Effects of omnivorous filter‐feeding fish and nutrient enrichment on the plankton community and water transparency of a tropical reservoir

1. The major aim of this study was to test the hypothesis that nutrient enrichment and the introduction of the Nile tilapia (Oreochromis niloticus), an exotic omnivorous filter‐feeding fish, operate interdependently to regulate plankton communities and water transparency of a tropical reservoir in the semi‐arid northeastern Brazil. 2. A field experiment was performed for 5 weeks in 20 enclosures (9.8 m³) to which four treatments were randomly allocated: tilapia addition (F), nutrient addition (N), tilapia and nutrient addition (F + N) and a control treatment with no tilapia or nutrient addition (C). A two‐way repeated measures anova was undertaken to test for time, tilapia and nutrient effects and their interactions on water transparency, total phosphorus and total nitrogen concentrations, phytoplankton biovolume and zooplankton biomass. 3. Nutrient addition had no effect except on rotifer biomass, but there were significant fish effects on the biomass of total zooplankton, copepod nauplii, rotifers, cladocerans and calanoid copepods and on the biovolume of total phytoplankton, large algae (GALD ≥ 50 μm), Bacillariophyta and Zygnemaphyceae and on Secchi depth. In addition, we found significant interaction effects between tilapia and nutrients on Secchi depth and rotifers. Overall, tilapia decreased the biomass of most zooplankton taxa and large algae (diatoms) and decreased water transparency, while nutrient enrichment increased the biomass of rotifers, but only in the absence of tilapia. 4. In conclusion, the influence of fish on the reservoir plankton community and water transparency was significant and even greater than that of nutrient loading. This suggests that biomanipulation of filter‐feeding tilapias may be of importance for water quality management of eutrophic reservoirs in tropical semi‐arid regions.     

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

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.     

Experimental study of the impacts of planktivorous fishes on plankton community and eutrophication of a tropical Brazilian reservoir

We examined the impacts of three facultative planktivorous fishes, Congo tilapia (Tilapia rendalli), bluegill (Lepomis macrochirus) and tambaqui (Colossoma macropomum), and an obligate planktivorous fish, silver carp (Hypophthalmichthys molitrix) on plankton community and water quality of a tropical eutrophic reservoir, Paranoá Reservoir, Brasília, Brazil, conducting both laboratory selective grazing experiments and an enclosure experiment. The first two species inhabit this reservoir and the remaining two are recommended for introduction. The field experiment was performed in ten limnocorrals (2 m³ each) and lasted five weeks. During the enclosure experiment, silver carp suppressed copepod nauplii, cladocerans and rotifers while the presence of tilapia and bluegill were associated with increased rotifers density. The dominant blue-green algae,Cylindrospermopsis raciborskii (98% of phytoplankton biomass) was enhanced in the presence of bluegill, tilapia and tambaqui, but reduced in the presence of silver carp. This impact on plankton is in agreement with the results of the laboratory feeding trials. The observed alterations in water quality parameters in fish limnocorrals are discussed in relation to plankton community and eutrophication of this ecosystem. It is suggested that the control of the undesirable algaeC. raciborskii directly by silver carp grazing is a promising management tool.     

Some aspects of biology and aquaculture potentials of <Emphasis Type="Italic">Tilapia guineensis</Emphasis> (dumeril) in Nigeria

The paper emphasizes on the several attempts made to raise the brackish water tilapia species, Tilapia guineensis both on an experimental and production basis by researchers and fish farmers in Nigeria. Besides, the aquaculture potentials of Tilapia guineensis have been reported by several authors. However, problems exist which are not found with the culture of other tilapia species. Even under most favourable conditions (e.g. the monosex culture of Tilapia guineensis), a poor growth rate and a mediocre feed conversion do not presage profitable aquaculture exploitation. The present review therefore throws light on areas of further research to enhance the growth performance of Tilapia guineensis with emphasis on fish larvae nutrition and first feeding (development of bio-encapsulated feed for larval fish based on nutritionally enriched nematodes and Calanoid copepods), digestibibilty of the feed ingredients, elucidation of the dietary protein requirements, improved culture technique through the use of the Recirculating Aquaculture Systems and the adoption of the most recent technology (The YY Male technology) that produces Genetically Male Tilapia through genetic manipulation. Specific recommended areas for further research are also proffered.     

