Impact of introduced Nile tilapia (Oreochromis niloticus) on non-native aquatic ecosystems

Comparison of Environmental DNA Metabarcoding and a Traditional Survey Method for Assessing Fish Diversity and Distribution Along Salinity Gradient in an Urban Brackish Reservoir, China

With the decrease in fish diversity, the monitoring of fish has become a current research hotspot. Here, the fish diversity and spatial distribution along a salinity gradient (0.28‱-3.32‱) in Xinglinwan Reservoir, China, were investigated using eDNA and the TSM. With the combination of both methods, 12 species from 6 orders, 9 families, and 11 genera were observed. The invasive species Oreochromis niloticus had the highest relative abundance, accounting for 56.91% in the TSM and 89.80% in eDNA, respectively. eDNA detected 83.33% of the species detected using the TSM, and an additional six species (50.0% of the total species) were detected via only eDNA. Moreover, eDNA supplemented the unavailable abundance data from the TSM. The TSM revealed that the diversity and relative abundance of fish inhabiting seawater and brackish water increased with an increase in salinity, but this was not found using eDNA. Thus, our study highlights that Xinglinwan Reservoir has a low species richness and is suffering from the great harm of ecological invasion. Our findings also show that eDNA could be reliable for providing a comprehensive picture of fish, but discriminating the spatial heterogeneity of fish communities is a challenge for its widespread adoption in lentic brackish systems.

Sustainable Ecosystem Management Strategies for Tackling the Invasion of Blackchin Tilapia (Sarotherodon melanotheron) in Thailand: Guidelines and Considerations

The invasion of blackchin tilapia in Thailand is a critical ecological threat affecting native biodiversity and destabilizing ecosystems. It is also resulting in significant ecological and socio-economic impacts. Originally from West Africa and introduced globally for aquaculture, blackchin tilapia thrive in Thailand's brackish and freshwater ecosystems because of their high reproductive rates, environmental adaptability, and trophic plasticity. This review evaluates potential solutions for the invasion of blackchin tilapia in Thailand from a scientific perspective. The successful invasion of blackchin tilapia in Thailand can be attributed to several key factors, including late detection of the species, the delayed government response, the absence of effective management strategies, and the species' high invasive potential. Given its wide distribution, large population size, and high reproductive rate, the eradication of the entire blackchin tilapia population is unlikely. Management efforts should focus on containment and impact reduction. Early detection and monitoring at the invasion front remain crucial to limit the species' spread. Developing an online platform for tracking invasive species would aid these efforts. Public education and outreach are essential for promoting responsible behaviors for preventing further spread. Encouraging the utilization of blackchin tilapia as a food source and for commercial purposes could help suppress its population while supporting local economies. Biological control and other potentially harmful strategies should be avoided unless supported by strong scientific evidence to ensure minimal risks to ecosystems. Scientific research into controlling blackchin tilapia should be encouraged to develop suitable strategies, including using sterile triploid tilapia. The "polluter pays" policy should be implemented to cover the costs associated with invasive species. Coordinated efforts between researchers, policymakers, and the public are crucial for formulating effective management strategies to promote a balance between economic benefits and long-term environmental sustainability.

Impacts of tilapia aquaculture on native fish diversity at an ecologically important reservoir

Background

The Temengor Reservoir is the second largest reservoir in Peninsular Malaysia. Located in the northwestern state of Perak, it was selected to develop a large-scale tilapia (Oreochromis niloticus) aquaculture facility within the Aquaculture Industrial Zone (AIZ) in 2008 due to its favourable environmental conditions. No record of tilapia has ever been reported in the natural waters prior to this. However, a post-establishment study recorded tilapia sightings in the natural waters of this lake. The cultured tilapia was easily recognizable with the elongated mouth and body, and long caudal fin. It is postulated that these were escapees from the floating cages that had invaded the natural waters and would negatively impact the native fish species. To test our hypothesis, we investigated the impact of the aquaculture facility on native fish diversity through a spatial design.

