Benthic nutrient cycling: The role of fish in nitrogen and phosphorus regeneration in the rocky littoral zone of Lake Malawi/Nyasa/Niassa, Africa
The interaction between the cichlid fishes of the nearshore rocky littoral zone of Lake Malawi with the epilithic periphyton community is addressed in this study, looking specifically at fish grazing rates and importance of the fish community in recycling of nitrogen and phosphorus through excretion, defecation and mortality.
To determine rates of nitrogen and phosphorus regeneration through excretion and
defecation, a series of in situ fish incubations in 13L plexiglas chambers were
performed at two islands of Lake Malawi. Fish grazing rates were assessed by
determination of fish consumption rates using Kraft's (1992) bioenergetics model
where defecation and excretion rates were derived from the in situ experiments
and growth rates were determined in the lab by rearing 30 fish specimens for 22
days under controlled conditions. Mortality was assessed by the assumption that
it is equal to growth as fishing is negligible and there is no long-term fish
biomass change in the nearshore rocky littoral zone of Lake Malawi.