Brackish Water Ecosystem Research Articles

Eight new Halophytophthora species from marine and brackish-water ecosystems in Portugal and an updated phylogeny for the genus.

During an oomycete survey in December 2015, 10 previously unknown Halophytophthora taxa were isolated from marine and brackish water of tidal ponds and channels in saltmarshes, lagoon ecosystems and river estuaries at seven sites along the Algarve coast in the South of Portugal. Phylogenetic analyses of LSU and ITS datasets, comprising all described Halophytophthora species, the 10 new Halophytophthora taxa and all relevant and distinctive sequences available from GenBank, provided an updated phylogeny of the genus Halophytophthora s.str. showing for the first time a structure of 10 clades designated as Clades 1-10. Nine of the 10 new Halophytophthora taxa resided in Clade 6 together with H. polymorphica and H. vesicula. Based on differences in morphology and temperature-growth relations and a multigene (LSU, ITS, Btub, hsp90, rpl10, tigA, cox1, nadh1, rps10) phylo-geny, eight new Halophytophthora taxa from Portugal are described here as H. brevisporangia, H.cele-ris, H.frigida, H. lateralis, H. lusitanica, H. macrosporangia, H. sinuata and H. thermoambigua. Three species, H.frigida, H.macrosporangia and H. sinuata, have a homothallic breeding system while the remaining five species are sterile. Pathogenicity and litter decomposition tests are underway to clarify their pathological and ecological role in the marine and brackish-water ecosystems. More oomycete surveys in yet undersurveyed regions of the world and population genetic or phylogenomic analyses of global populations are needed to clarify the origin of the new Halophytophthora species. Citation: Maia C, Horta Jung M, Carella G, et al. 2022. Eight new Halophytophthora species from marine and brackish-water ecosystems in Portugal and an updated phylogeny for the genus. Persoonia 48: 54 - 90. https://doi.org/10.3767/persoonia.2022.48.02..

Socioeconomic study of traditional fish farmers and trained farmers in the Indian Sundarbans ecosystem

AbstractThe Sundarbans, major marshy land, and brackish water ecosystem of the West Bengal were inhabited by many species of fishes which were the main dependants of the people living there. The present investigation was conducted using a questionnaire survey, participatory rural appraisal, key informant interviews, and focus group discussion and to assess the present state of production of major cultivable species of Sundarbans like mullet, shrimp, tilapia, mud-crabs, giant prawn and Asian seabass. A socioeconomic and technical survey of 45 trained and 45 traditional practitioners of aquaculture were conducted from May 2017 – April 2018. This study and appraisal intended to compare the socioeconomic relationship between traditional fish farmers and trained aquaculturists in Indian Sundarbans. The modern farmers usually practice the farming systems like Jayantirohu cultivation, white shrimp cultivation, genetically improved farmed tilapia, crabs fattening and crab culture; periphyton based giant prawn cultivation and Asian seabass culture with forage feeding with bait fishes. The trained farmers were enriched with much knowledge and information gained from various training, which the traditional farmers were lacking. It was found average benefit-cost ratio for traditional farming and modern farming system of 1:1.89 for traditional fish farmers and 1:3.13 for trained farmers. It was helping the modern practitioners to earn more profit to suffice their family needs as well as they were now accomplishing more safety, security measures for their family, investing more in their aquaculture practices. The yield of fish culture was affected by pond conditions, family labor engagement, and resource endowment of the fisher family. Linkage with formal financial institutions, subsidized input support from the fishery department, and investment in human resource development of farmers might be some point of intervention to boost fish culture in the coastal zone of West Bengal, India.

Eight new Halophytophthora species from marine and brackish-water ecosystems in Portugal and an updated phylogeny for the genus

