga (Galaxias maculatus), adult common bully (Gobiomorphus cotidianus), and shrimp (Paratya curvirostris) had mortalities ranging from 27 to 80% at 1 mg litre‐1, whereas all of the elvers (Anguilla spp.) survived. Juvenile rainbow trout were the most sensitive of the species tested, and the only species that had mortalities during exposure to 3 mg litre‐1. No deaths of any fish occurred at 5 mg litre‐1. Time to 50% mortality at 1 mg litre‐1 for common smelt (adult and juvenile) and juvenile common bully were similar to those for juvenile rainbow trout. Most fish moved towards the surface within the first few hours of exposure to 1 mg litre‐1. Rainbow trout was the only species that showed consistent surfacing behaviour at 3 mg litre‐1 and rarely were fish observed to move towards the surface at 5 mg litre‐l. Within the limits of the lifestages and species tested, adequate protection is provided for native fish by adopting the United States Environmental Protection Agency dissolved oxygen criteria for salmonid waters.