Net Mesh Size Research Articles

Gillnet selectivity of commercially important fish Labeo rohita, Hamilton,1822 and Catla catla, Hamilton,1822 in kosi river, Madhepura, Bihar

Application of fishing gears in fishery is the result of experiences gained over a long period of time. Every water body has a unique pattern of fishing activity. The present study was aimed to evaluate the selectivity of gillnets and the size at first maturity of commercially important fish species in Kosi river mainly the Rohu Labeo rohita and Catla Catla catla. Experimental fishing was conducted using gillnets of different mesh sizes (60, 80, 100, 120 and 140 mm) in six sampling occasions from 2023 - 2024. A total of 2671 fish specimens consisting of 1184 L. rohita and 1523 C. catla were analyzed. Gillnet selectivity parameters for each mesh sizes were estimated for each species using the SELECT method. The size at first maturity (Lm) and its 95% CI for L. rohita and C. catla were estimated at 23.9 cm (23.3 - 24.5 cm), and 32.5 cm (31.6 - 33.4 cm), respectively. Results showed that a Log-normal model best described gillnets selectivity for C. catla, while a Normal location model best described for L. rohita. Capture probability estimates indicate that the optimum length of capture (LCAP) of > 80 mm mesh size nets are smaller than the Lm of both target species, while LCAP of >120 mm mesh net selects above the Lm value for both L. rohita and C. catla. Although the 100 mm mesh selects above the size of Lm value for L. rohita, it still selects below the Lm value for C. catla. Based on the results obtained, it was concluded that gillnets of mesh size 100 and 120 cm may safely be applied in Kosi river fishery if proper level of effort is applied that ensures sustainability of both target species. This study provides the baseline scenario for formulating a sustainable fisheries management strategy since many aspects of the L. rohita and C. catla fishery are not disclosed.. KEYWORDS :Rohu, Catla, optimum length of capture, SELECT model, gonad maturity, Gillnet.

Classification of the Penguluran River and Mbambang River using Macroinvertebrate with TWINSPAN Analysis

The Penguluran River and Mbambang River are strategic rivers from an ecological, economic, and social perspective. In the last 5 years there have been flood disasters which can affect the communities within them, for example macroinvertebrates. The aim of the research is the classification of macroinvertebrate habitat groups in Penguluran River and Mbambang River. Research methods uses survey methods and secondary macroinvertebrate data in 2023. Sampling at 25 sites based on different land uses by kicking technique with a hand net (mesh size of 500 μm) in a 10 meter long riffle area. Data analysis using TWINSPAN (Two-way Indicator Species Analysis). TWINSPAN analysis obtained 9 site of group from 25 observation sites (site of groups A–I). Furthermore, the 9 site groups were divided into 3 large groups based on the level of macroinvertebrate sensitivity. Site of group E and F in Argotirto Village and Sumberagung Village have light sensitivity (30%) higher than medium sensitivity (20%) with current vellocity ranges medium to fast, rock and gravel substrates that experience light smoothering, plantation land use (coffee, mangosteen, and cloves) showed light degradation. Site of group A, B, C, H, and I in Argotirto Village, Sumberagung Village, and Sidodadi Village have moderate sensitivity (30%) higher than light sensitivity (20%), current velocity ranges slow to fast, rock substrate and gravel that experienced moderate smoothering, secondary forest land use, plantations (sugar cane, coffee, banana), settlements, and livestock showed moderate degradation. Site of group D and E in Argotirto Village and Sumberagung Village have tolerant sensitivity (36%) than sensitive macroinvertebrates (28%), current velocity ranges medium to fast, rock and mud substrates that experience heavy smoothering, plantation land use (coconut , banana, clove and mangosteen) showed heavy degradation. TWINSPAN analysis of 9 site of group shows light degradation, moderate degradation, and heavy degradation.

