Invasive Tilapia Research Articles

Genetic and morphological characterization of invasive tilapia in Morocco confirm the presence of two feral species Oreochromis niloticus (Linnaeus, 1758) and Oreochromis aureus (Steindachner, 1864) and their hybrids

Genetic and morphological characterization of invasive tilapia in Morocco confirm the presence of two feral species Oreochromis niloticus (Linnaeus, 1758) and Oreochromis aureus (Steindachner, 1864) and their hybrids

Community structure of indigenous fishes relative to habitat variation and invasive tilapia in lakes of Quintana Roo, Mexico

Community structure of indigenous fishes relative to habitat variation and invasive tilapia in lakes of Quintana Roo, Mexico

Diet-habitat ecology of invasive tilapia and native fish in a tropical river catchment following a tilapia invasion

Many species of tilapia (a collection of fish species from the cichlidae family) have biological traits that make them successful invaders. Widespread herbivory has been observed across tilapia species, however knowledge on habitat preferences and tilapia interactions with native fish food webs is limited. This study was conducted three years after spotted (Pelmatolapia mariae) and Mozambique (Oreochromis mossambicus) tilapia were detected in the Mitchell River catchment, northern Australia. Tilapia diet and habitat preferences and their trophic position in native fish food webs was determined using a combination of stomach content, stable isotope, and habitat assessment analyses. Plant material was the most abundant item in tilapia stomachs, and some stomachs also contained other items in small quantities, such as fish eggs, small shrimp, and bivalves. Some niche overlap occurred between P. mariae and native omnivore or herbivore fish species. Macrohabitat type (in-channel (no tilapia), floodplain (no tilapia), weir (tilapia present)) was related to native fish food web structure, with weir food webs showing similarities to floodplain food webs. Floodplain habitats including creeks and wetlands were also most similar to weir habitats and may therefore be most at risk of colonization as tilapia spread throughout the catchment. This study clearly demonstrated that the successful rapid invasion of these two tilapia species is linked to suitable habitat with abundant food that fuels growth and reproduction. These findings increase understanding of diet related habitat use during new tilapia invasions and trophic interactions with native species.

The Distribution of Invasive Tilapia Throughout A Tropical Man-Made Lake With Special Reference to Temengor Reservoir, Malaysia

With a surface area of 15, 200 ha, the Temengor Reservoir, in the northwestern state of Perak was selected among other lakes in Malaysia for the development of a large tilapia aquaculture facility in 2008 due to its favourable environmental conditions. Tilapia has never been recorded at Temengor Reservoir prior to the establishment of this facility. However, preliminary observations in a previous study detected tilapia species in the natural waters of this lake, strongly suggesting these were escapees from the floating cages which had invaded the natural waters. Following that, a study was conducted to assess the distribution of these escapees throughout the Temengor Reservoir. The cultured tilapias are easily recognizable with elongated mouth and body, and long caudal fin. The sampling was conducted using gill nets. The distribution of the escaped tilapia throughout the Temengor Reservoir was mapped based on previous data and current data on the fish checklist conducted at different sampling points of this lake, and the occurrence (presence/absence) of escaped tilapia was recorded. A comparative analysis was conducted at several number of points among three sampling areas, according to the radii from the fish cage facility; <5km (S1), 5-15km (S2), and >15km (S3). The ANOVA showed significant differences (p<0.05) in Catch per Unit Effort (CPUE) weight between the three sampling areas. As tilapia is a highly successful global invasive species, the presence of tilapia at these and other locations at Temengor Reservoir should be rigorously monitored. Complete eradication of tilapia in the lake is of high urgency. We recommend intensive targeted fishing of the species in the vicinity of the cages and biological control by native predators to preserve and conserve the native fish species at Temengor Reservoir.

Assessing freshwater fish biodiversity of Kumbe River, Papua (Indonesia) through environmental DNA metabarcoding