Methods

The study was focused on assessing the impact of tilapia culture at sites nearer to the AIZ vs more distant sites, the former with a greater likelihood of receiving escapees. Two major sites were chosen; within 5 km (near-cage) and within 5-15 km (far-cage) radii from the AIZ. Fish sampling was conducted using multiple mesh sizes of gill nets (3.7, 5.1, 6.5, 7.6, and 10.2 cm) deployed at the littoral zone of the sampling points. Species diversity, abundance, dietary habits, and habitat preference were investigated.

Results

The CPUE (individual/hour) of native fish species at the far-cage site of the AIZ Reservoir was found to be significantly higher (p < 0.05) than that at the near-cage site. Principal component analysis (PCA) based on diet and habitat preferences showed that the tilapia, O. niloticus had almost overlapping diet resources and habitat with native fish species.

Conclusion

We conclude that there is a correlation between the reduced catches of native species (based on CPUE) and the high presence of tilapia. Thus, appropriate actions must be implemented for strategic and effective planning in terms of native fish conservation.

On the Species Identification of Two Non-Native Tilapia Species, Including the First Record of a Feral Population of Oreochromis aureus (Steindachner, 1864) in South Korea

Tilapia is an invasive species that has become widely distributed around the world. In Korea, introduced tilapia into its aquatic ecosystem for the first time with a species from Thailand in 1955, and later additionally introduced two more species from Japan and Taiwan, thus securing a total of three species of tilapia (O. niloticus, O. mossambicus and O. aureus) as food resources. Since then, O. niloticus has been reported to inhabit certain streams with thermal effluent outlets. Morphological species identification is very difficult for tilapia and a combined analysis of morphological and molecular-based species identification is therefore necessary. This study investigated a tilapia population that inhabits a thermal effluent stream (Dalseo Stream) in Daegu Metropolitan City, Korea, in order to conduct a morphological and genetic species identification of this population. In total, 37 tilapia individuals were sampled. The results of the morphological and genetic species identification analyses found that two species, O. aureus and O. niloticus, inhabit the Dalseo Stream. In Korea, the habitat of the O. niloticus natural population has been reported, but the O. aureus natural population has not been reported. Thus, we observed for the first time that a new invasive species, O. aureus, inhabits a stream in Korea. They are known to cause disturbances to aquatic organisms (e.g., fish, aquatic insects, plankton, aquatic plants) and the habitat environment (e.g., water quality, bottom structure). Accordingly, it is important to study the ecological effects of O. aureus and O. niloticus on the corresponding freshwater ecosystem closely and to prepare a management plan to prevent the spread of these species, as they are notoriously invasive.

DNA barcoding detects resurrected taxon Giuris laglaizei (Sauvage 1880) in Sulawesi, Indonesia: Bolano Sau Lake payangka phylogeny, phenotypic characters and implications for Giuris spp. conservation

Background: The freshwater ichthyofauna of Wallacea is diverse and understudied. A baseline survey of Bolano Sau Lake in Parigi Moutong District, Central Sulawesi Province, Indonesia in 2019 found an eleotrid goby (local name payangka) with characters conforming to the genus Giuris, long considered monophyletic as G. margaritacea/G. margaritaceus but recently found to comprise at least eight species. This study focused on the molecular (DNA barcoding) identification and phenotypic characters of the payangka. Methods: Payangka samples were collected from August to December 2019 in collaboration with local fishermen, weighed and measured, and preserved in 75% ethanol. Length, weight, sex (n=111) and seventeen morphometric characters/six meristic counts (n=42) were recorded. DNA barcoding was performed on a fin clipping preserved in 96% ethanol. Homologous nucleotide sequences were obtained from public (GenBank and BOLD) databases, analysis conducted in MEGA X, and phylogenetic trees edited in the Interactive Tree of Life (iToL). Results: Within the polyphyletic Giuris clade, the payangka sequence resolved into a sub-clade identified as Giuris laglaizei (Sauvage 1880), a recently resurrected taxon, based on a sequence provided by Philippe Keith. The length-weight relationship (L = 0.0087∙W3.162) indicated mildly allometric positive growth. Size distribution differed significantly between male and female fish with significantly larger mean size of males (13.56 cm) than females (11.62 cm). The meristic formula was: D VI-I,8 A I,8 P 13 V I,5 C15. Phylogenic analysis indicated four Giuris species in wetlands around Tomini Bay and five in Sulawesi. Conclusions: This first record of G. laglaizei in Indonesia advances knowledge of Wallacean and Indo-Pacific gobioid biogeography and highlights the need for a revision of the conservation status of the taxa currently grouped under Giuris margaritacea/G. margaritaceus in the IUCN Red List and FishBase databases. The data will inform biodiversity and fisheries management at local and regional levels.