Chironomid Pupal Exuviae Technique in Ecological Research of Man-Made Water Bodies

Reservoirs serve functional purposes such as irrigation and power generation. However, concerns are raised due to the alterations of the connected riverine ecosystems. Chironomidae (Diptera), a diverse aquatic macroinvertebrate group, are vital to the functioning of ecosystems and serve as water quality indicators. Their holometabolous development includes the pupal stage after four larval stages. The chironomid pupal skin (exuvia) is used in environmental assessments, where the Chironomid Pupal Exuvial Technique (CPET) is a recognized standard. The CPET method is adaptable to different freshwater environments and here was applied in the study of 28 man-made lakes in the Pannonian Lowlands and Dinaric Western Balkan Ecoregion in Croatia to obtain information on chironomid diversity and analyze the potential influence of environmental factors on the chironomid community. The lake surface was skimmed with an exuvial hand net (mesh size of 300 µm) along the lake edge with a transect length of 10 m in the area of accumulated debris of organic and inorganic matter. Individual exuviae were mounted in a Berlese mounting medium and identified by morphological characteristics to the lowest taxonomic level. During the study, 5698 chironomid pupal skins were collected, and 141 taxa (including 97 species) belonging to five subfamilies were identified. The tribe Tanytarsini comprised 40% of the identified taxa, with Paratanytarsus spp. being the most abundant. In the Dinaric ecoregion, Paratanytarsus bituberculatus dominated, while Microchironomus tener and the genus Cricotopus were the dominant taxa in the Pannonian ecoregion. Community structure in the Pannonian ecoregion was influenced by total organic carbon (TOC) and orthophosphates (PO43−), indicating higher anthropogenic pressure compared to the Dinaric ecoregion, where water conductivity influenced Chironomidae assemblages. The research has provided valuable and useful information on the chironomid diversity in man-made and highly altered water bodies, as some of the most vulnerable aquatic habitats to anthropogenic influence. The CPET method could be a useful tool for the ecological studies and bioassessment of water quality in Croatia.

Fish diversity in the Nong Leng Sai Wetland, Phayao Province, Northern Thailand, after deep-water dredging

Abstract. Tuncharoen S, Manetam K, Pornpuang S, Chaisan W, Panprommin D, Soonthornprasit K, Pitakpol S. 2024. Fish diversity in the Nong Leng Sai Wetland, Phayao Province, Northern Thailand, after deep-water dredging. Biodiversitas 25: 2738-2746. This study aimed to explore changes in the diversity of fish species in the Nong Leng Sai Wetland, Mae Chai District, Phayao Province, Northern Thailand, after just completed deep-water dredging while shallow-water dredging is in progress. Therefore, three different gill net mesh sizes collected fish specimens from January to July 2022. The results showed that 25 species belong to 23 genera, 13 families from 7 orders, and 21 native and 4 introduced fish species. The fish comprised of the miscellaneous group was the most composed by weight and number, accounting for 45.5% and 52%, respectively, followed by the carp, 38.6% by weight and 45.6% by number. The fish diversity after dredging has decreased, including species and quantity, compared to the diversity reported before. Physical changes in the Nong Leng Sai Wetland resulted from deep water dredging, including increasing water depth, more water storage volume, increased turbidity, and lack of fish shelter and natural food, affecting the diversity of fish species. Furthermore, dredging has stimulated the recovery of aquatic ecosystems regarding water quality, habitat of aquatic animals, and appropriate natural food, which is important for increasing the diversity of fish species and quantities.

Distribution, abundance, and realized niches of meroplankton by two different mesh size nets during spring 2017 in the Southern Yellow Sea, China

Distribution, abundance, and realized niches of meroplankton by two different mesh size nets during spring 2017 in the Southern Yellow Sea, China

Phytoplankton Community Structure in Bun-Bun River Waters, Kubu Raya Regency, West Kalimantan

