Experimental Gill Nets Research Articles

Comparisons of oxbow lake fish assemblages in relation to bigheaded carp establishment in the lower White River, Arkansas

BackgroundSince the late 1990s, bigheaded carps (largely silver carp [Hypophthalmichthys molitrix] but also bighead carp [H. nobilis]) have established throughout the lower Mississippi River basin. Using previously studied oxbow lakes in the lower White River basin, Arkansas, we compared current (2017, “post-carp” establishment) fish assemblages to historical (2002, “pre-carp” establishment) fish assemblages. Fish assemblages were comprehensively assessed using multiple gears, including boat electrofishing, mini-fyke nets, and experimental small-mesh gill nets.ResultsT-tests suggested that fish assemblage indices of richness, diversity, evenness, and dominance were often greater (P < 0.05) during the post-carp period as reflected by boat electrofishing and experimental gill nets. However, all indices were generally similar (P > 0.05) between the pre-carp and post-carp period with fish assemblages depicted using mini-fyke nets. Nonmetric multidimensional scaling analyses indicated that fish assemblages differed structurally between pre-carp and post-carp periods. Assemblage differences were linked to both small and large abundance changes for more than 20 species. Abundances of gizzard shad (Dorosoma cepedianum), emerald shiner (Notropis atherinoides), pugnose minnow (Opsopoeodus emiliae), crappies (Pomoxis spp.), bluegill (Lepomis macrochirus), orangespotted sunfish (L. humilis), and yellow bass (Morone mississippiensis) declined between the pre-carp and post-carp periods. Conversely, abundances of weed shiner (N. texanus), pallid shiner (Hybopsis amnis), longear sunfish (L. megalotis), buffalofishes (Ictiobus spp.), and gars (Lepisosteus spp.) generally increased during the same period.ConclusionsAlthough not possible to conclude assemblage shifts were entirely related to bigheaded carps due to the absence of an appropriate reference system where carps did not establish, the wide establishment of these carps is one of the most pervasive changes to have occurred in the lower White River ecosystem during the past two decades. Thus, it is probable to conclude that post-carp establishment observations from this study were at least, in part, attributable to bigheaded carp establishment. Impacts of further range expansions by bigheaded carps in the White River and other lower Mississippi River sub-basins are unclear, though this study suggests probable effects on native fish assemblages, underscoring the need for further research and monitoring.

Species Composition and Abundance of the Cichlid Fishes in Owalla Reservoir, Osun State, Nigeria

Fish production plays crucial roles in enhancing food security and alleviating poverty of many people in Nigeria. As demand for fish increases steadily over the years, production becomes inadequate. One of the ways in which adequate fish production could be met is adequate conservation efforts. This study was conducted with a view of providing a more recent catalogue and update of species composition and abundance of cichlid fishes in Owalla reservoir. Sampling for cichlids fishes in the reservoir was done monthly for 24 weeks with the use of dugout canoe. Four experimental gillnets, each measuring 2 by 30 m, with various stretched mesh sizes (25.4, 38.1, 50.8 and 63.5 mm) were designed to sample various sizes of the fishes. Other sampling techniques adopted include the use of cast net, fish traps and hook and line. The six species of cichlid fishes identified during study are Hemichromis fasciatus (SL=7.35±0.12 cm; mean weight=15.58±9.01g), Sarotherodon galilaeus (SL=11.77±3.12 cm; mean weight=89.48±14.17 g), Oreochromis niloticus (SL=8.35±1.90 cm; mean weight=36.11±10.02 g ), Tilapia zilli (SL=9.95±1.09 cm; mean weight=88.03±16.04 g ), Tilapia mariae (SL=9.83±1.07 cm; mean weight=57.81±14.01 g ) and Tilapia dageti (SL=11.12.±2.01 cm; mean weight=85.30±20.01 g). The fish species were adequately represented, well distributed and occurred frequently in both wet and dry seasons, though the occurrence was higher in the wet season. The mean values of length and weight recorded for the fishes were small when compared with the values of cichlids from similar Nigerian inland waters and was attributed to the indiscriminate use of gillnets with unregulated mesh sizes. Overfishing by the artisanal fishermen could not be ruled out due to lack of regulations on the reservoir. Therefore, regular qualitative and quantitative information on cichlid fishes in the reservoir is necessary for enhancement of management and appraisal of the fisheries potential of the reservoir becomes essential.

