Contribution of omnivorous tilapia to eutrophication of a shallow tropical reservoir: evidence from a fish kill

Abstract

SUMMARY 1. We examined whether a large stock of tilapia (>750 kg ha−1, in littoral areas >1300 kg ha−1), mostly Oreochromis niloticus (L.) and Tilapia rendalli (Boulenger), could contribute to the eutrophication of a tropical reservoir (Lago Paranoá, Brasília, Brazil) by enhancing P‐loading. 2. We took advantage of an extensive fish kill (>150 tons removed) during May–August 1997 in a hypereutrophic branch of the reservoir to compare water quality characteristics 1 year before and after this event by means of BACI statistics. We also measured P‐excretion rates in laboratory trials to assess the P‐loading of the reservoir by the tilapia relative to tributary inputs and loading from a sewage treatment plant. 3. Concentrations of chlorophyll a (decline from 84 to 56 μg L−1, P=0.018) and total P (decline from 100 to 66 μg L−1, P < 0.001) decreased significantly in the branch of the reservoir affected by the fish kill, compared with a similar but unaffected branch that served as a control. Because P‐loading by both a sewage treatment plant and tributaries remained high after the incidence, the fish kill was likely to contribute to the observed water quality improvement. 4. Removing 150 tons of dead tilapia corresponded to 20 days of external total phosphorus load (TP‐load) to the branch, and resulted in a reduction of 5.1 kg P day−1 in internal recycling via tilapia excretion, which is equivalent to 12% of the external TP‐load. 5. Implementing professional tilapia cast‐net fisheries could be an efficient biomanipulation approach to improve water quality and limit the occurrence of cyanobacteria blooms and fish kills in hypereutrophic branches of Lago Paranoá and similar tropical lakes.

Estudo da dieta natural de peixes no reservatório de Ribeirão das Lajes, Rio de Janeiro, Brasil

“…Ressalta-se o consumo de colônias de Microcystis sp. verificado para essa espécie, o que já foi observado em ambientes eutrofizados, em que T. rendalli tem apresentado extrema abundância e persistente dominância (Starling et al, 2002). Como o ambiente aquático em questão não apresenta abundância de Microcystis (Huszar et al, 2003), pode ser sugerido que a mesma foi incorporada à dieta por meio de concentração pela filtração de material planctônico pelos rastros branquiais.…”

Composition of the ichthyofauna in Brazilian semiarid reservoirs

“…Oreochromis niloticus, popularly known as "Nile tilapia", is an exotic species that is well established in the Brazilian semiarid region and the most abundant species recorded in Epitácio Pessoa and Argemiro de Figueiredo Reservoirs. This species feeds mainly on phytoplankton and zooplankton, and it has great trophic plasticity and it is highly tolerant to environmental variations (Gurgel & Fernando 1994, Starling et al 2002, Attayde et al 2007). The abundance of Oreochromis niloticus is related to breeding in tanks from Argemiro Figueiredo Reservoir where 406 out of 473 specimens were collected.…”

Electrophysiological assessment of spectral sensitivity in adult Nile tilapia Oreochromis niloticus: evidence for violet sensitivity

“…The optical properties of the water will also vary considerably on a temporal scale, especially during the wet season when influxes of suspended particles from runoff change the water colour and increase levels of turbidity (Bowmaker, 1995). Nile tilapia have a major influence on their underwater light environment as they can contribute to sustaining eutrophication by enhancing nutrient cycling (Starling et al, 2002) through phosphorus excretion and phosphorus release from sediments disturbed during foraging and nest building. The sensitivity to long wavelengths is probably an adaptation to the predominant wavelengths of light in such habitats.…”