Context The ability to accurately assess biodiversity is a critical first step towards effective conservation and management. However, assessment of biodiversity using conventional monitoring programs is often constrained by high cost and a lack of taxonomic expertise. Environmental DNA (eDNA) metabarcoding may be a useful tool to efficiently catalogue biodiversity in areas that cannot be easily assessed using other methods. Aims Here, we evaluated the potential of eDNA metabarcoding for assessing fish biodiversity and distribution in the Kumbe River, Papua Province, Indonesia. Methods We selected four sampling locations and collected seven eDNA samples from each location. We used eDNA metabarcoding of the Cytochrome-b gene to characterise the fish community. Key results A total of 23 species were detected, three of which comprised 92% of sequence reads detected: Melanotaenia goldiei (32%), Craterocephalus randi (31%), and the invasive tilapia Oreochromis niloticus (29%). Only five species that were previously detected using conventional methods were detected by metabarcoding: M. goldiei, Craterocephalus stercusmuscarum, O. niloticus, Neoarius graeffei, and Arius arius. We detected 18 species (70% native) that have never been recorded from the Kumbe River. Conclusions This work has demonstrated that fish biodiversity is substantially underestimated in the Kumbe River. Environmental DNA metabarcoding is a promising rapid, non-invasive and cost-effective method for assessing fish biodiversity in Papua. Implications The findings support future investment in eDNA metabarcoding to characterise the fish biodiversity in Papua. This will assist in allocating the limited resources for conservation and management to areas most at risk from anthropogenic impacts.

Community Structure of Indigenous Fishes Relative to Invasive Tilapia and Habitat Variation in Lakes of Quintana Roo, Mexico

Community Structure of Indigenous Fishes Relative to Invasive Tilapia and Habitat Variation in Lakes of Quintana Roo, Mexico

State of aquatic invasive species in tropical India: An overview

Abstract India, a megadiverse tropical country is grappling with the rising trend of aquatic invasions. Out of 532 introduced non-native fish, 16 species of freshwater aquaculture and aquarium were assessed invasive by using a risk assessment protocol, ‘Fish Invasiveness Screening Test’. Six major identified invasion pathways of the aquatic invasive species were inadvertent or deliberate releases, escapes, contaminants from hatcheries, river corridors, stowaways and unaided introductions. Invasion mechanism further elucidated the factors promoting successful invasion in freshwater ecosystems. For predictive future performance of invasive fish, the concrete and predictive values based on mean abundance by weight was calculated. Over 28.67% and 29.02 % persistent increased yield of the invasive Tilapia and Common Carp respectively was predicted in the Ganga river in the coming decades. Single species Tilapia invasion facilitated multiple species fish invasion, manifesting in invasion meltdown. The trophic changes due to fish invasion exhibited biotic homogenization with trophic downgrading. Aquatic invasive species were found highly competitive interacting with native species causing serious biodiversity loss, health hazards, and economic damage consequently affecting the ecosystem services. In spite of available regulatory approaches and guidelines to manage aquatic invasive species, fish invasion has been on the rise. This paper suggests modifications and stringent implementation of the existing regulatory mechanisms besides adopting linkages, cutting-edge research on invasion science and modern molecular containment tools for effective management.

Optimizing the impacts of an invasive species on the threatened endemic biota of a remote RAMSAR site: Tilapia (Oreochromis niloticus) in Lake Kutubu, Papua New Guinea

Sometime between 2010 and 2012, Nile Tilapia (Oreochromis niloticus) invaded the remote Lake Kutubu, in the Southern Highlands of Papua New Guinea, apparently as a result of flooded aquaculture ponds. The subsequent burgeoning population of Tilapia has had apparent impacts on the RAMSAR-listed lakes’ ecology, but paradoxically may be benefiting endemic fish and crustaceans in the lake that have been under severe threat of extinction due to sustenance overfishing. Here, we explore options for eradicating or adaptively managing the invasive Tilapia population, and conclude that it is logistically and socially feasible to use low-risk genetic (chromosomal) technology to establish a non-self-sustaining population in the lake as an alternative protein source for local communities that causes minimal environmental damage while reducing exploitation rates on endemic taxa that have already driven at least three to apparent extinction.

Parasites of the invasive tilapia Oreochromis mossambicus: evidence for co-introduction

Reduced parasite species diversity and infection intensity on invasive populations can facilitate establishment and spread of invasive species. We investigated the parasite diversity of invasive populations of tilapia Oreochromis mossambicus from published literature and necropsies conducted on 72 fish captured in the Ross River, north Queensland, Australia. The parasite diversity of invasive O. mossambicus from 13 countries was compared to published reports on endemic populations in African river systems and tributaries to determine parasite species that had likely been co-introduced. In total, four parasite species were shared between native and invasive tilapia. We propose that these parasites (three monogeneans, Cichlidogyrus tilapiae Paperna, 1960, Cichlidogyrus sclerosus Paperna and Thurston, 1969, Cichlidogyrus halli (Price and Kirk, 1967) and one trichodinid Trichodina heterodentata Duncan, 1977) have likely been co-introduced with invasive Oreochromis mossambicus populations. Invasive Australian O. mossambicus had substantially reduced parasite diversity (five species) compared to cumulative parasite species diversity documented from the native region (23 species). Australian O. mossambicus were infected by two co-introduced parasites and three additional parasite species that have not been recorded previously on this species in Africa indicating possible parasite spillback from Australian natives or alternatively, acquisition from other introduced fauna. The substantially reduced parasite diversity on invasive Australian O. mossambicus could contribute to the ability of this species to become a serious fish pest.