Ecophenotypic Variation of Midas Cichlid, Amphilophus citrinellus (Gunther, 1864), in Lake Batur, Bali, Indonesia.

Cichlid fishes exhibit rapid adaptive radiations with significant diversification rates in response to ecological variability, i.e., ecological opportunity or geographical isolation. The discovery of a Midas cichlid species in Lake Batur, Indonesia's largest volcanic lake, first reported in 2013, could represent such adaptations. Midas cichlids can now be found in a range of habitats in Lake Batur and dominate the lake's fish population by up to 60%. This study aimed to identify the interaction between habitat, water quality, and Midas cichlid in Lake Batur, facilitating morphometric variances in the fish populations. The fish were captured at five locations in Lake Batur using fishing rods, community nets with mesh sizes of 2-3 inches, experimental gillnets with mesh sizes of 1 inch, and fish scoops in floating net cages during August and November 2022. There were 46 fish samples caught from the five stations, all photographed using a digital camera and later measured using the ZEN 2012 software. The fish measurement employed a truss morphometric method using 21 distinct morphometric body features. Canonical analysis was used to determine the distribution of characteristics, while discriminant analysis was used to examine the closeness of association. The measured water quality parameters included pH, DO, temperature, conductivity, and TDS for in-situ and TSS, TP, TN, and chlorophyll A for ex-situ. The findings revealed morphometric changes among Midas cichlid species in Lake Batur caused by habitat and water quality differences. The distinction can be detected in the anterior and posterior bodies (C1, B1, C3, C6, C5, B3 and B4). Temperature and aquatic plants, Azolla pinnata, may detect the station and shape of fish in Lake Batur. Body shape cannot be identified by chlorophyll A, TN, DO, and TDS. Future genetic research could answer why fish groups with varied body types coexist in the same location.

Characterization of fish assemblages in eleven multi-use reservoirs from North Carolina, USA

Managing impounded river systems is a recurring challenge for aquatic resource professionals because reservoirs serve multiple functions with different ecological and socioeconomic outcomes. However, research on fishes in reservoirs has disproportionally focused on recreationally and economically important species, with less attention directed toward fish assemblages despite the potential for management at the assemblage level. As such, evaluation of relationships between reservoir fish assemblages and biotic and abiotic factors and testing whether assemblage structure is affected by changing environmental conditions may deepen ecological understanding and provide insights for reservoir fisheries management. Our overall objective was to assess these relationships in 11 reservoirs from North Carolina, USA. We sampled fish assemblages in the reservoirs, which spanned five river basins representing a range of habitat conditions, using experimental gillnets and pulsed DC nighttime electrofishing. Multivariate statistical analyses indicated that taxonomic differences in fish assemblage composition among river basins followed a gradient of productivity. The top contributing species to reservoir dissimilarity were bluegill (Lepomis macrochirus), gizzard shad (Dorosoma cepedianum), black crappie (Pomoxis nigromaculatus), and white perch (Morone americana). These four species were positively associated with factors that reflect increasing eutrophic conditions in the 11 reservoirs and could, therefore, serve as indicators of reservoir productivity, anthropogenic influence, and fish assemblage structure, in addition to their key role in reservoir fisheries management. Whereas ­fisheries research has historically focused on assessing fish ­populations, our results illustrate the ecological and management insights derived from simultaneously collecting assemblage- and population-level data. Research on reservoir fish assemblages in relation to biotic and abiotic conditions may help advance fish ecology and management alike.

Investigations on depredation by the deepsea swimming crab Charybdis smithii, during experimental gillnetting along the south-west coast of India

