The impact of turbidity on the foraging ability and risk taking of two cichlid species

: the invasive Nile tilapia (Oreochromis niloticus) and the threatened Manyara cichlid (Oreochromis amphimelas)

Abstract

Turbid waters are a natural part of productive aquatic habitats. However, turbidity does influence numerous fish behaviours, even when within the range of parameters found naturally. Human development is a major cause of increased turbidity and many agricultural, mining and building projects increase runoff into rivers and sedimentation. Turbidity restricts the visual ability of fish, changing the efficiency of foraging, reproduction and antipredator behaviour. How turbidity influences these reactions depends on the species and the life stage of the fish, further complicating the potential impact turbidity has on aquatic ecosystems. As the initial reaction to many types of environmental change is behavioural, studying how turbidity changes the behaviour of individuals will enable more accurate assessments of the impacts of environmental change on fish populations. To do this we tested the impact of turbidity on the Nile tilapia, Oreochromis niloticus, and the Manyara tilapia, Oreochromis amphimelas. The Nile tilapia is an invasive fish that increases turbidity in areas where the threatened Manyara tilapia resides, potentially contributing to the threatened status of the Manyara tilapia. We tested the impact of turbidity in two experiments that tested the foraging ability, antipredator behaviour and inter-individual consistent behaviours of both species across a range of turbidity. Our results suggest that rising turbidity increases the foraging efficiency of the Nile tilapia but the Manyara tilapia foraged most efficiently at the intermediate level of turbidity. In general, the Nile tilapia consumed more food than the Manyara tilapia. When no food was present, both species displayed increased antipredator behaviour in the higher turbidity as measured by increased shelter use. Neither species showed consistent inter-individual behaviour, i.e. personality, variation. Overall, the results indicate that turbidity is more advantageous for the Nile tilapia and so they are likely to outcompete the Manyara tilapia in turbid habitats.

Date of Award	21 Jan 2021
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Christos C Ioannou (Supervisor) & Sean A Rands (Supervisor)