DNA barcoding detects resurrected taxon Giuris laglaizei (Sauvage 1880) in Sulawesi, Indonesia: Bolano Sau Lake payangka phylogeny, phenotypic characters and implications for Giuris spp. conservation

Background: The freshwater ichthyofauna of Wallacea is diverse and understudied. A baseline survey of Bolano Sau Lake in Parigi Moutong District, Central Sulawesi Province, Indonesia in 2019 found an eleotrid goby (local name payangka) with characters conforming to the genus Giuris, long considered monophyletic as G. margaritacea/G. margaritaceus but recently found to comprise at least eight species. This study focused on the molecular (DNA barcoding) identification and phenotypic characters of the payangka. Methods: Payangka samples were collected from August to December 2019 in collaboration with local fishermen, weighed and measured, and preserved in 75% ethanol. Length, weight, sex (n=111) and 17 morphometric characters/six meristic counts (n=42) were recorded. DNA barcoding was performed on a fin clipping preserved in 96% ethanol. Homologous nucleotide sequences were obtained from public (GenBank and BOLD) databases, analysis conducted in MEGA X, and phylogenetic trees edited in the Interactive Tree of Life (iToL). Results: Within the deeply divided Giuris clade, the payangka sequence resolved into a sub-clade identified as Giuris laglaizei (Sauvage 1880), a recently resurrected taxon, based on a sequence provided by Philippe Keith. The length-weight relationship (L = 0.0087∙W3.162) indicated mildly allometric positive growth. Size distribution differed significantly between male and female fish with significantly larger mean size of males (13.56 cm) than females (11.62 cm). The meristic formula was: D VI-I,8 A I,8 P 13 V I,5 C15. Phylogenetic analysis indicated four Giuris species in wetlands around Tomini Bay and five in Sulawesi. Conclusions: This first record of G. laglaizei in Indonesia advances knowledge of Wallacean and Indo-Pacific Gobiiformes biogeography and highlights the need for a revision of the conservation status of the taxa currently grouped under Giuris margaritacea/G. margaritaceus in the IUCN Red List and FishBase databases. The data will inform biodiversity and fisheries management at local and regional levels.

Preliminary study on the toxicological response of red tilapia (Oreochromis niloticus) on landfill leachate treated with Tin(IV) chloride and Jatropha curcas

This study was conducted to evaluate the effect of the toxicity levels of the coagulation and flocculation process on raw and treated leachate using acute toxicity tests. Tin tetrachloride (SnCl₄ ) and the Jatropha curcas (JC) seed were used as coagulant and coagulant aid to remove concentrated suspended solids, SS (534 mg/L), color (19,297 Pt-Co), and chemical oxygen demand (COD) (4188 mg/L) in a stabilized landfill leachate. The toxicity effects on local red tilapia fish (Oreochromis niloticus) were investigated, which involved three main steps, namely, acclimatization, range-finding test, and short-term definitive test. The presence of JC seed (0.9 g/L) as a flocculant reduced the dosage of SnCl₄ from 11.1 to 8.5 g/L and exhibited good removals of 99.78%, 98.53%, and 74.29%, respectively, for SS, color, and COD. The toxicity test indicated that only five fish died in the first 12 h for the treated sample compared with seven deaths for untreated leachate. In 96 h, a total of 42 and 31 mortality rates were noted for the raw and treated leachate samples, respectively. The treated sample could reduce the toxicity effects to the tested tilapia fish and is safe to be discharged at appropriate dilution concentrations. PRACTITIONER POINTS: Coagulation-flocculation by Tin (IV) chloride and Jatropha Curcas (JC) was investigated. Almost complete reduction of SS was obtained at 8.5 g/L of SnCl4 and 0.9 g/L of JC as flocculant. The toxicity effect was evaluated using red tilapia (Oreochromis niloticus) fish as the indicator. Treated leachate was considered acceptable as the number of dead fish was lower than the untreated leachate.