Depredation by crabs can have a negative impact on marine gillnet fishery. Despite this fact, limited studies are attempted to evaluate depredation. The present study is the first attempt to evaluate the qualitative and quantitative effects of crab depredation on marine gillnet fishery. Experimental gillnetting was conducted onboard F V Sagar Harita from February 2017 to January 2018 along the south-west Indian coast. Depredation by the deepsea swimming crab Charybdis smithii caused intentional discard of Indian mackerel (17.59%), kawakawa (14.77%), shrimp scad (10.74%) and horse mackerel (10.02%). Financial loss due to depredation was high for Indian mackerel (19.99%), followed by shrimp scad (19.17%), kawakawa (14.77%) and horse mackerel (14.16%). A total of ₹2554.30 per operation was lost due to crab depredation. C. smithii showed a preference towards scombrids (Indian mackerel and kawakawa) over carangids (shrimp scad and horse mackerel) due to the inherent flavour and texture of scombrids. Incidence of depredation were found exclusively during June to September (monsoon season). Keywords: Crab, Depredation, Economic loss, Fishery, Marine gillnet

Seasonal Variation of the Ecological Water Quality in a Drinking Water Supply Dam Lake in Bongouanou (Côte d’Ivoire)

The Ichthyological Index of Wetlands (IIW), for the monitoring of the water quality of Ehuikro Lake in Bongouanou, was established. Monthly, experimental gillnet fisheries were conducted between July 2017 and June 2018 in Lake Ehuikro (Bongouanou, Ivory Coast). The fish collected were identified and counted each month, as well as the physicochemical parameters measured in-situ. A partial canonical correspondence analysis (pCCA) was used to order fish species along the axes according to physicochemical parameters to explain anthropogenic disturbances. It appears from this analysis that the water of Lake Ehuikro is of "good quality" during the rainy season and of "poor quality" during the dry season.

The The Effect of Using Led Lights (Light Emitting Diode) in the Operation of Bottom Gillnets on Catches In Pangandaran Waters, West Java

The objectives of the study were to analyse the response of dominant fish to different light colours that reflect the wavelength of light and to analyse the species composition of the gillnet catch to determine the fish that are positively phototaxis to LED light. Data collection was conducted using the experimental method. The experimental design used 1 unit of bottom gillnet gear with a mesh size of 4 inches, and used LED (Light Emitting Diode) lights. Trials using green LED lights and white LED lights were operated simultaneously between the control gillnet (without LED lights) and the experimental gillnet (with LED lights). The results of statistical analysis of gillnet catches with green LED light aids with white LED light aids and control nets have a significant effect on the number of gillnet catches. The results were: (1) The number of fish caught at a distance of &lt; 1 m and at a distance of 1-2 m, this proves that many fish are attracted to light (positive phototaxis); (2) Proven by gill net fishing gear using green LED light aids obtained fish weighing up to 77.7 kg. (3) It is proven that the distance of the lamp with the position of the fish caught on the net sheet can produce the highest weight of fish caught, on green LED lights at a distance of &lt;1 m the weight of the fish reached 30.89 kg.

Experimental Mixed Gillnets Improve Catches of Narrow-Barred Spanish Mackerel (Scomberomorus commerson)

A new gillnet made from multiple mesh sizes ranging from 125 to 180 mm of stretched mesh (experimental gillnet) was tested under commercial fishing conditions to compare the fishing performance with that of conventional gillnets with a 125 mm mesh opening (control gillnet). Catch efficiency and size selectivity between the two gillnet types were evaluated throughout one year of fishing in three different locations in the waters of Vietnam. Experimental gillnets caught narrow-barred Spanish mackerel (Scomberomorus commerson), spotted mackerel (Scomberomorus guttatus), and wahoo (Acanthocybium solandri) in comparable amounts to the control gillnets, with the moon phase, month, and depth explaining some of the variation in the catch per unit effort (CPUE). An analysis of the size-dependent catch comparison rates and selectivity parameters showed that the experimental gillnets captured a wider range of narrow-barred Spanish mackerel sizes, but with a substantial proportion of individuals larger than those caught by the control gillnets. This is of higher weight per unit effort, and fishing enterprises therefore could improve their economic benefits by using modified gillnets with multiple mesh sizes. Our findings also support the biological and environmental benefits of the modified gillnet size selection, which might also extend to other species.

Ghost fishing capacity of lost experimental gillnets: a preliminary study from Indian waters.