The Bun-bun River was located in a mangrove forest area in Kubu Raya Regency and empties into the sea. As the main producers at the trophic level of waters, phytoplankton has an important role in assessing river quality. This study aims to find out phytoplankton community structure including abundance, diversity, uniformity, and dominance indexs in relation to Bun-bun River quality. The observations were made in the dry and rainy seasons at three stations starting from the initial end of the mangrove forest (Station 1), the middle (Station 2), and the final end which also empties into the sea (Station 3). Sampling was carried out at three points (left edge, center, right edge). Measurements of physico-chemical factors include brightness, current velocity, temperature, pH, DO, dissolved CO2, salinity, nitrate and phosphate. Phytoplankton sampling used a 30 µm plankton net mesh size and identification down to the species level. The calculated index values include abundance, diversity, uniformity, and dominance. The Bun-bun River was characterized by brackish waters with calm surface currents (<0.1 m.s-1) and a salinity between 5.4-9.48 ppt. Dissolved CO2 levels are relatively high, namely 22-30.8 mg.L-1 in the dry season and 35.2 mg.L-1 in the rainy season. During the dry season, the pH of the water becomes slightly acidic (6.51-6.76) and relatively neutral during the rainy season (7.08-7.52). Nitrate and phosphate levels were low in both seasons and all three stations. The brightness of the water was higher in the dry season than in the rainy season (20-44 cm). A total of 52 types of phytoplankton were found belonging to four classes, namely Class Bacillariophyceae (25 species), Dinophyceae (14), Chlorophyceae (12), and Chrysophyceae (1). Phytoplankton abundance index was low to moderate. The diversity index was moderate at almost all stations except for the low at Station 3 in the rainy season. The uniformity index at Station 3 was low in the dry season but high in the rainy season, and moderate in other locations. The dominance index was high at Station 3 during the dry season and moderate at other locations. Physico-chemical factors such as salinity, dissolved CO2, nitrate and phosphate levels are most likely to influence abundance, while diversity was influenced by dominance.

Trade-off between drag and catch performance when designing zooplankton trawls

The aquaculture sector is in pursuit of sustainable and cost-effective raw materials for feed, and the copepod Calanus finmarchicus is a marine zooplankton species of commercial interest because of its high abundance in northern areas. These copepods have the potential to meet the demand for vast quantities of marine raw materials. However, the lack of an energy- and catch-efficient trawl technology has limited the development of this fishery. Therefore, this study investigated the effect of two central trawl net design parameters mesh size and taper angle to identify which values that provide optimal trade-off balance between gear drag and catch efficiency. We conducted flume tank experiments using a series of plankton nets varying in mesh size (250–1000 μm), solidity ratio (0.54–0.76), and taper angle (5°– 30°) to acquire data on gear drag. The same nets were then used in fishing trials to obtain data on their catch performance. This study shows that zooplankton nets with a mesh size of approximately 500 μm and a low taper angle of about 5° provided the best trade-off between drag and catch performance.

Population dynamics and stock assessment of Queenfish (Scomberoides commersonnianus) from the marine waters of Bangladesh

AbstractThe Queenfish, Scomberoides commersonnianus, is a large commercial fish in Bangladesh. This is the first study on the Queenfish that aims to elucidate life history parameters and stock status to suggest authority for sustainable management and to support future research on this economically significant species in the region. We used three length‐based approaches to establish a standard for sustainable management of the fishery: (1) TropFishR to give the growth parameters and current exploitation status, (2) the length‐based Bayesian biomass estimation (LBB) to quantify stock biomass, (3) and Froese's sustainability indicators (LBI). The length–weight relationship of Queenfish was a negative allometric pattern (b = 2.84; R2 = 0.98). Growth parameters for Queenfish were L∞ = 124.22 cm, K = 0.31 year−1. Instantaneous total mortality Z = 0.71 year−1, instantaneous natural mortality M = 0.36 year−1, and instantaneous fishing mortality F = 0.35 year−1. Based on the LBB approach, the current estimated stock biomass was overexploited (B/BMSY = 0.65). We recommend strictly maintaining mesh size of nets to reduce harvest of immature fish shorter than 62 cm, while focusing harvest on fish 62–74 cm, to minimise recruitment and growth overfishing.

Sea surface microplastics in the Galapagos: Grab samples reveal high concentrations of particles