Responses of phytoplankton to fish predation and nutrient loading in shallow lakes: a pan-European mesocosm experiment

1. The impacts of nutrients (phosphorus and nitrogen) and planktivorous fish on phytoplankton composition and biomass were studied in six shallow, macrophyte‐dominated lakes across Europe using mesocosm experiments. 2. Phytoplankton biomass was more influenced by nutrients than by densities of planktivorous fish. Nutrient addition resulted in increased algal biomass at all locations. In some experiments, a decrease was noted at the highest nutrient loadings, corresponding to added concentrations of 1 mg L^?1 P and 10 mg L^?1 N. 3. Chlorophyll a was a more precise parameter to quantify phytoplankton biomass than algal biovolume, with lower within‐treatment variability. 4. Higher densities of planktivorous fish shifted phytoplankton composition toward smaller algae (GALD < 50 μm). High nutrient loadings selected in favour of chlorophytes and cyanobacteria, while biovolumes of diatoms and dinophytes decreased. High temperatures also may increase the contribution of cyanobacteria to total phytoplankton biovolume in shallow lakes.     

罗非鱼对水质的影响

鱼类是影响水库等水质的重要因素,以我国南方主要养殖鱼类之一的罗非鱼为对象,通过广东大镜山水库原位围隔实验,研究了鱼类对水质的影响。结果表明,与对照组相比罗非鱼围隔中总氮,总磷和叶绿素a浓度分别升高了42%,129%和347%。罗非鱼的排泄增加了水体营养负荷,为浮游植物生长提供大量的营养盐,引起浮游植物生物量增加,水体透明度降低。罗非鱼通过营养盐释放所产生的上行效应明显大于由其牧食导致的下行效应。     

Interactions between Nile tilapia (Oreochromis niloticus) and cladocerans in ponds (Khartoum,Sudan)

Juvenile Nile tilapia (Oreochromis niloticus) are omnivorous, and the question asked in this study is how they affect on their environment? Do they mainly act as predators on the cladoceran zooplankton or do they compete with the cladocerans for phytoplankton? This problem was studied in three ponds with and three ponds without small tilapia (3–5 cm). The fish growth rate, the succession of plankton species and the changes in abiotic conditions, were monitored over a period of 67 days. The fish biomass was kept low and the mean was approximately constant (12.6 g m^?2) during the experiment. Phosphate was added to avoid phytoplankton nutrient limitation. Although the diet of Nile tilapia contained both phytoplankton and zooplankton, the fish affected the ecosystem in a similar way as zooplanktivorous fish. The fish ponds got more phytoplankton due to increase of Chlorophyta. Effects on the other phytoplankton groups Euglenophyta, Bacillariophyta, Cryptophyta and Cyanophyta could not be registered. The ponds without fish had higher densities of Daphnia lumholtzi and D. barbata. The other Cladocerans seemed less influenced by fish presence. The relative fish growth rate was most positively correlated with the density of Daphnia lumholtzi, Diaphanosmoa excisum and Bosmina longirostris. Tilapia seemes to have two feeding modes: (1) preying on large zooplankton and (2) unselective filtration of small planktonic organisms such as phytoplankton. In our experiment the first feeding mode affected the ecosystem more than the second.     

Long Term Effect of Cyprinid Fishes on Phytoplankton and Zooplankton Communities in a Shallow Water Protection Reservoir

The effects of fish kill and different fish stocks on the phytoplankton and zooplankton dynamics were studied in a shallow hypertrophic reservoir system. When fish stock was below 100 kg ha⁻¹, nutrient availability was not the main limiting factor for growth of phytoplankton. Consequently top‐down forces controlled phytoplankton. In the years with high fish stock (>100 kg ha⁻¹) the bottom‐up forces dominated as nutrient availability was the main limiting factor for growth of phytoplankton. We can conclude that significant water quality improvement can be achieved in the reservoir system by decreasing fish stock below 100 kg ha⁻¹. Although clear‐water phase could be stabilised temporary by macrophytes, stabilisation of good water quality requires continuous regulation of fish community. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of a grazing phytoplanktivorous fish and growth enhancement of the grazed alga

Summary The blue tilapia, Tilapia aurea, consumes the green alga, Ankistrodesmus falcatus, with some algal cells passing through the gut in viable condition. Grazing fish grew and the grazed algal populations had enhanced densities compared to ungrazed populations. Algal growth enhancement was not produced by either bacteria or fish excreting an algal limiting nutrient. Possible ingestion and digestion of bacterial cells by the fish might release nutrients to the algal cells that were otherwise unavailable. Blue tilapia may be affecting algal communities in ways other than by passive size selection. Enhancement of algal growth by the blue tilapia could have important implications for understanding the phytoplankton dynamics in waters containing blue tilapia.     