Abandoned, lost, or otherwise discarded fishing gear contributes considerably to global marine debris. These lost gears, mostly made of non-biodegradable synthetic materials, persist in the marine environment for longer periods of time and pose a great threat to marine life by entangling and killing target fishes and other non-target species such as turtles, birds, and mammals, a phenomenon known as ghost fishing. Other environmental impacts include physical impacts on aquatic habitats, transfer of microplastics into food web, and interference with fishing. Information regarding the catching efficiency and catch rates of lost nets in Indian waters is lacking. Ghost fishing capacity of simulated lost gillnets is being reported for the first time in India. This study investigates the ghost fishing capacity of lost gillnets through an experimental approach at Aroor, Vembanad lake, Kerala, India. Simulation studies using purposefully abandoned shrimp gillnets (32mm mesh size) were conducted to understand the fishing capacity of lost gillnets during two seasons (monsoon and post-monsoon) as separate experiments. The gillnets maintained their catching efficiency until the 15th day during the first experiment and up to the 50th day in the second experiment. Catches showed an exponential reduction over time in both experiments. A total of 251 specimens comprising of 27 species were caught from both sets of experimental nets, and the state of catch in the nets showed different decaying stages from the second day itself along with fresh stages. As the days progressed, particulate matter and detritus began to accumulate on the experimental nets, increasing net visibility and reducing their catching efficiency. The results of the study on ghost fishing capability will contribute to the development of strategies for reducing the effects of lost nets on the aquatic ecosystem and for suggesting improved management strategies.

Ichthyo-diversity of Batur Lake, Bali: A preliminary study

Batur Lake is the largest lake on Bali Island. Batur Lake has various potential fish resources. This study aims to determine the diversity of fish in Batur Lake waters. The research was conducted from November to December 2021. The method used in this research is the purposive sampling method. Using experimental gill nets, the samples were collected at the three stations covering Toya Bungkah, Seked, and Kedisan waters. The results showed that 516 individual fish comprised native and alien species. Native species were Osteochilus vittatus, Barbodes binotatus, Barbonymus gonionotus, Barbonymus balleroides, and Rasbora lateristriata; the others were alien species (7 species). Furthermore, based on the literature study, one of the native species that was collected is included in the IUCN red list with a vulnerable (VU) status, namely Rasbora lateristriata. Ichthyofauna in Batur Lake consisted of four orders, four families, and 12 species from native and alien species. The dominant species collected was alien species (Amphilophus citrinellus and Xiphophorus hellerii), while the one native species was Barbonymus balleroides. The highest values of diversity and uniformity indexes were found in Seked and Kedisan waters; meanwhile, the highest dominance index was found in Toya Bungkah waters.

Morphoregression and Reproduction Aspect of Bonylip Barb (&lt;I&gt;Osteochilus vitattus&lt;/I&gt; Valenciennes, 1842) in Tamblingan Lake, Bali Island

Highlight Research Morphoregression and reproduction aspect of bonylip barb was analyzed Fork length more accurately to estimate the body weight Lm50 of bonylip barb in Tamblingan Lake was 116 mmTL Growth pattern is isometric Good reproduction aspect Abstract Bonylip barb (Osteochilus vitattus Valenciennes, 1842) is one of many native fish inhabiting Tamblingan Lake. The information about this species in Tamblingan Lake is rare which requires fulfilment in information gaps for the management of bonylip barb. The aims of this research were to find out the length-length relationship, length-weight relationship, length at first maturity, sex ratio, gonadal maturity stage, gonadosomatic index (GSI), fecundity, as well as spawning period and location in Tamblingan Lake. The fish sample was captured with experimental gillnet that was set in the afternoon and hauled in the next morning. Length and weight of every sample were taken. All samples were dissected to observe the sex and gonad. Fork length was the type of length with higher accuracy to estimate the body weight than the other length character. Growth pattern of this species was isometric. Lm50 of bonylip barb in Tamblingan Lake was 116 mmTL. Sex ratio of bonylip barb was imbalanced (1.00:0.82). Gonad maturity stage I-V was found during the research with GSI between 0.16-15.50 for male fish and 0.43-32.82 for female fish. The highest GSI was found in March, 15.50 for male fish and 32.73 for female fish. Mature fish were discovered in all stations in every month of sampling. The fecundity of bonylip barb ranged between 2,792-279,326 eggs. The length-length and the length-weight showed a strong relationship. The fish was isometric. Based on the growth pattern and the reproductive aspects, the population of bonylip barb in Tamblingan Lake was in good condition.

