Cochin Estuary Research Articles

Large scale screening and quantification of micropollutants in fish from the coastal waters of Cochin, India: Analytical method development and health risk assessment

Urban estuarine and coastal water receive several micropollutants through industrial and agricultural influxes. The bioaccumulation of these micropollutants in fish and their entry into the coastal population's food chain raises significant food safety concerns. Hence, a comprehensive analytical method was developed for ultra-trace level quantification of 345 micropollutants in fish. The optimized sample preparation method could extract compounds suitable for both GC–MS/MS and LC-MS/MS analysis simultaneously. The target list of contaminants included 278 agricultural pesticides and also 102 endocrine disruptors covering polyaromatic hydrocarbons, polychlorinated biphenyls, organochlorines, and endocrine-disrupting pesticides. The GC–MS/MS with large volume injection (LVI) technique, and LC-MS/MS operating in MRM mode, achieved an LOQ of <2.00 ng/g for most of the analytes. The extraction strategy involved tri-phase partitioning between water, acidified acetonitrile, and hexane, followed by salting out. Dispersive solid phase cleanup (dSPE) with C18, Z-Sep+, CaCl2, and MgSO4 was able to reduce the matrix influence, and the method achieved satisfactory recovery in the range of 70.0–120.0 % for all the target analytes. The repeatability and reproducibility relative standard deviation values of the measured analytes were <20.0 %, and the Horwitz ratio values were well below 2. The method was used to accurately measure the target micropollutants in fish from the Cochin estuary, the highly urbanized portion of the Vembanad Lake, and an important Ramsar site. At least one or more of the 41 different micropollutants were identified and quantified in about 90.7 % of the 108 samples analyzed. The importance of large-scale screening and trace-level quantification methods in environmental monitoring and risk assessment is underscored by the results. The risk assessment showed a moderate risk of exposure to the nearby coastal population through the food chain.

Influence of cadmium and zinc contamination on the sediment microbiome of estuarine and coastal ecosystems in the Southwest Coast of India.

Metals and their nanoparticles can induce toxicities that influence the survival of both microorganisms and macroorganisms. The current study reports on the impact of heavy metal pollution on the microbiome of estuarine and coastal sediments, where the settling and final remineralization of organic matter occur. Sediment samples collected from the Cochin estuary along the southwest coast of India and its adjacent coast showed high concentrations of cadmium (Cd) and zinc (Zn). The contamination factor (CF), calculated by comparing the concentration of metals in each station with that of shale value for Cd and Zn, ranged from 5.2 to 8.7 and 1.5 to 2.0 respectively, in the estuarine and coastal stations. Microbiome analysis revealed that bacteria were common across all stations but varied in relative abundance. Proteobacteria, Chloroflexi, Actinobacteria, Desulfobacteria, and Acidobacteria were the major bacterial phylum found in all stations. More than 70% of the bacteria were tolerant to 1mM concentration of Cd. The findings of our study suggest that metal pollution can influence the microbiome of sediments in the estuaries and coasts. Bacteria with metal tolerance may dominate in polluted areas, but their participation in remineralization may be impaired, as evident in our previous reports. This impairment could ultimately influence the dynamics of the food web and the biogeochemical cycling of nutrients, necessitating further research.

Sediment microbial diversity, functional potentials, and antibiotic resistance pattern: a case study of Cochin Estuary core sediment.

Marine sediments are an important part of the marine environment and the world's greatest organic carbon source. Sediment microorganisms are important regulators of major geochemical and eco-environmental processes in marine environments, especially nutrient dynamics and biogeochemical cycles. Despite their importance, core marine microorganisms are virtually unknown due to a lack of consensus on how to identify them. Most core microbiotas have been characterized thus far based on species abundance and occurrence. The combined effects of habitat and depth on benthic bacterial communities and ecological functions were studied using "Next-Generation sequencing (NGS) and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) predictive functional profiling" at the surface (0.2cm) and bottom depth (250cm) in a sediment core sample from Cochin Estuary, Kerala, India. The results showed that bacterial diversity and richness were significantly higher in the surface sediment sample with the most abundant phyla being Proteobacteria, Acidobacteria, Chloroflexi, and Bacteroidetes. The major metabolic functions were metabolism, followed by environmental information processing and genetic information processing. Antibiotic resistance genes between the surface and bottom samples help to understand the resistance pattern among multidrug resistance is the most prominent one. Among viruses, Siphoviridae is the dominant family, followed by Myoviridae. In the case of Archea, Crenarchaeota is dominant, whereas among eukaryotes phyla Streptophyta and Chordata were dominant in the surface and the bottom samples respectively.