Carbon budgets for a phytoplanktivorous fish fed three different unialgal populations

Summary The filter feeding blue tilapia, Tilapia aurea, was fed three different algae. Blue tilapia ingestion of two green algae, Chlamydomonas sp. and Ankistrodesmus falcatus and the filamentous blue-green alga, Anabaena flos-aquae, ranged from 21%–89% of the available cells. There were significant differences in the assimilation of algal carbon by the fish depending on the alga fed; A. flos-aquae was the easiest to assimilate (83%). The fish respired significantly less of the Chlamydomonas sp. ingested carbon (15%). The gross growth efficiency of fishes fed either green alga was not significantly different (22%–24%), but these efficiencies were significantly less than the gross growth efficiency of fish fed A. flos-aquae (46%). The carbon budgets for fish feeding on the green algae were similar to that constructed from the literature for a congener fed a mixed algae diet. However, the assimilation component of the budget for blue tilapia fed A. flos-aquae was 2 times greater than that of the literature budget.     

Net cages enhance golden mussel (Limnoperna fortunei) larval density and condition factor

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Strong impact of nitrogen loading on submerged macrophytes and algae: a long‐term mesocosm experiment in a shallow Chinese lake

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Mesocosm experiments on nutrient and fish effects on shallow lake food webs in a Mediterranean climate

1. Nutrient and fish manipulations in mesocosms were carried out on food‐web interactions in a Mediterranean shallow lake in south‐east Spain. Nutrients controlled biomass of phytoplankton and periphyton, while zooplankton, regulated by planktivorous fish, influenced the relative percentages of the dominant phytoplankton species. 2. Phytoplankton species diversity decreased with increasing nutrient concentration and planktivorous fish density. Cyanobacteria grew well in both turbid and clear‐water states. 3. Planktivorous fish increased concentrations of soluble reactive phosphorus (SRP). Larger zooplankters (mostly Ceriodaphnia and copepods) were significantly reduced when fish were present, whereas rotifers increased, after fish removal of cyclopoid predators and other filter feeders (cladocerans, nauplii). The greatest biomass and diversity of zooplankton was found at intermediate nutrient levels, in mesocosms without fish and in the presence of macrophytes. 4. Water level decrease improved underwater light conditions and favoured macrophyte persistence. Submerged macrophytes (Chara spp.) outcompeted algae up to an experimental nutrient loading equivalent to added concentrations of 0.06 mg L^?1 PO₄‐P and 0.6 mg L^?1 NO₃‐N, above which an exponential increase in periphyton biomass and algal turbidity caused characean biomass to decline. 5. Declining water levels during summer favoured plant‐associated rotifer species and chroococcal cyanobacteria. High densities of chroococcal cyanobacteria were related to intermediate nutrient enrichment and the presence of small zooplankton taxa, while filamentous cyanobacteria were relatively more abundant in fishless mesocosms, in which Crustacea were more abundant, and favoured by dim underwater light. 6. Benthic macroinvertebrates increased significantly at intermediate nutrient levels but there was no relationship with planktivorous fish density. 7. The thresholds of nutrient loading and in‐lake P required to avoid a turbid state and maintain submerged macrophytes were lower than those reported from temperate shallow lakes. Mediterranean shallow lakes may remain turbid with little control of zooplankton on algal biomass, as observed in tropical and subtropical lakes. Nutrient loading control and macrophyte conservation appear to be especially important in these systems to maintain high water quality.     

Population dynamics, distribution, and growth rate of tilapia (Oreochromis mossambicus) in the Salton Sea, California, with notes on bairdiella (Bairdiella icistia) and orangemouth corvina (Cynoscion xanthulus)