During an oomycete survey in December 2015, 10 previously unknown Halophytophthora taxa were isolated from marine and brackish water of tidal ponds and channels in saltmarshes, lagoon ecosystems and river estuaries at seven sites along the Algarve coast in the South of Portugal. Phylogenetic analyses of LSU and ITS datasets, comprising all described Halophytophthora species, the 10 new Halophytophthora taxa and all relevant and distinctive sequences available from GenBank, provided an updated phylogeny of the genus Halophytophthora s. str. showing for the first time a structure of 10 clades designated as Clades 1–10. Nine of the 10 new Halophytophthora taxa resided in Clade 6 together with H. polymorphica and H. vesicula. Based on differences in morphology and temperature-growth relations and a multigene (LSU, ITS, Btub, hsp90, rpl10, tigA, cox1, nadh1, rps10) phylogeny, eight new Halophytophthora taxa from Portugal are described here as H. brevisporangia, H. celeris, H. frigida, H. lateralis, H. lusitanica, H. macrosporangia, H. sinuata and H. thermoambigua. Three species, H. frigida, H. macrosporangia and H. sinuata, have a homothallic breeding system while the remaining five species are sterile. Pathogenicity and litter decomposition tests are underway to clarify their pathological and ecological role in the marine and brackish-water ecosystems. More oomycete surveys in yet undersurveyed regions of the world and population genetic or phylogenomic analyses of global populations are needed to clarify the origin of the new Halophytophthora species.

Increases of opportunistic species in response to ecosystem change: the case of the Baltic Sea three-spined stickleback

Abstract Under rapid environmental change, opportunistic species may exhibit dramatic increases in response to the altered conditions, and can in turn have large impacts on the ecosystem. One such species is the three-spined stickleback (Gasterosteus aculeatus), which has shown substantial increases in several aquatic systems in recent decades. Here, we review the population development of the stickleback in the Baltic Sea, a large brackish water ecosystem subject to rapid environmental change. Current evidence points to predatory release being the central driver of the population increases observed in some areas, while both eutrophication and climate change have likely contributed to creating more favourable conditions for the stickleback. The increasing stickleback densities have had profound effects on coastal ecosystem function by impairing the recruitment of piscivorous fish and enhancing the effects of eutrophication through promoting the production of filamentous algae. The increase poses a challenge for both environmental management and fisheries, where a substantial interest from the pelagic fisheries fleet in exploiting the species calls for urgent attention. While significant knowledge gaps remain, we suggest that the case of the Baltic Sea stickleback increase provides generalisable lessons of value for understanding and managing other coastal ecosystems under rapid change.

Onset of Late Cretaceous diversification in Europe\u2019s freshwater gastropod fauna links to global climatic and biotic events

The Mesozoic rise of the European freshwater gastropod fauna is still poorly understood. Compared to the well documented Cenozoic history, little is known about the patterns and processes underlying the early diversification preceding their extinction crisis at the K–Pg boundary. We assess what is probably a first pulse of diversification of the Cenozoic-type fauna in the Late Cretaceous along with the potential abiotic and biotic controls for shifts in species diversification. We find strong support that the increase in the speciation rate in the Santonian (~ 85 Myr ago) is linked to a global sea level rise, which caused extensive flooding of continental areas and the formation of vast brackish-water ecosystems. The following decline of the speciation rate coincides with a rise in diversity and reflects increasing interspecific competition. The peak in the speciation rate postdates the Cenomanian–Turonian Thermal Maximum, which probably limited the potential for diversification among freshwater gastropods due to ecological constraints. The peak coincides moreover with the end phase of the Cretaceous Terrestrial Revolution, which sparked the radiation of angiosperms. The expansion and diversification of flowering plants, being an important food source for freshwater gastropods today, could have formed a necessary basis for gastropod diversification.

Trophic Relationships and Structure of Brackish Water and Coastal Ecosystems: Possible Common 56 Trends between African and Asian Waterbodies

In the present synthesis, trophic relationships of eight coastal and brackish ecosystems in some countries of Africa and Asia were reviewed (Ivory Coast, Benin, Senegal, in Africa, Sri Lanka, Vietnam, Thailand and China in Asia). For these highly productive and complex ecosystems, knowledge on the biological and ecological functioning of fish faunas utilizing, as well as, the environmental forces contributing to geographic specificities of these environments is vital for their sustainable management and conservation. Recognizing that anthropogenic activities impact not only the environment but the dynamics and functioning of its living resources, untangling ecosystem processes can increase understanding of its current health and resilience to change. Effective management of these ecosystems should focus on a framework based on a sound understanding of ecosystem

First record of pouched octopus, Cistopus platinoidus in a tropical estuary

Octopuses are marine benthic stenohaline organisms that exhibit a short range of migration within marine habitats and avoid brackish or freshwater environments. The present document is the first record of 'pouched octopus', Cistopus platinoidus Sreeja et al. 2015, from a tropical estuarine system. We collected 15 specimens of C. platinoidus from the set bag nets operated in Narmada estuary, located 40 km away from the river mouth with an in-situ salinity of 17.63. This report is a new finding of an octopus species from a brackish water ecosystem outside its normal inhabitance range to the best of our knowledge.