Ovarian Development by Visual and Histological Investigation of &lt;i&gt;Arius subrostratus&lt;/i&gt; (Shovelnose Sea Catfish) from Cochin Estuary, India

Ovarian Development by Visual and Histological Investigation of &lt;i&gt;Arius subrostratus&lt;/i&gt; (Shovelnose Sea Catfish) from Cochin Estuary, India

Metal partitioning in sediments and risk assessment of a ramsar site-Cochin estuary, South West India

Geochemical partitioning of sediment bound metals in Cochin estuary were determined by sequential extraction to unravel the processes controlling their distribution, mobility and contamination status. Most of the metals recorded higher content at residual and exchangeable fractions. Abundance of Cd, Zn and Mn in bioavailable form (promoted by surface adsorption on fine grained sediments) was sourced to industrial operations, municipal sewage and agriculture effluents. Pyrite formation effectively controls the fraction distribution of redox sensitive elements- Mn and Fe. Scavenging by Fe-Mn oxide was dominant process regulating the accretion of metals -Zn, Ni, Cr, Co, Cd, Mn whereas organic matter complexation facilitate the accumulation of the metals-Mn, Co, Cu and Zn. Contamination due to Zn and Cd was substantiated by enrichment factor (range for Zn: 4.42–57.22; range for Cd: 0.02–0.37), contamination factor (range for Zn: 0.51–22.19; range for Cd: 3.30–60.67 and geoaccumulation index (range for Zn: 0.10–4.45; range for Cd: 0.66–12.18). Elevated PLI (Range: 0.19–1.58) indicated metal inputs from anthropogenic activities. Potential ecological risk values >40 implied that Cd, Zn and Pb can induce risk to the ecosystem.

Enrichment and Bioavailability of Phosphate in a Highly Urbanized Zone of Cochin Estuary, South India

ABSTRACT Sequential extraction (SEDEX method) was employed to explore the distribution of sediment-bound phosphorus (P) fractions and the bioavailability of P in Cochin estuary. Concentration of P fractions in surface sediments of the study area ranged as follows: Detrital P > Organic P > Authigenic P > Exchangeable P > Iron-bound P. Generally increasing trend was displayed by all the phosphate fractions toward the downstream sites due to effluent discharges from industrial, domestic, municipal, agricultural sectors and destruction of mangrove forests. The elevated levels of inorganic phosphorus (133.55–918.73 mg/kg) reflected the large-scale delivery of sediment loads associated with great floods during 2018 & 2019. Significant correlations of fine-grained sediment particles with all phosphate fractions indicated surface adsorption as a dominant distribution mechanism. Concentration of iron-bound phosphorus was controlled by adsorption on iron oxy-hydroxides. The buildup of bioavailable phosphate (range: 23.76 to 49.97%) indicate the fact that the estuarine sediments function as a sink for the nutrient. The upper and middle part of the study area recorded more severe contamination and eutrophication risk as indicated by phosphorous pollution index (range: 0.31 to 2.56).

Assessment of the age and growth of three fin fish species from a tropical estuary (Cochin, west coast of India)

Data on three fin fish species were collected from the Cochin estuary (part of the Vembanad–Kol wetland system, India) from January 2018 to December 2019. The present study presents the first comprehensive results on fisheries demographics within this estuary, based on length-frequency data, to calculate vital demographic dynamic factors and estimate the stock of the commercially important three fin fish species. A variety of evaluations were conducted using the FiSAT II program. Caranx heberi had an asymptotic length (L) of 304.5 mm and a growth constant (K) of 1.1 year-1, while Etroplus suratensis had an asymptotic length (L) of 158.55 mm as well as a growth constant (K) of 1.1 year-1. For all the species studied, the age at zero-length (t0) had been calculated and varied from −0.04 to −0.14. Oreochromis mossambicus had longevity (tmax) of 4.76 yr and a growth performance index (ɸ) of 4.51, whereas E. suratensis had 2.72 and 4.44. E. suratensis had overall mortality (Z), natural mortality (M), and fishing mortality (F) of 2.93, 1.2 and 1.73 year-1, respectively, while C. heberi had 1.42, 1, and 0.42 year-1. The present exploitation level is greater than the optimum exploitation rate, according to the relative yield per recruit (Y/R) study, indicating over-exploitation of two examined finfish species and moderate exploitation for one species. Management measures such as mesh size limitations, restricted fishing efforts, and the proclamation of restricted seasons are required to save these species from extinction.