Size distribution and length-weight relationship of invasive species flowerhorn (Cichlasoma trimaculatum (Günther, 1867) in Lake Mahalona, South Sulawesi

Lake Mahalona is one of the lakes located in the Malili Complex, South Sulawesi and is included in the Natural Tourism Park Area. Cichlasoma trimaculatum are ornamental fish from the Cichlidae family that become invasive in Lake Mahalona. A total of 29 fish species were recorded in this lake, and most of them are endemic fish. It is estimated that native and endemic fish species and populations will decline due to invasive alien species intentionally or unintentionally in Lake Mahalona. The study to determine the size distribution and length-weight relationship of C. trimaculatum was conducted in Mahalona Lake. The study was conducted at 11 stations in October 2020. Experimental gill nets used to catch Bilih. The total length of C. trimaculatum ranged from 10.0 ± 1.57 cm (Kusapa and Badilla stations) to 18.0 ± 1.57 cm (Benu station), and the weight ranged from 19.0 ± 19.2 g (Kusapa station) to 140.0 ± 19.2 g (Muara station). The correlation coefficient (r) value for this fish ranges from 0.8685 - 0.9691. The growth pattern of C. trimaculatum was a negative allometric characteristic. An exception in Muara dan Tandu Mata stations was positive allometric.

Distribution and Habitat Characteristics Of Endemic Fish Bilih (Mystacoleucus padangensis Blkr.) In Lake Singkarak, West Sumatra

Lake Singkarak is one of the volcanic lakes in Solok Regency, West Sumatra Province. Bilih (Mystacoleucus padangensis) is an endemic fish species and has important economic value in Lake Singkarak. Concerning will be occured degradation of the fish population in nature due to change of environment and intensive fishing. The aim of this research to obtain information on distribution and habitat characteristics of endemic fish Bilih in Lake Singkarak on May 2021. The fish captured with experimental gillnet mesh size 0.625; 0.75; and 1.0 inches at four stations. The number of Bilih fish caught during the study was 521 fish, most were found at Sumani station was 332 fish with a grain value of 45% sand, 37% silt, and 18% clay. The highest average length of male and female Bilih were 77.9 and 80.7 mm, and the highest average weight size of male and female fish was 41 and 46 mg, respectively, which was found at Sumani station. The highest GMS IV Bilih were found at Sumani station and at Paninggahan station dominated GMS III. The length and weight of male Bilih in GMS IV were the highest at 77.3 mm and 42 mg as well as female Bilih in GMS IV were at 80.6 mm and 46 mg at Sumani station. Bilih are distributed in all stations in the waters of Lake Singkarak. In general, the measurement results of water quality in Lake Singkarak during the study ranged from 27.87 – 28.91 °C for temperature, pH 8.59 – 9.24, Dissolved Oxygen ranged from 4.56 – 7.02 mg/L, Oxidation Reduction Potential ranged 30 – 155 mV, Conductivity ranges from 0.137 – 0.145 mS/Cm, Total Dissolved Solid ranges from 0.089 – 0.093 mg/L and the Sechi depth ranges from 2.27 – 3.78 meters.

Gill Net Selectivity for Fifteen Fish Species of the Upper San Francisco Estuary

Gill-net size selectivity for fifteen fish species occurring in the upper San Francisco Estuary was estimated from a data set compiled from multiple studies which together contained 7,096 individual fish observations from 882 gill net sets. The gill nets considered in this study closely resembled the American Fisheries Society’s recommended standardized experimental gill nets for sampling inland waters. Relationships between gill-net mesh sizes and the sizes for each fish species retained in them were estimated indirectly using generalized linear modeling and maximum likelihood. Selectivity curves are provided for each species to inform researchers about population characteristics of fishes sampled with similar gill nets.

