Algal Quality Controls the Distribution, Behavior and Growth of Algivorous Cichlids in Lake Tanganyika

The nutritional value of primary producer is dependent on the concentrations of C, N and P. These elements are the building blocks for protein, carbohydrates, lipids, nucleic acids and other biochemical compounds. The balance between the supply of dietary elements and the herbivore\u27s demand is crucial for the growth of algivorous organisms, including fish. However, anthropogenic changes in primary producer quality due to sediments may alter the value and quantity of food in the littoral zone of Lake Tanganyika, which may affect both herbivorous near shore and pelagic fisheries. This dissertation focuses on the influence of algae food on herbivore fish. First, I explored the influence of algal quality and quantity on fish growth rates. I fed fish food with different phosphorus concentrations at high and low ration. I found that the growth rate of T.moorii was strongly influenced by the combination of food quality and quantity only when fish were fed good quality food. Lower food quality reduced specific growth rates. When fish are fed poor food, there was no compensation by simply increasing the quantity. I also examined how algal quality and quantity varies among site, and how fish changes their feeding behavior based of food availability. I found that herbivore can potentially practice selective feeding, physiological and morphological adaptations in order to adjust to differences food quality and quantity. Lastly, I examined the relationship between algal resources, fish density and condition factor among and within sites along depth gradient from 1 to 8 m. I found that within sites, fish density, periphyton quality and quantity all decreased with depth, a pattern consistent with fish maximizing energy and nutrient input by aggregating in shallow areas. Among sites, the distribution of algivores was positively correlated with food quality and negatively correlated with algal biomass, patterns that indicate a strong bottom-up and top-down effects of fish on algae