Benthic Diatoms on Sheltered Coastal Soft Bottoms (Baltic Sea)—Seasonal Community Production and Respiration

Benthic diatom communities dominate sheltered shallow inner coastal waters of the atidal Southern Baltic Sea. However, their photosynthetic oxygen production and respiratory oxygen consumption is rarely evaluated. In the Baltic Sea carbon budget benthic diatom communities are often not included, since phytoplankton is regarded as the main primary producer. Therefore, two wind-protected stations (2–49-cm depths) were investigated between July 2010 and April 2012 using undisturbed sediment cores in combination with planar oxygen optodes. We expected strong fluctuations in the biological activity parameters in the incubated cores over the course of the seasons. The sediment particles at both stations were dominated by fine sand with a median grain size of 131–138 µm exhibiting an angular shape with many edges, which were less mobile compared to exposed coastal sites of the Southern Baltic Sea. These sand grains inhabited dense communities of rather small epipsammic diatoms (<10 µm). Chlorophyll a as a biomass parameter for benthic diatoms fluctuated from 64.8 to 277.3-mg Chl. a m−2 sediment surface. The net primary production and respiration rates exhibited strong variations across the different months at both stations, ranging from 12.9 to 56.9 mg O2 m−2 h−1 and from −6.4 to −137.6 mg O2 m−2 h−1, respectively. From these data, a gross primary production of 13.4 to 59.5 mg C m−2 h−1 was calculated. The results presented confirmed strong seasonal changes (four-fold amplitude) for the activity parameters and, hence, provided important production biological information for sheltered sediments of the Southern Baltic Sea. These data clearly indicate that benthic diatoms, although often ignored until now, represent a key component in the primary production of these coastal habitats when compared to similar studies at other locations of the Baltic Sea and, hence, should be considered in any carbon budget model of this brackish water ecosystem.

Next-Generation Smart Response Web (NG-SRW): An Operational Spatial Decision Support System for Maritime Oil Spill Emergency Response in the Gulf of Finland (Baltic Sea)

The Baltic Sea is a unique and sensitive brackish-water ecosystem vulnerable to damage from shipping activities. Despite high levels of maritime safety in the area, there is a continued risk of oil spills and associated harmful environmental impacts. Achieving common situational awareness between oil spill response decision makers and other actors, such as merchant vessel and Vessel Traffic Service center operators, is an important step to minimizing detrimental effects. This paper presents the Next-Generation Smart Response Web (NG-SRW), a web-based application to aid decision making concerning oil spill response. This tool aims to provide, dynamically and interactively, relevant information on oil spills. By integrating the analysis and visualization of dynamic spill features with the sensitivity of environmental elements and value of human uses, the benefits of potential response actions can be compared, helping to develop an appropriate response strategy. The oil spill process simulation enables the response authorities to judge better the complexity and dynamic behavior of the systems and processes behind the potential environmental impact assessment and thereby better control the oil combat action.

Co-occurrence and potential resource partitioning between oligochaetes and chironomid larvae in a sediment depth gradient

Although detritivorous Tubificinae and chironomid larvae are important groups in functioning of both, fresh and brackish water ecosystem, their co-occurrence patterns in sediment is weakly known. We carried out two-year-long research in the brackish Vistula Lagoon (southern Baltic Sea), where both Tubificinae (Limnodrilus hoffmeisteri and Potamothrix hammoniensis) and larvae of Chironomus balatonicus occur in high densities. Because of different source of their food, we hypothesized that the ecological interactions between those two groups of detritivores are not antagonistic, thus allowing for their co-occurrence along the depth of sediment profile with lack of competition for space. Here we show that maximum burrowing depth, occasionally reaching 25 cm was significantly affected by the total density of the each group in the entire core. Tubificinae and C. balatonicus showed the highest density at 0–10 cm depth, where they co-occurred most frequently, with significant co-occurrence in the layers of 0–2 cm and 2–5 cm. We propose a hypothetical model of interactions between apparently the same functional groups and the complementary role they play in sediment reworking. It points to their coexistence in the shared microhabitat, but using space and food resources differently. Also, the consequences of their activity and habitat structuring are opposite—Chironomus larvae mostly affect the deeper layers of the sediments, while Oligochaeta both the deeper and surface layers. Thus, their requirements and ecological roles seem not to overlap, preventing competitive exclusion and allowing for co-occurrence.