Losing cichlid fish biodiversity: genetic and morphological homogenization of tilapia following colonization by introduced species

Among the many negative impacts of invasive species, hybridization with indigenous species has increasingly become recognized as a major issue. However, relatively few studies have characterized the phenotypic outcomes of hybridization following biological invasions. Here we investigate the genetic and morphological consequences of stocking invasive tilapia species in two water bodies in central Tanzania. We sampled individuals from the Mindu Reservoir on the Ruvu river system, and at Kidatu on the Great Ruaha–Rufiji river system. We screened individuals at 16 microsatellite loci, and quantified morphology using geometric morphometrics and linear measurements. In both the Mindu and Kidatu systems, we identified evidence of hybridization between indigenous Wami tilapia (Oreochromis urolepis) and the introduced Nile tilapia (Oreochromis niloticus) or blue-spotted tilapia (Oreochromis leucostictus). At both sites, purebred individuals could largely be separated using geometric morphometric variables, with hybrids occupying a broad morphospace among the parental species. Our data demonstrate that the gene pools and phenotypic identity of the indigenous O. urolepis have been severely impacted by the stocking of the invasive species. Given the lack of evidence for clear commercial benefits from stocking invasive tilapia species in waters already populated by indigenous congenerics, we suggest further spread of introduced species should be undertaken with considerable caution.

Temperature effects on the distribution of two invasive tilapia species (Tilapia zillii and Oreochromis niloticus) in the rivers of South China

Competitive interactions not only exist between invasive and native fish species but also between different invasive species, especially between those that have broad niche overlap. Nile tilapia (Oreochromis niloticus) and Redbelly tilapia (Tilapia zillii) are the most common invasive tilapia species in the rivers of South China. There may be specific factors that influence their competitive interactions and disturbance patterns, and temperature has been considered the most important factor. To study how temperature affects the distribution patterns and competitive interactions of these two invasive tilapia species, field surveys and laboratory experiments were conducted. Field surveys showed that latitude affected the ratio but not the biomass of all tilapia species. Nile tilapia was more abundant in the southern (warmer) sites, and Redbelly tilapia was more abundant in the northern (colder) sites. The distribution patterns of the two tilapia species were also related to latitude and minimum winter temperature. The results of the laboratory-based temperature experiments further confirmed that Redbelly tilapia can tolerate lower temperatures than Nile tilapia. However, the Nile tilapia were larger in field surveys, and laboratory experiments also showed that Nile tilapia are stronger competitors in warmer water because of their larger body size. Therefore, we suggest that the distribution patterns of these two invasive tilapia species were related to temperature conditions.

Identification of wild tilapia species in the main rivers of south China using mitochondrial control region sequence and morphology

Tilapias are now the most common alien fish in the rivers of South China and the dominant species in many sites. However, wild tilapia species have not been well-characterized or studied systematically. In this study, mitochondrial DNA control regions (mtDNA CR) and morphological characteristics were used to identify invasive tilapia species. Using mtDNA CR sequence, we identified Oreochromis niloticus, Tilapia zillii, Oreochromis aureus, Sarotherodon galilaeus, and hybrids of Oreochromis mossambicus and O. niloticus in the rivers of South China, and characterized their morphological features. Of the 5 species, O. niloticus and T. zillii were the most abundant in the rivers of South China. Furthermore, the distribution of O. niloticus may be related to their large numbers in the aquaculture industry, and the explosion of T. zillii invasion may be related to their strong capacity for environmental adaptation. These findings are beneficial for identifying wild tilapia populations and for the specific control of invasive tilapia species.

Multiple records of aquatic alien and invasive species in diets of native predators in Singapore

We report for the first time the diversity of known aquatic alien species in the diets of four piscivorous predators in Singapore through a review of published and unpublished studies, and our empirical data. Of 15 aliens identified to the species level, 11 were fish, including the highly invasive tilapia (Oreochromis mossambicus [Peters, 1852]). Other alien species include the abundant red-eared slider (Trachemys scripta elegans [Wied-Neuweid, 1839]) and the American bullfrog (Lithobates catesbeiana [Shaw, 1802]). We hypothesize that the diversity of established alien species in Singapore’s aquatic habitats allows for novel ecological interactions, one of which is predation by native species. Our study provides preliminary evidence that alien and invasive species may benefit some native piscivores as a source of prey although it is not possible to infer relative composition of these alien species given our limited data. Future studies should investigate the ecological dynamics of these interactions, including the relative importance of these alien prey to diets and survival of predators.