The Salton Sea is a highly saline lake that has long supported sportfishery and large populations of fish-eating birds. A study was initiated in 1999 to assess the status of orangemouth corvina (Cynoscion xanthulus), bairdiella (Bairdiella icistia) and tilapia (Oreochromis mossambicus × O. urolepis). Multimesh (50 × 2 m) gillnets were set at nine stations in 1999, ten stations in 2000 and six stations in 2002. These stations were sampled every two months in 1999, every three months in 2000 and once in 2002. O. mossambicus was the most abundant of the four species, with a maximum mean catch per unit effort (CPUE) 13.8 kg net⁻¹ h⁻¹ or 29.9 fish net⁻¹ h⁻¹ being observed at the river mouth stations in August 1999. From spring to summer, tilapia CPUE increased at nearshore and river mouth stations and decreased at pelagic stations, apparently reflecting migration away from midlake areas in response to anoxia or hypoxia caused by periodic springtime overturn events in deep waters. Tilapia catches in nearshore, river mouth and pelagic habitats were 83 and 60% males in 1999 and 2000, respectively. Tilapia catches in rivers in August 1999 averaged only 6% male. During 1999–2000, the tilapia population consisted essentially of only the 1995 and 2000 year classes. Harsh conditions at the Salton Sea have led to erratic reproduction and survival rates and unstable age structures for its resident fishes. Massive parasite infestations of fry and physiological stressors such as anoxia, high sulfide levels, high salinity and high and low temperatures are potential causes of the irregular recruitment and periodic dieoffs of tilapia. The abundance of all fish species declined over the years of study. Between 1999 and 2002, the late summer mean CPUEs for tilapia, bairdiella and orangemouth corvina at four nearshore stations dropped from 16 fish to 0.02 fish, from 4.7 fish net to 0.23 fish, and from 0.08 fish to 0.02 fish, respectively. During 2000–2003, parallel declines occurred in estimated numbers of adult fish involved in mass mortality events at the Sea. The boom-and-bust dynamics of tilapia and other fish populations in the Sea have major consequences for fish-eating bird populations, for other components of the ecosystem, and for the recreational value of the lake. Guest Editor: John M. Melack Saline Waters and their Biota     

Effects of trophic levels (chlorophyll and phosphorous content) in three different water bodies (urban lake,reservoir and aquaculture facility) on gill morphology of Nile tilapia (Oreochromis niloticus)

Histological and ultrastructural analyses of gills were observed in Nile tilapia collected from three different waterbodies in southeast Brazil: an urban lake in a park in the city of São Paulo, a reservoir in a rural city, and a commercial aquaculture facility. These waterbodies were analyzed and classified as hypereutrophic, eutrophic, and supereutrophic, respectively, with 310.00, 94.00, 28.00 of phosphate ( μg L^?1) and 65.49, 24.95, 12.83 of chlorophyll (μg L^?1). A significant difference in the histological alterations index (HAI) was observed only in fish from the urban lake, with the presence of cell hypertrophy, hyperplasia, aneurism, and other alterations. When compared to the other groups, a large quantity of rodlet cells was also observed in the urban group. These results demonstrate the correlation of eutrophic states of water with gill morphology. Also discussed is the premise that large amounts of organic material dissolved in water can alter the morphology of the fish gills.     

Does high nitrogen loading prevent clear‐water conditions in shallow lakes at moderately high phosphorus concentrations?

1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1⁺ fish (Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m^?2. 2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls. 3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L^?1 and TP >0.13–0.2 mg P L^?1. These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L^?1, irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L^?1. 4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor. 5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re‐establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes.     

Feeding and control of blue-green algal blooms by tilapia (Oreochromis Niloticus)

Outbreak of blue-green algal blooms, with associated unsightly scum and unpleasant odor, occurs frequently in eutrophic lakes. We conducted feeding experiments to study ingestion and digestion of Microcystis aeruginosa by tilapia (Oreochromis niloticus) under laboratory conditions and field testing to reduce Microcystis blooms by stocking tilapia in Lake Yuehu and other eutrophic waters in Ningbo, China between 2000 and 2003. Our results show that tilapia was capable of ingesting and digesting a large quantity of Microcystis. Digestion efficiency ranged from 58.6 to 78.1% at water temperature of 25 °C. Ingestion rate increased with increasing fish weight and water temperature. Intensive blooms occurred in Lake Yuehu in both 1999 and 2000. The lake was stocked with silver carp (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis) and a freshwater mussel (Hyriopsis cumingii) at a total biomass of 9.8 g m⁻³ in early 2001, and tilapia at 3–5 g m⁻³ in April of 2002. From June to October, average phytoplankton density decreased from 897.6×10⁶ cells l⁻¹ in 2000 to 291.7×10⁶ cells l⁻¹ in 2001 and 183.0×10⁶ cells l⁻¹ in 2002. Compared to 2000, the annual average phytoplankton biomass in 2001 and 2002 decreased by 48.6% and 63.8%, respectively. The blue-green algal biomass which made up 70% of the total phytoplankton biomass in 2000 was reduced to 22.1% in 2001 and 11.2% in 2002. Meanwhile, Secchi depth increased from 20–50 cm to 55–137 cm during the same time period. Similar results were observed in some other eutrophic waters. For example, algal bloom disappeared about 20 days after tilapia fingerlings were stocked (8–15 g m⁻³) to a pond in Zhenhai Park. Chlorophyll a concentration and phytoplankton production declined dramatically whereas water transparency increased substantially. However, the impacts of tilapia on nitrogen and phosphorus dynamics in natural lakes need further investigation. Our studies revealed that stocking tilapia is an effective way to control algal blooms in eutrophic waters, especially in lakes where nutrient loading cannot be reduced sufficiently, and where grazing by zooplankton cannot control phytoplankton production effectively.     