Plastic pollution in the oceans is increasing, yet most global sea surface data is collected using plankton nets which limits our knowledge of the smaller and more bioaccessible size fraction of microplastics (<5 mm). We sampled the biodiverse coastal waters of the Galapagos Island of San Cristobal, comparing two different microplastic sampling methodologies; 1 l whole seawater grab samples filtered to 1.2 μm and sea surface plankton tows with a net mesh size of 200 μm. Our data reveal high concentrations of microplastics in Galapagos coastal waters surrounding the urban area, averaging 11.5 ± 1.48 particles l−1, with a four-order of magnitude increase in microplastic abundance observed using grab sampling compared with 200 μm plankton nets. This increase was greater when including anthropogenic cellulose particles, averaging 19.8 ± 1.86 particles l−1. Microplastic and anthropogenic cellulose particles smaller than 200 μm comprised 44 % of the particles from grab samples, suggesting previous estimates of microplastic pollution based on plankton nets likely miss and therefore underestimate these smaller particles. The particle characteristics and distribution of these smaller particles points strongly to a local input of cellulosic fibres in addition to the microplastic particles transported longer distances via the Humbolt current found across the surface seawater of the Galapagos. Improving our understanding of particle characteristics and distributions to highlight likely local sources will facilitate the development of local mitigation and management plans to reduce the input and impacts of microplastics to marine species, not just in the Galapagos but globally.

Size at sexual maturity estimation for 36 species captured by bottom and mid-water trawls from the marine habitat of Balochistan and Sindh in the Arabian Sea, Pakistan, using maximum length (Lmax) and logistic (L50) models.

The aim of this study was to estimate the size at first sexual maturity (Lm) for 36 species belonging to 24 families from the marine habitat of Balochistan and Sindh in Arabian Sea, Pakistan through maximum length based an empirical and logistic model using commercial catch during June 2020 to May 2021. Individual total length (TL) was noted up to 0.1 cm using measuring broad. The Lm was calculated using two formulae; (i) log (Lm) = - 0.1246 + 0.9924 * log (Lmax) for Elasmobranchs and (ii) log (Lm) = -0.1189 + 0.9157* log (Lmax) for ray-finned fishes. The minimum Lm was recorded as 10.27 cm TL for Caranx malabaricus and 108.38 cm TL for Isurus oxyrinchus, respectively. Around Lm with 58.33% species were ranges from 19.00 cm to 25.00 cm TL. This study was estimated 16 newly Lm which is globally absent and rest 20 Lm are absent in the Arabian Sea (Pakistan coastal habitats). Therefore, the results will be helpful for the sustainable management and conservation of these marine fishes through the establishment of mesh size of trawl nets based on the size at sexual maturity (Lm).

Seasonal Distribution of Copepods as Influenced by Physicochemical Parameters in Khanki Headworks, Pakistan

Copepods are tiny aquatic animals. Their role in aquatic food chains is very crucial as they are involved in organic matter circulation and energy transfer between different trophic levels. They are important source of food for fish larvae and zooplanktivorous fish. Objective: To assess the influence of environmental variables on the abundance, diversity and seasonal variations of planktonic copepods in Khanki Headworks, Pakistan. Methods: For the analysis of environmental variables monthly water samples from four selected sites were collected for a period of one year (February 2021 to January 2022). Environmental variables were analyzed in laboratory by following standard procedures. Month wise samples of copepods were collected with planktonic net (mesh size: 37µm) from four locations (each with 3 sub-sites). Results: In total, 7 species of Copepods belonging to 4 genera were identified from February 2021 to January 2022. Mesocyclops was observed as the most diverse genus (4 species), while Mesocyclops edax was the most prevalent copepod species. Population density and biodiversity were highest in June and minimum in January. Shannon-Weaver diversity index described greater diversity among copepod species in June. Pearson correlation and canonical correspondence analysis (CCA) revealed that electrical conductivity (EC), temperature, turbidity, pH and dissolved oxygen (DO) were important environmental variables affecting the biodiversity and density of copepods. Conclusions: This investigation elucidated that physicochemical parameters generally regulate the population dynamics of Copepods.

Population Dynamics of Copepods as Influenced by Heavy Metals in Khanki Headworks, Pakistan

Copepods grow in diverse freshwater habitats, totaling around 2,814 species. As foremost zooplankton, they lead biomass and are pivotal in aquatic ecosystems. The ever-increasing issue of heavy metals contamination affects organisms differently. Copepods, with their broad geographic range, can be valuable bio monitors for metal growth. Objective: To evaluate the effects of heavy metals and fish diversity on the population dynamics of copepods in Khanki Headworks, Pakistan. Methods: For the analysis of heavy metals month wise water samples (1000 ml) from four selected sites were collected for one year (February 2021 to January 2022). Atomic Absorption Spectrophotometry was employed for the analysis of heavy metals. Month wise copepods samples were collected with planktonic net (mesh size: 37µm). Results: In total, seven species and four genera of copepods were identified. Mesocyclops edax was the most dominant copepod species. Three heavy metals zinc (Zn), arsenic (As) and nickel (Ni) were estimated in following order of concentrations Zn&gt; Ni&gt; As. Conclusions: Current investigation revealed that heavy metals generally govern the population dynamics of copepods.