Reproductive strategies of two invasive tilapia species Oreochromis mossambicus and Tilapia mariae in northern Australia

The reproductive biology of two invasive tilapia species, Oreochromis mossambicus and Tilapia mariae, resident in freshwater habitats in north-eastern Australia was investigated. Oreochromis mossambicus exhibited plasticity in some of its life-history characteristics that enhanced its ability to occupy a range of habitats. These included a shallow, weed-choked, freshwater coastal drain that was subject to temperature and dissolved oxygen extremes and water-level fluctuations to cooler, relatively high-altitude impoundments. Adaptations to harsher conditions included a decreased total length (L(T) ) and age (A) at 50% maturity (m50), short somatic growth intervals, early maturation and higher relative fecundities. Potential fecundity in both species was relatively low, but parental care ensured high survival rates of both eggs and larvae. No significant difference in the relative fecundity of T. mariae populations in a large impoundment and a coastal river was found, but there were significant differences in relative fecundities between several of the O. mossambicus populations sampled. Total length (L(T) ) and age at 50% maturity of O. mossambicus populations varied considerably depending on habitat. The L(Tm50) and A(m50) values for male and female O. mossambicus in a large impoundment were considerably greater than for those resident in a small coastal drain. Monthly gonad developmental stages and gonado-somatic indices suggested that in coastal areas, spawning of O. mossambicus and T. mariae occurred throughout most of the year while in cooler, high-altitude impoundments, spawning peaked in the warmer, summer months. The contribution these reproductive characteristics make to the success of both species as colonizers is discussed in the context of future control and management options for tilapia incursions in Australia.

An evaluation of electrofishing as a control measure for an invasive tilapia (Oreochromis mossambicus) population in northern Australia

Combating the spread of invasive fish is problematic, with eradication rarely possible and control options varying enormously in their effectiveness. In two small impoundments in north-eastern Australia, an electrofishing removal program was conducted to control an invasive tilapia population. We hypothesised that electrofishing would reduce the population density of Oreochromis mossambicus (Mozambique tilapia), to limit the risk of downstream spread into areas of high conservation value. We sampled by electrofishing monthly for 33 months. Over this period, there was an 87% decline in catch per unit effort (CPUE) of mature fish, coupled with a corresponding increase of 366% in the number of juveniles, suggesting a density-dependent response in the stock–recruitment relationship for the population. Temperature was inversely related to CPUE (r = 0.43, lag = 10 days), implying greater electrofishing efficiency in cooler months. The reduction in breeding stock is likely to reduce the risk of spread and render the population vulnerable to other control measures such as netting and/or biological control. Importantly, the current study suggests routine electrofishing may be a useful control tool for invasive fish in small impoundments when the use of more destructive techniques, such as piscicides, is untenable.