Assessing the catch efficiency of predators in the presence of prey using experimental gillnets in a temperate estuary

Fishery-independent sampling is designed to representatively sample faunal communities based on the effort-standardized catch rates of individual gears. In estuaries, experimental gillnets are widely used due to their ability to passively sample mobile fish communities with multiple panels of decreasing mesh sizes. To test if concurrently collected prey in experimental gillnets create a trophic-related sampling bias for predatory or scavenging (hereafter, predators) species, we set large mesh gillnets comprising two treatments, baited (n = 80) and unbaited (n = 78), using a paired design in Back Sound, North Carolina. Furthermore, we analyzed data from the North Carolina Division of Marine Fisheries (NC DMF) estuarine gillnet monitoring program with boosted regression tree models to correlate estuarine predator occurrence with environmental factors (salinity, temperature), habitat presence, and families of common prey species as predictor variables. In our experimental manipulation, neither total catch nor community composition statistically varied between treatments, determined using permutational multivariate analysis of variance (PERMANOVA). However, species richness estimated using species accumulation curves was higher in baited gillnets, with one frequently caught species (Atlantic sharpnose sharks) collected exclusively in baited gillnets. In NC DMF surveys, prey group variables were more important (average model importance; 10% ± 8.8% SD) than habitat composition (2% ± 1.7%) to the presence of predators, but less than abiotic environmental variables (21.1% ± 13.1%). This combined manipulative and mensurative study revealed mixed evidence towards increased catch efficiency of predatory fish collected in widely used experimental gillnets. These results should be considered in refining abundance estimations for estuarine predators, as catch efficiency for some piscivorous predators may vary in relation to the abundance and catch efficiency of prey.

Does Moon Phase Affect Indices of Kokanee Size and Abundance as Characterized by Gill‐Net Catch?

AbstractMany pelagic fish species such as kokanee Oncorhynchus nerka undertake diel vertical migration in response to dynamic interactions between ambient light, foraging opportunity, and predation risk. Consequently, kokanee populations are almost universally sampled during the dark phase of the moon (i.e., the new moon), presumably to optimize capture efficiency. However, it is unclear if this sampling precaution is necessary to avoid bias in kokanee catch data related to the moon phase. We used experimental gill nets to sample kokanee populations in two thermally stratified reservoirs during three distinct moon phases (i.e., new, first quarter, and full) to understand the relative effects of moon phase and other ambient light variables on total catch and average size of captured kokanee. The total catch of kokanee differed significantly between populations but was not significantly affected by moon phase, secchi depth, or net depth. The average size of kokanee sampled from both populations increased significantly with moon illuminance and likely reflects behavior associated with predator–prey dynamics. Results from this case study suggest that the effect of moon phase and other ambient light variables on gill‐net catch composition of kokanee is likely population‐specific and is governed in part by population parameters such as abundance, growth rate, and size‐structure. As such, investigators should be cognizant of—or perhaps standardize gill‐net samples to—ambient light variables when indexing populations of kokanee and other pelagic fishes that undertake diel vertical migrations, especially when size indices are examined.

Water hyacinth (Eichhornia crassipes) infestation cycle and interactions with nutrients and aquatic biota in Winam Gulf (Kenya), Lake Victoria

AbstractLake Victoria, like many other lakes in Africa, is affected by water hyacinth that reside in several bays for the majority of the year. The weed affects several economic activities of the local communities and denies revenue to the government from blue economic activities related to the lake. The present study examined the interaction of water hyacinth with biotic and abiotic factors and the efficiency of introduced weevils to better control this invasive weed. Water quality samples were collected and compared from the time of water hyacinth re‐emergence and sinking within the Winam Gulf of Lake Victoria. The present study was divided into three phases with an interval of 2 months. Water hyacinth was collected, and the damages resulting from the weevils to the hyacinth, as well as the number of weevils, was recorded and analysed. Fish samples were collected with experimental gill nets. The collected water samples was analysed for the aquatic plant nutrient ammonium, soluble reactive phosphorus, nitrates and nitrites. Data were analysed using R package. The results of the present study indicated that the weevils inhibited nutrient uptake by hyacinth by 17% within the first 4 weeks. The hyacinth subsequently increased the nutrient levels in the gulf by threefold after their decay and sinking. Weevils also increased the sinking rate of water hyacinth through the destruction of their petioles and leaves. One hundred and ninety‐four more fish were observed in the experimental nets during the weed infestation, compared to periods when the weed was absent within the gulf. The major conclusions were that water hyacinth impacts both biotic and abiotic factors, and that the weevils alone are unable to eradicate the weed.