Seasonal Variations in Ostracod Community Structure and Physicochemical Parameters in Khanki Headworks, Pakistan

Protozoans, rotifers, ostracods and copepods are principal groups of zooplanktons. These organisms are crucial biotic elements, and impact all functional features of aquatic ecosystems. Objective: To assess the impacts of environmental variables on the abundance, biodiversity and seasonal distribution of ostracods in Khanki Headworks, Pakistan. To evaluate the contribution of ostracods as bio-monitors of contamination in freshwater ecosystems. Methods: Month wise separate water samples were taken for different environmental variables from four sampling sites (each with 3 sub-sites), for study period of one year (February 2021 to January 2022), whereas, samples of microcrustaceans (ostracods) were collected with planktonic net (mesh size: 37µm). Results: In total, 5 species of ostracods, associated to 4 genera and 2 families were identified from February 2021 to January 2022. Heterocypris incongruence was the most abundant species, whereas, Dolerocypris sinensis was noted as least abundant species. Ostracods abundance and biodiversity were monitored highest in June and minimum in the month of January. Results of Pearson correlation showed that physicochemical parameters, electrical conductivity (EC), temperature, turbidity, total dissolved solids (TDS) and pH have positive effects on the density and diversity of ostracods. In contrast, dissolved oxygen (DO) showed negative relationship with the abundance and diversity of planktonic ostracods. These findings were further validated by Canonical correspondence analysis (CCA). Conclusions: This investigation revealed that physicochemical parameters generally govern the population dynamics of ostracods.

Assessment of motorized commercial gillnet fishery of the three commercially important fishes in Lake Tana, Ethiopia

This study was conducted from July 2010 to June 2011 to assess the status of motorized commercial gillnet fishery of the three commercially most important fishes in Lake TanaLabeobarbusspp., Oreochromisniloticus(Nile tilapia) and Clariasgariepinus (African catfish). Catches were monitored daily and additional information on number of gillnets used, mesh size of gill nets and location of fishing grounds were collected. Data on the Labeobarbus species composition were collected 3 days per month. The total fish yield from the main fishing grounds of the commercial fishery was 238 metric tons/year. The catch of tilapia was 71%, that of catfish 18% and that of Labeobarbus 11% of the total catch. Peak production was from March - May 2011. Most effort (80%) was allocated to the North Eastern Floodplain (NEFP). The total number of gillnets set and boat trips made were 85,943 and 3104, respectively, which is much higher than reported previously. Consequently, the Catch per Unit effort (CpUE; kg/trip) of the 2010/2011 production year was with 64.7 ± 3 (95% CL) kg much lower than reported previously. The CpUE of all three fish taxa was lower than previously reported, but especially the LabeobarbusCpUE was much lower than before (6.1 kg). An integrated management plan and research program for the Lake Tana basin is urgently required to prevent the collapse of an important fishery and the extinction of the only known cyprinid species flock in the world.

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

The Temengor Reservoir is the second largest reservoir in Peninsular Malaysia. Located in the northwestern state of Perak, it was selected to develop a large-scale tilapia (Oreochromis niloticus) aquaculture facility within the Aquaculture Industrial Zone (AIZ) in 2008 due to its favourable environmental conditions. No record of tilapia has ever been reported in the natural waters prior to this. However, a post-establishment study recorded tilapia sightings in the natural waters of this lake. The cultured tilapia was easily recognizable with the elongated mouth and body, and long caudal fin. It is postulated that these were escapees from the floating cages that had invaded the natural waters and would negatively impact the native fish species. To test our hypothesis, we investigated the impact of the aquaculture facility on native fish diversity through a spatial design. The study was focused on assessing the impact of tilapia culture at sites nearer to the AIZ vs more distant sites, the former with a greater likelihood of receiving escapees. Two major sites were chosen; within 5 km (near-cage) and within 5-15 km (far-cage) radii from the AIZ. Fish sampling was conducted using multiple mesh sizes of gill nets (3.7, 5.1, 6.5, 7.6, and 10.2 cm) deployed at the littoral zone of the sampling points. Species diversity, abundance, dietary habits, and habitat preference were investigated. The CPUE (individual/hour) of native fish species at the far-cage site of the AIZ Reservoir was found to be significantly higher (p < 0.05) than that at the near-cage site. Principal component analysis (PCA) based on diet and habitat preferences showed that the tilapia, O. niloticus had almost overlapping diet resources and habitat with native fish species. We conclude that there is a correlation between the reduced catches of native species (based on CPUE) and the high presence of tilapia. Thus, appropriate actions must be implemented for strategic and effective planning in terms of native fish conservation.