Making the Most of Fish Farms

M aking the M ost of F ish F arms B S J Julian Zhu When most people hear the word ‘fish,’ they think of food. In 2009, the Food and Agriculture Organization (FAO) of the United Nations reported world consumption of fish at 117.8 million tons, up more than fifteen million from 2004 (FAO, 2009). Fish, to all but the most dedicated ichthyologist, are represented primarily by dish, taste, and breed: salmon, Atlantic cod, tuna, and the like. However, the prospects of fish as a means of feeding a growing world population are beginning to look more and more perilous. By now, most educated citizens have some idea of the devastation overfishing has caused on wild fish stocks. Overfishing – or harvesting more fish than natural reproduction can sustain – has been prevalent on a global scale for decades, but only recently has the collapse of fish stocks worldwide drawn widespread political attention. Aquaculture – the farming of marine species (primarily fish, but also crustaceans, sea plants, and other marine Figure 1. Nile tilapia, a popular aquaculture fish breed. organisms) – offers a possible alternative to traditional capture, one that could not only ease the burden on wild fish populations, but play a significant role in feeding a growing world population. Despite its promise, however, aquaculture in its current state is far from the perfect solution to providing fish to the world both sustainably and economically. The environmental impact of fish farms as well as the pitfalls of economic inefficiency demand that aquaculture be inspected with a discerning and skeptical eye. Aquaculture on an industrial scale is still a relatively new phenomenon, and monitoring its impacts – both the obvious and hidden – is a responsibility that both potential fish-farmers and policymakers ought to assume. Different fish species are chosen for aquaculture for a variety of reasons, from taste and economic value to hardiness and ease of growth. Of fish species, tilapia is rising as a strong contender for the title of the most popular and aquaculture-viable strain (Bradford, 2011). Similarities in taste and texture between tilapia and Atlantic cod – one of the most popular and heavily overfished fish species “Aquaculture offers a possible alternative to [...] capture” consumed today – make tilapia meat a viable substitute for the overfished cod in most cases, and is therefore growing in market value. More critically, however, tilapia is both hardy and easy to grow, with a flexible diet and relatively high tolerance to environmental factors such as salinity and temperature. That said, the very qualities that make tilapia such a highly valued aquaculture fish make it an extremely potent invasive species. High rates of reproduction and growth, paired with a tolerance to everything but the lowest temperatures, make Mozambique tilapia – the most common strain of farmed tilapia found today – dangerous invaders in tropical and subtropical environments; additionally, tilapia exhibit strong parental care that includes housing young in the parent’s mouth, granting tilapia spawn a far greater range of mobility than that of other fish breeds (Costa-Pierce, 2003). Due to these factors, invasive tilapia have already penetrated ecosystems in Florida, California, and elsewhere, outcompeting native species and presented a serious threat to native biodiversity. For this reason, fish farmers in the United States are seeking to replace the Mozambique strain with Nile tilapia, an easier-to-raise, less aggressively invasive variety. Furthermore, genetic manipulation of aquaculture species targets the precise traits that make fish strains better invaders: increased growth rate, size, and reproductive ability. In addition to threatening ecosystems, aquaculture also raises a significant question about its economic efficiency. If aquaculture is to be marketed as the sustainable 1 • B erkeley S cientific J ournal • S cience of F ood • V olume 16 • I ssue 1

Genetic structure and gene flow in an endangered native tilapia fish (Oreochromis esculentus) compared to invasive Nile tilapia (Oreochromis niloticus) in Yala swamp, East Africa

The introduction of invasive Nile tilapia (Oreochromis niloticus), and the rapacious predator Nile perch (Lates niloticus), into Lake Victoria resulted in a decline in population sizes, genetic diversity and even extirpation of native species which were previously the mainstay of local fisheries. However, remnant populations of native fish species, including tilapia, still persist in satellite lakes around Lake Victoria where they may coexist with O. niloticus. In this study we assessed population genetic structure, diversity, and integrity of the native critically endangered Singidia tilapia (O. esculentus) in its refugial populations in the Yala swamp, Kenya, and contrasted this diversity with populations of the invasive tilapia O. niloticus in satellite lakes (Kanyaboli, Namboyo and Sare) and Lake Victoria. Based on mtDNA control region sequences and eight nuclear microsatellite loci, we did not detect any mtDNA introgression between the native and the invasive species in Lakes Kanyaboli and Namboyo, but did find low levels of nuclear admixture, primarily from O. niloticus to O. esculentus. Some genetic signal of O. esculentus in O. niloticus was found in Lake Sare, where O. esculentus is not found, suggesting it has recently been extirpated by the O. niloticus invasion. In both species, populations in the satellite lakes are significantly genetically isolated from each other, with private mtDNA haplotypes and microsatellite alleles. For O. niloticus, genetic diversity in satellite lakes was similar to that found in Lake Victoria. Our data imply a low frequency of immigration exchange between the two populations of O. esculentus and we suggest that the populations of this endangered species and important fisheries resource should be conserved separately in Lakes Kanyaboli and Namboyo and with high priority.

Invasive tilapia juveniles are associated with degraded river habitats

Abstract Invasions are a main concern for conservationists. Identification of causes that raise or promote an invader's success is one of the first steps for preventing and/or fighting against invasions. In the Brazilian River Paraiba do Sul, juveniles of invasive tilapia Oreochromis niloticus were detected associated with degraded habitats (mainly pollution from various sources). The relative abundance of juveniles of the competitor native species pearl cichlid Geophagus brasiliensis, morphologically and ecologically very similar, was negatively associated with habitat degradation. A species‐specific molecular marker was employed to permit unambiguous identification of these small juveniles (2–3 cm long), which represent the most vulnerable life stage of both species. It is suggested that adaptation to degraded habitats is one of the characteristics of invasive species, and consequently habitat conservation and restoration may help to prevent fish invasions. Copyright © 2008 John Wiley & Sons, Ltd.