Phosphorus sorption behaviour of the largest brackish water lagoon, South Asia

The Chilika Lagoon is the largest brackish water ecosystem in the Asian continent and is a Ramsar site. Here, the sorption–desorption study was standardized simulating the environmental condition of the Chilika, to ascertain whether phosphorus (P) is the source or sink for sediments of the coastal ecosystem. The sorption behaviour of sediment phosphorus was better fitting into the modified Langmuir model. The effects of salinity, pH, and temperature on phosphorus sorption were found to be better understood by nonlinear relationships. The sorption was recorded to increase at its lower concentrations with increasing of mentioned parameters, when it decreased beyond some threshold values. The maximum phosphorus sorption capacity (Qmax) was more (258 mg/kg) in the freshwater stretch of the lagoon; Northern Sector compared to the relatively saline stretches, i.e., Outer Channel (219 mg/kg) and Southern Sector (237 mg/kg) (p < 0.05). This study will help to control eutrophication by increasing P sorption.

A novel myxozoan parasite, Ellipsomyxa boleophthalmi sp. nov. (Myxozoa: Ceratomyxidae) in the brackishwater fish, Boleophthalmus dussumieri Valenciennes, 1837 (Perciformes: Gobiidae) from India.

A novel myxozoan parasite is identified and described from mudskipper, Boleophthalmus dussumieri, collected from a brackishwater ecosystem in Maharashtra, India. Ellipsomyxa boleophthalmi sp. nov. was found in the gallbladder of 58 of 60 fish examined (96.7%). The parasite formed disporous plasmodia that varied in size and shape, and the thin-walled, ellipsoidal and elongated myxospores measured 9.0-10.7 × 6.0-7.8 μm. The two, spherical polar capsules measured 2.7 μm in diameter and enclosed 3-4 coils of polar tubules. Histological observations of infected gallbladder revealed the attachment of disporous plasmodial stages of the parasite to the gallbladder wall with fine pseudopodia. Under the scanning electron microscope (SEM), the myxospores showed a distinct central sutural line and two distinct depressions on the opposite sides at the openings of polar capsules. SEM also revealed the engulfment of microvilli of gallbladder wall by pseudopodia of the plasmodial stages. Analysis of the partial fragment of the SSU rDNA region (1386 bp) showed less than 98% sequence similarity with the other reported Ellipsomyxa spp. In the phylogenetic tree, the present species formed as a distinct subclade within the major clade of Ellipsomyxa spp. The unique morphological and morphometric features of the myxospore, together with the molecular analysis, allowed us to conclude that the present myxozoan is a new species and is named Ellipsomyxa boleophthalmi sp. nov., after the generic name of the host. This is the first report on the occurrence of the genus Ellipsomyxa in B. dussumieri.

Genetic population structure of a top predatory fish (northern pike, Esox lucius) covaries with anthropogenic alteration of freshwater ecosystems

Abstract Esox lucius L. (northern pike) inhabits river, lake, and brackish water ecosystems of the temperate region in North America and Eurasia. In many areas of its native range, the species is confronted with human‐induced disturbances that can affect local and regional genetic diversity. Conservation of genetic diversity constitutes an important policy objective. Therefore, we investigated how the genetic population structure and patterns suggestive of hybridisation among subpopulations from different catchments vary with the type of ecosystem (river vs. lake) and the integrity of the ecosystem assessed using ecological status assessments of the European Water Framework Directive and indices of the wetland quality (in rivers) and trophic state (in lakes). In total, 1,384 pike samples from the North, Baltic, and Black Sea drainages in Germany were analysed. We differentiated between metapopulations from each hydrogeographic region using genotypes from 15 microsatellites and mitochondrial cyt b sequences. Individual populations showed signs of genetic admixture ranging from almost zero to complete replacement by foreign genotypes originating from different catchments. Hierarchical general linear modelling revealed a significantly positive association of the degree of genetic hybridisation with decreasing ecological status. An eroded population substructure indicative of hybridisation was also significantly elevated in rivers relative to lakes and in heavily modified water bodies. Results were consistent when using ecological status assessments by the Water Framework Directive and an alternative environmental quality index based on the health of wetlands in rivers and trophic state in lakes. We speculate that macrophyte loss through loss of wetlands or in response to eutrophication fostered genetic mixing among different subpopulations, which were brought into secondary contact either due to stocking or due to natural dispersal from foreign catchments. Our findings suggest that anthropogenic alteration of freshwater ecosystems may influence the genetic structures present in a freshwater top piscivore at both local and regional scales.