Invasion Risk and Potential Impact of Alien Freshwater Fishes on Native Counterparts in Klang Valley, Malaysia

Simple Summary

The mechanisms on how alien species naturally affect the native species in the real aquatic environment are infrequently studied. This study explores the potential effects of alien fishes on the native fish community, well-being, and trophic preferences in selected rivers of Klang Valley, Malaysia. We found that alien fishes benefited from the impacts of anthropogenic activities in their surrounding habitats, while their plasticity in feeding habits might help them to invade, survive, and dominate. This study revealed the natural mechanisms on the establishment of alien fish species and their potential ecological impacts on native fishes in the rivers of Klang Valley, Malaysia.

Abstract

This study explores the potential effects of alien fishes on the native fish community, well-being, and tropic preferences in selected rivers of Klang Valley, Malaysia. Following the Aquatic Species Invasiveness Screening Kit assessment, most of the alien fishes (80%) are invasive. The alien species occurrences correlated positively (p < 0.05) with poor water quality, such as rivers with high ammonia-nitrogen and nitrite, but negatively with phosphate and dissolved oxygen. Anthropogenic characteristics, such as rivers with high pollution levels and ease of accessibility to the fish habitat, are mainly associated positively (p < 0.05) with the occurrences of alien fish species. In general, the results of fish stomach contents analyses and their associated indices, together with stable carbon and nitrogen isotopes, revealed domination by alien fishes or diet overlaps between both alien and native fish species. This finding indicates that alien fishes benefited from the impacts of the anthropogenic activities in their surrounding habitats, while their plasticity in feeding habits might help them to invade, survive, and dominate in the rivers of Klang Valley, Malaysia.

Inventory of the fish fauna from Laranjinha River, Paranapanema River system, Brazil

Abstract: This work is the most comprehensive survey of the Laranjinha River´s fishes, a tributary of the Cinzas River, Paranapanema River basin. Throughout its course, there is only a low-height dam, including a transposition system located 98 km from its mouth. The sampling was carried out in nine locations, from the source to the mouth, with six field incursions in each location, using different fishing gear. A total of 11,924 fish were collected, distributed in seven orders, 27 families, and 100 species. The most representative order in the number of species was Siluriformes, followed by Characiformes. As for the families, Loricariidae comprised 21% and Characidae 14% of species richness. Phalloceros harpagos was the species with the highest absolute abundance, representing 11.3% of the total, followed by Hypostomus ancistroides with 9.8%. However, considering the average abundance and frequency of occurrence, Hypostomus ancistroides was the most abundant species, followed by Hypostomus cf. paulinus, Psalidodon aff. paranae and Phalloceros harpagos. Among the collected species, the Apteronotus acidops, Brycon orbygnianus, Brycon nattereri, Crenicichla jupiaensis, and Rhinelepis aspera were classified as endangered on the most recent IUCN Red List. Also, from the total sampled fish, 9.8% are considered non-native species. Among the native species recorded, 10 species are large migratory species, which indicates that the Laranjinha River is a route for spawning and maintenance of species diversity in the middle Paranapanema River. Therefore, the Laranjinha River is a heritage of fish diversity and deserves special attention in its preservation.