Diel changes in the alkaline phosphatase activity of bacteria and phytoplankton in the hypereutrophic Villerest reservoir (Roanne,France)

The diel changes of the size fractioned alkaline phosphatase activity (APA) were studied in relation to several abiotic and biotic factors in Villerest reservoir (located on the Loire river, near the city of Roanne, France), bihourly during two days in July 1992. The APA measured in this work exceeded considerably those reported in the literature, suggesting that dissolved mineral phosphorus was not available to microorganisms. At 1 m, the APA was primarily due to bacteria which actively assimilated organic P compounds released by photosynthetic algal metabolism. At 5, 10 and 20 m, the APA was predominantly algal. The high concentrations in SRP (soluble reactive phosphorus) would indicate that orthophosphates were not bioavailable. The reverse (i. e availability to phytoplankton) would have resulted in undetectable levels of P-PO _inf4 ^sup3– due to the massive proliferation of algae in Villerest reservoir.     

Effects of Nutrients,Fish, Charophytes and Algal Sediment Recruitment on the Phytoplankton Ecology of a Shallow Lake

The influence of nutrient levels, fish density and charophytes on the phytoplankton ecology of a shallow Mediterranean lake was studied by means of an in situ mesocosm experiment. Different levels of nutrients and fish were added over the course of an eight‐week experiment, during which charophytes were removed towards the end. After submerged plants were removed, phytoplankton biomass increased significantly in all the mesocosms, with a reduction of algal diversity and species richness and dominance of cyanobacteria. Cyanobacteria recruited from the sediment played an important role in sustaining planktonic populations of the dominant species. Oscillatorial species (Pseudanabaena galeata, Planktolyngbya limnetica) dominated at higher nutrient levels (0.5–1 mg L^–1 P and 5–10 mg L^–1 N) and chroococcal cyanobacteria (Merismopedia tenuissima) at lower nutrient levels. Density of planktivorous fish had little effect on the algal recruitment from the sediment and phytoplankton biomass and diversity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spatiotemporal dynamics of the spread of African tilapias (Pisces: Oreochromis spp.) into rivers of northeastern Mesoamerica

African tilapias (Oreochromis spp.) occur in more than 100 countries outside of their native ranges and research on their invasions is largely lacking. We investigated spatiotemporal patterns of tilapia spread into 29 drainage basins in Belize and parts of Guatemala and Mexico, drawing on field data and interviews with fishermen. Habitat-suitability models for tilapias were created from geospatial and species occurrence data, and fishermen interviews were used to reconstruct the chronology of tilapia spread into predicted suitable habitats. Tilapia (predominantly Nile tilapia, O. niloticus) presence was confirmed at 78 sites in 9 of 29 drainage basins. Our habitat-suitability model predicted that 7,510 linear km of river habitat in the study area were vulnerable to colonization by tilapias, predominately in mid- to low elevation main stem rivers, from sea level to 277 m above sea level. The reconstructed spatial chronology of spread showed that the invasion started in 1990 and progressed slowly (2 km yr^?1) through an establishment phase before rapid expansion (~30 km yr^?1) between 1996 and 2002, after which new detections slowed. Human movement of fish for aquaculture was identified as a primary cause of dispersal that interacted with flooding as an important secondary cause. The shortest paths across low elevation drainage divides between major basins revealed several potential corridors for future tilapia spread during flooding. Research into tilapia spatial metapopulation structure and economic fisheries status, more stringent regulation of aquaculture activities, pro-active fisheries management, and development of policies to screen potentially invasive species before importation are recommended to avoid additional releases of tilapia and further spread in the region.