Indigenous craft and gears used for crab fishery in Cochin estuary, Kerala, southwest coast of India

This paper presents an overview of fishing gears and crafts operated for crab fishery in the Cochin estuary. A survey was made in selected areas of the Cochin estuary to study the design and operational details of indigenous craft and gears used in crab fishing. Primary data on crab fishery were collected from fish landing centers and fishing villages through a structured questionnaire. Crab gillnets and ring nets are the dominant artisanal gear supporting crab fishery throughout the study area. Long lines were one of the widely deployed fishing gears for the crab fishery, which is now operational only in limited areas of the Cochin estuary. Incidental catch of crabs is also noted in the stake net and Chinese dip net. The wounding gears and traditional fishing techniques, viz., vazhuka method and midrib trap, are not deployed in commercial crab fishery as they result in low-value realization. The survey discloses that ring net and crab gillnet accounted for 98% of the crab landing along the Cochin estuary. Scylla serrata and Scylla olivacea are the essential species contributing to inland crab fishery along the study area. Wooden canoes belonging to 3 to 7 m in length overall (LOA) are employed for crab fishing. Migrant fishermen use Coracles and the FRP canoes for crab gill net operations along the stretches of the backwaters.

Spatiotemporal variation of microbial communities in surficial sediments of Cochin estuary, southwest coast of India.

Microorganisms play a major role in the degradation of organic matter in sediments. However, the spatiotemporal variation and factors affecting these communities are not clearly understood. At the same time, conventional hydrographic and geochemical parameters do not offer an accurate assessment of transitional ecosystems. PLFA biomarkers which are specific to different taxonomic groups of microorganisms are able to provide a detailed assessment of the community composition in an environment and reflect a more direct assessment of the biological health of transitional ecosystems. We, therefore, conducted a comparison of PLFA biomarkers at four stations (Barmouth, B; Vaduthala, V; Munambam, M; and Arookutty, A) during three seasons (pre-monsoon, PRE; monsoon, MON; and post-monsoon, POST) in the Cochin estuary (CE). Each of the stations represented either a reference point (B), high pollution (V), high salinity (M), or low pollution (A). The communities determined using PLFA profiles could be categorized into six major groups with each group capable of reflecting the state of the ecosystem which correlated with the conventional parameters. The six groups were: G + ve Bacillota (formerly Firmicutes) and G-ve anaerobes (G-I), G-ve aerobic prokaryotes (G-II), ectomycorrhizal fungi (G-III), arbuscular mycorrhizae (G-IV), type-I methanotrophs (G-V), and microeukaryotes (G-VI). The prokaryotes were predominant in sediments amounting to over 78% of the total PLFAs detected, followed by the microeukaryotes. The freshwater-influenced stations were partially anaerobic in nature during PRE and MON and were mainly affected by both marine and terrestrial organic matter inputs, at times prominent in sewage matter. During POST season, CE behaves uniformly, especially in station M. Salinity and DO of BW and texture and organic matter of the sediment were the driving forces for microbial community structure. The reduced presence of cyclopropane fatty acids suggested that the CE was not under any stress during the study period. Our results using PLFA-based community profiling not only provide the fundamental information required to quickly access the impact of stress and other environmental inputs on the CE but also offer a more robust and realistic assessment of the nature of microbial communities in the ecosystem. A periodic and systemic assessment of PLFA profiles at these stations in CE throughout the year will enable the generation of enough metadata enabling a better understanding of this ecosystem and its efficient management in the long term.