Foraging behavior interactions between the invasive Nile Tilapia (Cichliformes: Cichlidae) and three large native predators

ABSTRACT The predator-prey relationships between juvenile Nile Tilapia Oreochromis niloticus and native fish species of the Paraná River basin, Brazil, were experimentally examined. Juveniles of O. niloticus were offered to three native predator species (Salminus brasiliensis, Pseudoplatystoma corruscans, and Brycon orbignyanus) in 2,000-L tanks with four levels of habitat complexity (0%, 50%, 100% and RD (rocks and driftwood)). Predator efficiency was more variable among species (S. brasiliensis consumed 86.6% of the prey, P. corruscans 22.5% and B. orbignyanus 18.3%) than among levels of habitat complexity, and S. brasiliensis was faster than the others in detecting and consuming the prey. The higher predatory efficiency observed for S. brasiliensis can be partially explained by its more aggressive behavior (it fed earlier and for longer) and its presence in the surface layer. Here, the presence of predators led to O. niloticus juveniles spending more time at the surface or remaining in schools to coexist at the bottom with the predators, as expected for cichlids under predatory pressure in natural environments. Our results suggest that preserving and restoring populations of S. brasiliensis (and also to some extent P. corruscans and B. orbignyanus) might help to control O. niloticus in the Paraná River basin.

DENSIDADE PLANCTÔNICA DO POLICULTIVO DE Litopenaeus vannamei E Oreochromis niloticus

Resumo Um experimento foi realizado durante 95 dias para avaliar as densidades planctônicas do policultivo do camarão branco Litopenaeus vannamei e da tilápia do Nilo Oreochromis niloticus. O delineamento experimental foi inteiramente casualizado com seis tratamentos e quatro repetições cada. Os tratamentos foram: monocultivo com 10 camarões m2 (10S:0T); policultivo com 10 camarões e 0,5 tilápia m2 (10S:0.5T); policultivo com 10 camarões e 1 tilapia m2 (10S:1T); monocultivo com 2 tilápias m2 (2T:0S); policultivo com 2 tilápias e 2,5 camarões m2 (2T:2,5S); e policultivo com 2 tilápias e 5 camarões m2 (2T:5S). Não foi realizada troca de água e nem fornecimento de aeração artificial durante o período experimental, apenas utilizou-se água para completar o volume perdido pela evaporação. O fitoplâncton variou de 78.981 a 303.260 cél.mL-1 e o zooplâncton variou de 470 a 1.421 org.L-1. Os grupos mais frequentes foram Bacillariophyta (fitoplâncton) e Rotífera (zooplâncton). Pode-se concluir que em sistema de policultivo do camarão branco (Litopenaeus vannamei) e a tilápia do Nilo (Oreochromis niloticus) não ocorrem modificações significativas nas densidades do fitoplâncton e zooplâncton em decorrência da alteração das densidades de estocagem do cultivo.

Metacercarial infection of wild Nile tilapia (Oreochromis niloticus) from Brazil

Fingerlings of Oreochromis niloticus collected in an artificial urban lake from Belo Horizonte, Minas Gerais, Brazil, were evaluated for natural infection with trematodes. Morphological taxonomic identification of four fluke species was performed in O. niloticus examined, and the total prevalence of metacercariae was 60.7% (37/61). Centrocestus formosanus, a heterophyid found in the gills, was the species with the highest prevalence and mean intensity of infection (31.1% and 3.42 (1–42), resp.), followed by the diplostomid Austrodiplostomum compactum (29.5% and 1.27 (1-2)) recovered from the eyes. Metacercariae of Drepanocephalus sp. and Ribeiroia sp., both found in the oral cavity of the fish, were verified at low prevalences (8.2% and 1.6%, resp.) and intensities of infection (only one metacercaria of each of these species per fish). These species of trematodes are reported for the first time in O. niloticus from South America. The potential of occurrence of these parasites in tilapia farming and the control strategies are briefly discussed.