Ecology of breeding habitats of mosquito population and screening for virus of Japanese encephalitis and West Nile in the coastal area of Kerala, India.

Japanese encephalitis (JE) and West Nile virus (WNV) are two mosquito-borne diseases of medical and veterinary importance. Climate impacts in certain ecosystems are better understood; however, coastal brackish water ecosystems and their role in vector borne viral diseases have not been well studied. Hence, the aim of this study is to evaluate the distribution, spatial pattern as well as the screening of these mosquitoes for JE and WN virus in coastal area of Alappuzha district, Kerala, India. Immature mosquitoes were collected using dipper methods along the coastal wetlands areas. Adult mosquitoes were collected in four sampling sites with light trap filled with dry ice, operating overnight. The collected mosquitoes were identified by species, using the taxonomic keys. Mosquitoes were pooled for virus detection. Water samples were collected using standard methods. The total quantity of rainfall and salinity varied from zero to 365.2 mm and from 1.5 to 28 ppt respectively. A total of 10,695 adult mosquitoes and 38,083 immatures revealed the presence of five genus and 23 species. The most predominant species was Culex tritaeniorhynchus. Immature collections Cx. sitiens was the only one species collected during the summer season and in the monsoon season the pond was replaced by fresh water mosquitoes such as Cx. tritaeniorhynchus and Cx. gelidus. A total of 186 pools were screened for JEV and WNV. However, none of the pools were found as positive for the virus. The major vector of JEV Cx. tritaeniorhynchus and Cx. gelidus have adapted to immature development in coastal brackish water habitats. The public health authorities need to recognize thepotential impact on human health of brackish water-adapted mosquito vectors that weretraditionally considered to be freshwater species, and take appropriate surveillance and control measures.

ENVIRONMENTAL VULNERABILITY ASSESSMENT IN THE SOUTH-WEST COASTAL REGION OF BANGLADESH USING PRINCIPAL COMPONENT ANALYSIS

Being located in a low-lying coastal zone and having a unique brackish water ecosystem, the South-west region of Bangladesh is highly susceptible to environmental vulnerability. An assessment of environmental vulnerability over this large area of 24,188 km2 is a complex process and one of the most essential parts for any coastal zone management. Since the changes in the environmental indicators are posing adverse impacts, the environment tends to be more vulnerable. This study assesses the environmental vulnerability in 40 Upazilas (lower level of the administrative unit) in the South-west region of Bangladesh. After reviewing the literature, this study incorporated 10 relevant indicators (i.e. soil type, average temperature, vegetation change, population density, population change, road density, surface salinity, Cumulative Dry Day (CDD), Cumulative Wet Day (CWD), groundwater level). Principal Component Analysis (PCA) was applied to find the weight for each indicator in IBM SPSS 20 software and the values were normalized into a unified dimension. The generated environmental vulnerability map is assorted into five vulnerability groups consisting of very low, low, medium, high, very high vulnerabilities with an interval of 0-0.05, 0.05-0.4, 0.4-0.5, 0.5-0.6, 0.6-1.0 respectively. From the spatial analysis, it has been seen that the vulnerability groups representing very low, low, medium, high, and very high contain 10percent, 35percent, 28percent, 17percent, and 10percent of the Upazilas, respectively. The findings of environmental vulnerability assessment can support effective guidance for long-term environmental management in terms of coastal zone management. The development framework can be assessed at different spatial and temporal scales in the coastal zone with the availability of environmental indicator data and by applying the PCA method.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/iQ_CwlOBCJE

An Annotated Checklist to the Commonly Harvested Crabs (Crustacea: Decapoda) from Marine and Brackish Water Ecosystems of Palawan, Philippines

An Annotated Checklist to the Commonly Harvested Crabs (Crustacea: Decapoda) from Marine and Brackish Water Ecosystems of Palawan, Philippines

The Plankton Composition from the Lagoon to the Marine Entrance at the West Part of Segara Anakan Mangrove Ecosystem in Cilacap

