Seasonal variation in fish diversity and feeding guild structure in Indrabati Dam, Odisha

Introduction

Inland freshwater reservoir ecosystems are among the most diverse and productive ecosystems on Earth. They play a vital role in maintaining biodiversity, ecological balance, and supporting human livelihoods. Reservoirs are man-made artificial ecosystems that provide many ecological functions such as nutrient cycling, habitat support, and societal benefits including fish production, hydroelectric power, irrigation, and drinking water supply (Wetzel, 2001) [1] . In India, large freshwater reservoirs associated with the monsoon period represent some of the most important inland fisheries, contributing significantly to fish production and providing livelihoods for many rural communities (Sugunan, 1995) [2] . The Indrabati Dam is located within the Indravati River basin in Nabarangpur district, Odisha. It is a multipurpose reservoir that supports fisheries, agriculture, and water storage. Despite its ecological and socio-economic significance, there is a significant lack of scientific data documenting the fish assemblages, seasonal fluctuations, and trophic structure in this reservoir. Understanding such systems is important because reservoirs are constantly subjected to physical, chemical, and biological alterations due to seasonal cycles, hydrological variability, and anthropogenic pressures. Tropical freshwater ecosystems possess marked seasonality. In India, distinct pre-monsoon, monsoon, and post-monsoon periods regulate water levels, nutrient inflow, habitat structure, and productivity (Jhingran, 1991) [3] . Hydrological changes affect key physicochemical parameters such as temperature, dissolved oxygen, turbidity, pH, conductivity, and nutrient concentrations, thereby determining the composition, distribution, and abundance of fish communities (Welcomme, 2001) [4] . Monsoon inflows enhance habitat complexity and plankton abundance, offering suitable conditions for planktivorous fish and allowing spawning of many indigenous species. The pre-monsoon period is often characterized by low water levels, high temperature, reduced dissolved oxygen, and heightened competition for resources. Fish diversity provides important insights into ecological integrity and environmental health of aquatic ecosystems. High species richness indicates stable habitat, functioning trophic networks, and high resilience, while declines in diversity or presence of only tolerant species may indicate ecological stress or habitat degradation (Karr, 1981; Dudgeon et al., 2006) [6,5] . The eastern Indian river basins, including Odisha, are areas of high biodiversity due to many endemic and native fish species (Sarkar et al., 2010) [7] . Similar patterns of seasonal environmental variation affecting aquatic communities have been documented in other river ecosystems (Dar et al., 2022; Ratnakar et al., 2024) [8,9] . In addition to species richness, feeding guild structure provides a functional ecological perspective. Feeding guilds categorize fish into groups based on feeding habits (herbivores, omnivores, carnivores, planktivores, detritivores, insectivores), which helps understand energy flow, trophic interactions, and ecosystem stability (Winemiller et al., 1998) [10] . Seasonal changes in food availability (plankton blooms, detritus buildup, insect emergence) can lead to significant shifts in guild dominance.Given this background, we designed this study with the following objectives:,To investigate fish species' seasonal diversity and composition in Indrabati Dam

Materials and Methods

Study area

The research took place in Indrabati Dam, located in the Indravati River basin, Nabarangpur district, Odisha. Four sampling stations were selected representing different areas of the dam: inflow into the reservoir, middle of the reservoir, near the dam, and a peripheral environment. Samples were collected over one full annual cycle (2025) covering three primary seasons: winter, summer, and monsoon.

Sampling design and frequency

We used a seasonal sampling design at each station during three seasons (winter, summer, monsoon). Three replicate samples for fish and three replicate water samples were collected per station per visit to provide within-station replication. Sampling effort was standardized for each gear type.

Fish sampling methods

A combination of gear types was used to sample different habitats and size classes:

Gill nets with mesh sizes 10 mm, 20 mm, 30 mm, 40 mm, and 60 mm set for 2 hours Seine nets (10-20 m length) with cod-end mesh sizes 1-5 mm for littoral areas Cast nets in shallow nearshore areas (3-5 throws per replicate)

Local catch surveys to complement field sampling

Field processing of fish

Fish were identified to species level using regional keys (Jhingran, 1991; Mogalekar, 2018) [3] . Representative specimens were photographed.

Feeding guild analysis

Stomach contents were examined under a stereomicroscope. Prey items were identified to the lowest feasible taxonomic level. The Index of Relative Importance (IRI) was calculated for each prey category:

Where N % = numerical percentage, V % = volumetric percentage, F % = frequency of occurrence. Trophic guilds (planktivore, detritivore, herbivore, omnivore, carnivore/insectivore) were assigned based on dominant food items.