Variations in biomarkers at different biological levels in the wild fish species Arius subrostratus (Vallenciennes, 1840) from a polyaromatic hydrocarbon (PAH) contaminated estuary in India

The present study investigated the variations in biomarkers of polyaromatic hydrocarbons (PAH) in wild fish Arius subrostratus from the Cochin estuary. Growth indices, hematological parameters, antioxidants, histopathology, and apoptosis-related gene expressions were analyzed and compared to the PAH quantified from bile. Biliary PAH in fishes from the middle estuarine area was the highest followed by the lower and upper estuarine areas (sampling sites grouped based on their position, hydrodynamics, and possible source of PAH). As the biliary PAH increased, the condition factor decreased, whereas the hepato-somatic index increased. Hematology showed signs of macrocytic anemia with decreased RBC and hematocrit. However, antioxidant enzymes were found to be an unsuitable biomarker of PAH exposure in wild fishes. The major histological observations in the liver were hepatocellular nuclear polymorphism, fibrosis, and vacuolization. The expression of GST, Bax, Cytochrome C, CYP1A1, and p53 were upregulated in fishes from the most contaminated sites. The significant alterations in the growth indices, hematology, histopathology, and apoptosis-related gene expression of A. subrostratus with the change in biliary PAH suggest that it can be used as a species for monitoring PAH. The study further observed the complexities of using biomarkers for monitoring PAH contamination and impact assessment in estuaries.

Inter-seasonal variation in nitrogen uptake rates of the eutrophic Cochin estuary and adjacent coastal Arabian Sea

The study assessed the Cochin estuary and adjacent coastal Arabian Sea for their seasonal variation in nitrate (NO3−) and ammonium (NH4+) uptake rates by total and nano + picoplankton using the 15N tracer technique. The results suggested that the NO3− and NH4+ uptake rates in the Cochin estuary are higher than those in the adjacent coastal Arabian Sea. NO3− and NH4+ uptake rates in the nearshore stations in the off Cochin station were high, indicating the influence of the eutrophic estuary. NO3− and NH4+ uptake rates conducted in off Mangalore transect were significantly lower than those of the off Cochin as it does not have an exchange with eutrophic systems. The nano + picoplankton's contribution to the total DIN uptake rates in the Cochin estuary was 77–98 %, indicating the relevance of nano + pico phytoplankton in the N cycling of the region.

Age and growth study of two fin fish species from a tropical estuary

Data on two fin fish species were collected from the Cochin estuary (part of the Vembanad–Kol wetland system) from January 2018 to December 2019. The present study presents the first findings on fisheries demographics in these estuaries, based on length–frequency​ data, to calculate vital demographic dynamic factors and estimate the stock of these commercially important fish species. A variety of evaluations was conducted using the FiSAT II program. Pseudetroplus maculatus had an asymptotic length (L) of 97.6 mm as well as a growth constant (K) of 1.2 year-1. For all the species studied, the age at zero-length (t0) had been calculated and varied from −0.095 to −0.2. Gerres setifer had longevity (tmax) of 5.66 years and a growth performance index (ϕ) of 4.03, whereas P. maculatus had 2.5 and 4.06. P. maculatus had overall mortality (Z), natural mortality (M), and fishing mortality (F) of 3.04, 1.45, and 1.58 year1, respectively, while G. setifer had 1.14, 0.77, and 0.37 year1. The present exploitation level is greater than the optimum exploitation rate, according to the relative yield per recruit (Y/R) study, indicating over-exploitation of three examined finfish species and moderate exploitation for two species. Management measures such as mesh size limitations, restricted fishing efforts, and the proclamation of restricted seasons are required to save these species from extinction.

Occurrence and risk assessment of total mercury, methylmercury and other selected trace metals in the surface sediments of the Cochin Estuary, Southwest Coast of India

This study assesses the ecological risk and impact of anthropogenic activities in the Cochin estuary – a Ramsar site – by trace metal indices in surface sediment collected from thirteen sampling stations in three seasons. The trace metals analyzed are THg, MeHg, Pb, Cu, Cd, Zn, Ni, Co, Mn, Cr, Fe, and Al in the surface sediments and their spatio-temporal variation is recorded. Pollution indices (i.e., Enrichment factor, Index of geoaccumulation, sediment quality guidelines, pollution load index, and potential ecological risk index) were applied to ascertain the sediment quality. The distribution pattern of Cr, Zn, and Cd revealed higher concentrations in the northern arm of the estuary and near the industrial regions indicating non-geogenic inputs. The concentration of THg and MeHg exhibited spatial and temporal variations and were higher than the background values. The results showed that higher levels of trace metals were found in the northern part of the Cochin Estuary, which could be attributed to the weak flow and significant input of industrial effluents.

