Abstract:
Possible causes of deaths of Oreochromis niloticus in Lake
Chivero were examined in relation to changes in limnological
conditions monitored over a 25-month period. The
fish deaths coincided with the collapse of an algal bloom
that had developed and builtup in the lake for 8 months.
Chlorophyll a and dissolved oxygen increased to average
concentrations of 42.4 lg l)1 and 10.9 mg l)1 respectively
prior to the collapse of the bloom. Dissolved oxygen
decreased when the bloom started to die off and coincided
with the fish deaths when the average surface dissolved
oxygen concentration in the lake was 3.9 mg l)1 and was
at a depth of 5 m <2 mg l)1. Mortality probably resulted
from depressed oxygen levels caused by the high oxygen
demand from the massive algal die-off and released algal
toxins. This is the first time that die-off of algae has been
linked to fish-kills in Lake Chivero as occurs in other
hypereutrophic systems.