Water quality analysis

Surface water samples (0.5 m below surface) were collected in clean, pre-rinsed polyethylene bottles. Temperature, DO, and pH were measured in situ using portable probes. Nutrients were analyzed in the laboratory. Three replicates were collected per station per visit.

Diversity indices

Margalef richness index = 𝑆 -1 ln 𝑁

Where π = relative abundance of ith taxon, S = total number of species, N = total number of individuals.

Results

Water quality parameters

Fish species composition

A total of 17 fish species belonging to 4 orders and 8 families were recorded. Cypriniformes was the most dominant order with 9 species (53% of total), which is typical for Indian freshwater ecosystems. Siluriformes ranked second with 4 species (23%), followed by Perciformes with 3 species (18%). Decapoda (prawn) contributed 1 species (6%). The dominance of Cypriniformes reflects their adaptability to a wide range of freshwater habitats.

Discussion

Our study recorded 17 fish species from 4 orders and 8 families in Indrabati Dam. The dominance of Cypriniformes (53%) is typical for Indian freshwater ecosystems. Cyprinids dominate because of their high adaptability, varied feeding strategies, and large reproductive capacity (Jayaram, 2010) [11] . Similar cyprinid dominance has been observed in other freshwater reservoirs across India (Sarkar et al., 2013) [12] . The presence of commercially important species like Labeo rohita, Catla catla, and Cirrhinus cirrhosus indicates the reservoir's fisheries potential. Water quality parameters showed clear seasonal patterns. Water temperature ranged from 21-32 °C, within the optimal range for tropical freshwater fish. Dissolved oxygen was lowest during summer (5.7-6.5 mg/L) due to higher temperatures reducing oxygen solubility, but remained above critical levels for fish survival. pH remained slightly alkaline (7.1-8.5) throughout the year, suitable for most freshwater fish species. Higher TDS, conductivity, nitrate, and phosphate during monsoon indicate nutrient input from catchment runoff. Similar patterns of seasonal environmental variation affecting aquatic communities have been documented in other river ecosystems (Dar et al., 2022; Ratnakar et al., 2024) [8,9] . Fish diversity was highest during winter at Station 2 (Shannon H = 2.079) and Station 2 during monsoon (Shannon H = 2.379). High diversity during winter can be attributed to stable water conditions, lower temperature stress, and adequate food availability. The high diversity during monsoon reflects increased water levels, habitat expansion, and nutrient input supporting primary productivity. Station 2 (middle of the reservoir) consistently showed the highest diversity, likely due to good riparian vegetation providing nutrient sources and well-balanced habitat substrate (Legendre, 1998; Medupin, 2020) [13,14] . The lowest diversity was recorded at Station 4 during summer (Shannon H = 0.581). This station likely experiences higher anthropogenic pressure, lack of riparian vegetation, and poorer habitat qual-ity (Patang et al., 2018) [15] . Summer conditions (high temperature, low water level, reduced DO) further stress fish populations, leading to lower diversity. The trophic guild analysis revealed a balanced ecosystem with carnivores (47%), omnivores (29%), detritivores (12%), and planktivores (12%). The presence of top predators like Channa marulius and Sperata seenghala indicates a healthy food web. Detritivores like Cirrhinus cirrhosus play important roles in nutrient recycling. Planktivores like Catla catla help control plankton populations. This functional diversity contributes to ecosystem stability and resilience (Winemiller et al., 1998) [10] .

Conclusion

This one-year study assessed seasonal variation in fish diversity, water quality, and feeding guild structure in Indrabati Dam, Odisha. A total of 17 fish species belonging to 4 orders and 8 families were recorded. Cypriniformes dominated with 9 species (53%), followed by Siluriformes (4 species, 23%), Perciformes (3 species, 18%), and Decapoda (1 species, 6%). Water quality parameters showed clear seasonal patterns: temperature (21-32 °C), pH (7.1-8.5), DO (5.6-8.0 mg/L), and TDS (178-290 ppm), with higher nutrient levels during monsoon due to catchment runoff.

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16. How to cite this article: Panda A, Mishra R, Saxena S. Seasonal variation in fish diversity and feeding guild structure in Indrabati Dam, Odisha. International Journal of Veterinary Sciences and Animal Husbandry. 2026;11(9):31-35. doi: https://www.doi.org/1