Trace Metal Concentrations in Mesopodopsis orientalis (Crustacea: Mysidae) with Regard to Its Life Stages and Sex in the Cochin Estuary, India

Trace metal concentrations with regard to certain life stages and sex of mysid species, &lt;i&gt;Mesopodopsis orientalis&lt;/i&gt;, from the Cochin estuary were studied during monsoon and pre-monsoon seasons. Spatially varying heterogeneous patterns of trace metal loads were apparent within the mature males, immature males, spent females, brooding females, immature females and juveniles of &lt;i&gt;M. orientalis&lt;/i&gt; for the region. The concentration ranges of trace metals like Fe, Mn, Zn, Pb, Cu, Cd, Ni, Cr and Co in &lt;i&gt;M. orientalis&lt;/i&gt; were: 590.5 to 1554.9 mg/kg, 4.1 to 15.1 mg/kg, 42.0 to 126.5 mg/kg, 2.5 to 17.0 mg/kg, 12.8 to 61.9 mg/kg, 0.2 to 2.3 mg/kg, 7.6 to 25.5 mg/kg, 8.8 to 33.4 mg/kg and 0.2 to 2.2 mg/kg, respectively. Higher metal concentrations were noted for the life stages of &lt;i&gt;M. orientalis&lt;/i&gt; during the monsoon season than in the pre-monsoon season. Mature males, immature males, spent females, brooding females, immature females and juveniles of &lt;i&gt;M. orientalis&lt;/i&gt; showed large variability in bioaccumulation for specific metals probably associated with distinct physiological processes. Juveniles and immature stages of &lt;i&gt;M. orientalis&lt;/i&gt; showed higher metal concentrations than adult organisms. High metal bioaccumulation and its spatial and seasonal variability with regard to animal life stages and sex suggest the importance of &lt;i&gt;M. orientalis&lt;/i&gt; as a biomonitor for tracing metal contamination in estuarine environments.

Length-weight relationship of twelve fin fish species from a Tropical Estuary

Length–weight relationships (LWRs) of twelve fish species: Planilizaplaniceps, Planilizaparsia, Etroplussuratensis, Pseudetroplus maculatus, Oreochromis mossambicus, Gerres setifer, Scatophagus argus, Escualosathoracata, Carangoidspraeustus, Caranxheberi, Deveximentuminsidator, Nuchequllablochiiwere examined from Cochin estuary. Fish were caught between March 2019 to February 2020 by various gears like ring seine (mesh size of 8–26 mm), smaller mesh sized drift gill net (26–90 mm), cast nets with a (15-20 mm). Fish were gathered weekly from Munambam Fisheries Harbour (Lat. 10°1029653N, Long. 76°1022583E), Cochin Fisheries Harbour (Lat. 09°5623273N, Long. 76°1527643E) and Chellanam (Lat. 09°4729503N, Long. 76°1625513E). There are significance in all LWRs with r2 values those are ranged from 0.92 to 0.99 and b values are ranged from 2.61 to 3.37 (p &lt; .001). The study provides new maximum length of E. thoracata.

Input-export fluxes of heavy metals in the Cochin estuary, southwest coast of India.

Cochin estuary (CE) is one of the largest tropical estuaries along the southwest coast of India, sustaining rich bio-resources. Several studies enlighten the environmental changes in the CE caused by anthropogenic activities. In the present study, an attempt has been made to quantify the heavy metal (dissolved and particulate) fluxes brought by the six rivers into the CE with their exchange into the coastal ocean through the major inlet at Cochin during a steady flow period (October-November 2015). The water flux across the inlet was quantified using an acoustic doppler current profiler. The measured daily input of dissolved metals from the rivers was 2.43 × 103kg Fe, 334kg Zn, 259kg Ni, and 83kg Cr, while that of particulate metals were 85.30 × 103kg Fe, 8. 6 × 103kg Mn, 236.9kg Cr, and 111.9kg Zn. The net export of metals through the Cochin inlet (per tidal cycle) was 3.3 × 103kg Fe, 515kg Cr, 150kg Zn, and 5kg Ni in dissolved form and 3.32 × 105kg Fe, 1747kg Mn, 1636kg Cr, 1397kg Zn, and 586kg Ni in particulate form. The high concentrations of metals during ebb tides are clear indications of their contribution from the industrial conglomerates (industrial units of metallurgy, catalyst, fertilizer, and pesticides) located in the Periyar River. The significance of this study is that the export fluxes may increase further during the summer monsoon (June to September), which may impact the abundant fishery emanating in the coastal environment during the period due to intense upwelling.