There was a unique brackish water ecosystem and affected a chance in the plankton composition at lagoon and riverside in Segara Anakan Cilacap. This study aimed to map phytoplankton and zooplankton composition consisting of freshwater and marine plankton from the lagoon to the marine entrance in the west part of Segara Anakan Cilacap. The survey method was taken with purposive random sampling in fourteen stations and four replicates with new and full moon conditions from March to April 2018 in a wet season. The result showed 52 species of plankton. All species belonged to phylum Cyanophyta (9 species), Chlorophyta (13 species), Chrysophyta (19 species), Euglenozoa (2 species), Rotifera (2 species) and Arthropoda (7 species). Of the 52 species collected in all stations and replicates, phytoplankton has a greater species richness (41 species) than zooplankton (11 species). And also, freshwater plankton (47 species) has a higher species richness than marine plankton (5 species) due to the wet season condition causing freshwater enters brackish water. The largest freshwater of River Citanduy enters the brackish water of Segara Anakan mangrove ecosystem in Cilacap and causing the freshwater phytoplankton abundance, especially Staurastrum sp. in inland waters of Segara Anakan Cilacap.

Checklist of the fresh and brackish water snails (Mollusca, Gastropoda) of Bénin and adjacent West African ecoregions

Currently no comprehensive checklist of fresh and brackish water gastropods from Bénin exists, and those for adjacent West African areas are outdated. Yet, such checklists provide essential biodiversity information and a consistent taxonomic and nomenclatural framework for that biodiversity. Here a first checklist of the fresh and brackish water gastropods from Bénin and adjacent West African ecoregions is presented, based on an extensive literature review and field surveys between September 2014 and June 2019 in six major fresh and brackish water ecosystems in Bénin. This inventory includes information on synonymy, species distribution in West Africa, habitats, and conservation status. The fresh and brackish water gastropod fauna includes 60 species, belonging to 28 genera and 16 families. Pachychilidae, Ampullariidae, Neritidae, and Bulinidae were the most diverse families with 9, 8, 7, and 7 species, respectively. However, literature and field data indicated that 23 species observed in West African basins that extend to Bénin do not occur in the territory of Bénin. These species were not detected in our field surveys, most likely because they are rare at collecting sites. Of the 60 species included, five are classified as “Data Deficient”, 43 as “Least Concern”, two as “Nearly Threatened”, one as “Vulnerable”, and six as “Endangered” by the IUCN, whereas the remaining three species were not evaluated. Because the taxonomy of fresh and brackish water gastropods in West Africa is still largely based on morphology, comparative molecular and taxonomic studies may result in substantial revisions of this checklist over the coming years.

Fish diversity in freshwater and brackish water ecosystems of Russia and adjacent waters

Fish diversity in freshwater and brackish water ecosystems of Russia and adjacent waters

Salinity Influence on Copper Sulphate and Lead Nitrate Combined Toxicity Against &lt;i&gt;Oreochromis niloticus&lt;/i&gt;

Brackish water ecosystems characterized by fluctuating physicochemical parameters are more susceptible to the toxic effects of heavy metals acting singly or jointly. This study investigated the effect of salinity variations on the joint action toxicity of copper sulphate (CuSO4) and lead nitrate Pb(NO3)2 against fingerlings of Oreochromis niloticus. Fingerlings were exposed to binary mixtures of CuSO4 and Pb(NO3)2 (ratios 1:1 and 1:4) at varying salinities (0‰, 2‰, 12‰ and 18‰) in laboratory bioassays. The binary mixtures of the heavy metals were least toxic to the fish at 12‰ with 96 h LC50 values of 115.558 mg l-1 and 198.274 mg l-1 compared to 8.465 mg l-1 and 16.884 mg l-1 for 0‰, 46.084 mg l-1 and 69.843 mg l-1 for 2‰ and 13.196mg l-1 and 100.567 mg l-1 for 18‰ at ratios 1:1 and 1:4 respectively. Analysis using the Synergistic Ratio Model (SR) showed that both heavy metals were less toxic to the fish species when acting jointly irrespective of ratio than when acting singly at 12‰. Therefore, the need to consider the fluctuating salinity and joint interaction of heavy metals in setting ecologically safe limits for the discharge of effluents containing heavy metals into the aquatic ecosystems is important.&#x0D; Key words: Salinity, Heavy Metals, Toxicity, Oreochromis niloticus