TROPHIC INTERACTIONS OF THE FISH COMMUNITIES IN CIRATA RESERVOIR, WEST JAVA

The utilization of food resources by the fish communities in the Cirata Reservoir depends on the environmental conditions of the reservoir. Eutrophication and the presence of potentially invasive alien fishes could affect the trophic interactions of food utilization by the fish communities in the Cirata reservoir. This study aimed to analyze the trophic interactions of the fish communities in the Cirata Reservoir, West Java. The samplings were conducted in October, December 2018, and April 2019. The fish samples were collected using experimental gill nets with different mesh sizes. The stomach contents were dissected to study their food habits under a stereoscopic microscope. Data analysis was performed using the index of preponderance, niche breadth, trophic level, and index Schoener. A total of 21 species of fishes in the Cirata Reservoir utilized food resources, including phytoplankton, zooplankton, aquatic plants/macrophytes, molluscs, insects (adult and larvae), worms, a body part of fishes and crustaceans, pellets and detritus. The fish communities had a wide range of niche between 0.00-0.32 and trophic levels between 2.00-3.63. The non-native fishes in the Cirata Reservoir had the food overlapping potential with native fishes, from low to high categories, especially from the Cichlidae. Trophic interaction of fish communities in the Cirata reservoir was still relatively stable, characterized by overlapping food niche in the low to medium categories. The fish stock enhancement effort such as fish introduction or restocking in the Cirata Reservoir could still be carried out with a precautionary approach to filling empty niches and avoiding the potential for invasive alien fish species.

Reproductive traits and spawning activity of striped eel catfish (Plotosidae) in Kolono Bay, Indonesia

Abstract. Asriyana A, Halili H. 2021. Reproductive traits and spawning activity of striped eel catfish (Plotosidae) in Kolono Bay, Indonesia. Biodiversitas 22: 3020-3028. Reproduction is a natural process for a species to ensure its sustainability in nature. This study aimed to investigate the reproductive traits and spawning activity of the striped eel catfish in Kolono Bay, South Konawe District, Southeast Sulawesi, Indonesia. A total of 965 individuals were collected monthly from June 2020 to May 2021 by using bottom experimental gillnets. Spent/spawning stages of the male and female fish were found during the East season (June-August). The proportions of the spent/spawning stages of male and female fish were 60% and 55.56% and the values of the gonadal somatic index were 1.19 ± 0.53 and 2.19 ± 3.47, respectively during the East season, indicate occurring the peak spawning in this season. Females matured gonads more rapidly at 198.3 mm compared to males at 224.5 mm. Female fecundity was 1,730 ± 390 eggs, with an egg diameter of about 0.11-1.35 mm. Striped eel catfish is a total spawner fish that has one mode of egg distribution pattern. During the East season, it needs protection for spawning. The findings will help in designing effective management and developmental strategies to conserve the striped eel catfish population in the future.

Introduced fish species and their characters in Lake Maninjau, West Sumatra

The diversity of indigenous fish species in Lake Maninjau has been declining with the rise of local people’s activities. One of the causes is the invasive species, which are initiated by introduced species. This study aims to discover the species, distribution, growth pattern, and condition factor including information of the environmental condition, supporting the existence and growth of introduced fish species in Lake Maninjau. Sampling was conducted at four locations in Lake Maninjau; Bayur, Linggai, Sigiran, and Galapung. Fishes were collected by experimental gillnet which vary in mesh size, 0.5; 0.75; 1; 1.5; 2; 3; and 4 inches. These nets were set about 12 hours from 8 pm to 8 am on the next day, once a month in May, July, August, September, and October 2017. Four introduced fish species were observed and examined; there were Cichlasoma trimaculatum (Three-spotted cichlid), Oreochromis niloticus (Tilapia), Pterygoplichtys pardalis (Armored Catfish), and Oxyeleotris marmorata (Marble Goby). O. marmorata and O. niloticus were recorded at all of the sampling locations. C. trimaculatum was recorded in Galapung and Sigiran, while P. pardalis only found in Bayur. These dominant fish species have growth patterns each; there are negative allometric (O. marmorata), isometric (C. trimaculatum), and positive allometric (O. niloticus). Moreover, these three fish species have an almost 1.00 condition factor; there were 0.988, 1.024, and 1.001, respectively. Results and discussion infer that introduced fish species in Lake Maninjau were distributed at several locations with good growth and condition.