Surge in the jellyfish population of a tropical monsoonal estuary: A boon or bane to its plankton community dynamics?

Recurrent jellyfish blooms and their impacts on ecosystem deliverables of coastal habitats have become a major ecological concern. In view of this, repercussions of a surge in the jellyfish population on the plankton community were studied in Cochin estuary (CE), the largest tropical estuary along the southwest coast of India. Evaluation of hydrographic attributes and plankton community of the CE during early and late pre-monsoon revealed a marked disparity in its hydrography which favoured an increase in jellyfish abundances during late pre-monsoon, eliciting distinct impacts on the plankton community. The escalation in the jellyfish abundance and their subsequent predation on the crustacean plankton released the phytoplankton community from the grazing pressure resulting in a trophic cascade in the planktonic food web. The indiscriminate feeding of jellyfishes on the ichthyoplankton, decapod larvae, and Copepoda, the primary diet component of forage fishes evoked a potent threat to the fishery potential of CE.

Lipid biomarkers as organic matter source indicators of estuarine mangrove ecosystems

ABSTRACT Surface sediments from three mangrove forests and three adjoining stations of the Cochin estuary were analysed for lipid biomarkers along with bulk parameters to delineate organic matter (OM) sources. Fine-grained sediments dominated in mangrove forests due to low hydrodynamic energy conditions compared to estuaries. The protein/carbohydrate ratio >1 at most of the sites implied that a major fraction of OM was freshly originated. Lipid/carbohydrate ratios >1 indicated the better food quality of OM. Depleted δ13C, higher organic carbon-to-nitrogen ratios (>20), tannin and lignin content and lipid biomarkers implied OM inputs from mangrove vegetation. Occurrence of unique mangrove biomarkers like taraxerol in estuarine sediments reflected mangrove input via tidal export of OM. Prominent relative abundance of steroidal ketones, triterpenoid ketones and other degraded triterpenoids pointed towards active diagenetic transformations of sedimentary OM. Significantly higher content of biochemical components and biomarkers in mangrove systems was due to the dominance of fine-grained sediments and better preservation of OM under anoxic conditions. The study could provide baseline information on the significance of OM sequestration and preservation potential of mangrove ecosystems, and hence it is recommended to formulate sustainable management strategies to conserve the existing mangrove forest cover along the Kerala coast.

Evaluation of toxicological impacts of Polyvinyl Chloride (PVC) microplastics on fish, Etroplus suratensis (Bloch, 1790), Cochin estuary, India

Evaluation of toxicological impacts of Polyvinyl Chloride (PVC) microplastics on fish, Etroplus suratensis (Bloch, 1790), Cochin estuary, India

Feeding ecology, trophic interaction and resource partitioning among four omnivorous finfish species of a tropical Estuary

A crucial aspect of sustainable resource management is understanding the trophic interactions amongst fish in the estuarine ecosystem. The goal of this study was to look into the food preferences, feeding strategies, trophic partitioning, as well as dietary overlap among four omnivorous species that live in the Cochin Estuary: Mugil cephalus (n = 73), Planiliza parsia (n = 35), Planiliza planiceps (n = 65) and Chanos chanos (n = 55) through the analyses of gut-content. Index of relative importance demonstrated that prey items in Mugil cephalus and Planiliza planiceps guts were dominated by Bacillariophyceae whereas in Planiliza parsia and Chanos chanos guts were dominated by Myxophyceae. The highest diet value (7.5) was recorded in Chanos chanos, while the lowest was recorded in Mugil cephalus (5.69). The highest niche breadth value (0.77) was recorded in Planiliza planiceps while the lowest value was recorded in Planiliza parsia (0.52). Pianka's overlap, evaluated with the help of null models structured by Ecosim 7.0, showed remarkable niche overlap between Mugil cephalus and Planiliza planiceps (0–0.92, P &lt; 0.001), between Planiliza planiceps and Planiliza parsia ( 0–0.77, P &lt; 0.05) and between Mugil cephalus and Planiliza parsia ( 0–0.7, P &lt; 0.05). The fish's trophic niche width, along with prey-specific abundance confirmed that they are generalist feeders. The present results differed from the general hypothesis related to the omnivorous species and concluded that these four omnivorous species live in the same niche zones of the Cochin Estuary with no interspecific conflict.