Before and after closed season for beach seine fishing in Ghana: Impact on benthic macroinvertebrates species diversity indices

AbstractBeach seine fishery provides a means of livelihood to many households in Africa and it is widely practiced in the coastal communities of Ghana due to the relatively cheaper operational cost. However, the small mesh sizes of beach seine nets and fishing activities that involve dragging a net through the nearshore seabed tend to destroy fish breeding grounds and capture juvenile fish and non‐target benthic macroinvertebrates, which get discarded. This study investigated the impact that before and after closed season for beach seine fishing had on macroinvertebrates species diversity indices at two Ghanaian beaches with different fishing pressures. The study was carried out at OLA and Sisimbo Beaches located in the Central Region of Ghana, taking advantage of the statutory 1‐month national fishing closed season in July 2022. Six (6) replicate sediment samples were taken at each beach after landing by beach seine fishers every month for 6 months, from April to June, and August to October, representing before and after closed season, respectively. Benthic macroinvertebrates were retrieved from the samples using appropriate protocols and subjected to indirect (Shannon, Simpson, Rényi) and direct (species abundance models, species accumulation models, multivariate statistics) measures of species diversity analyses. The indirect species diversity indices increased monotonically the following 2 months after closed season but reduced in the third month after closed season at both beaches. Conversely, the direct measures of diversity indices revealed that closed season for beach seine fishing improved species numbers and richness at both study beaches. This is the first report on the impact of a closed season on macroinvertebrates in any African country.

Growth patterns and reproductive aspect of Naleh (Barbonymus sp.) in Krueng Lanca, Nagan Raya Regency, Aceh Province

Naleh (Barbonymus sp.) is one species of native fish found in Aceh Waters. This study examines the growth patterns and reproductive aspects of the fish in Krueng Lanca of Nagan Raya, Aceh Province. The study lasted five months (January - May 2022). Sampling was carried out purposively, once a month, on five different stations using gill nets (mesh size: 0.5 inches, 1.0 inches, and 1.5 inches and cast nets (D: 6 meters, mesh size: 0.5 inches). A total of 171 Naleh was caught in these waters. The calculation results obtained a length-weight relationship W = 0,0003*L2.2234 (r2 = 0.8823) for males, which shows the nature of allometric and W = 6E-06*L3.0684 (r2 = 0.8566) for females which shows the isometric. The sex ratio of Naleh in these waters was 1.1: 1. The size of the first mature gonads was 60-69 mm (males) and 90-99 mm (females) with a Gonadosomatic Index of 1.92-3.04 % (Males) and 8.73-11.61 % (females). The peak of the Naleh spawning season in Krueng Lanca waters was thought to occur from March to April, with the number of eggs ranging from 1,853-3,813 and a diameter of 1.18-1.43 mm. Based on the oocyte distribution, the peak of spawning of the fish was categorized as multiple spawners.

Synchaeta’s community in the urban coastal area of the Thessaloniki Bay

Rotifers’ presence and significance are being underestimated among marine zooplankton because rotifers are lost when using larger mesh size nets. Furthermore, samples’ preservation often makes species identification difficult, creating a knowledge gap regarding their diversity and abundance in coastal ecosystems. Our study aimed to address this gap by documenting the biodiversity and distribution patterns of the rotifer species, exploring their relationships with the components of the zooplankton community and determining the environmental variables driving their seasonal dynamics. Samplings were carried out in an urban coastal area in the North Aegean Sea in Greece, within two sampling periods. Four coexisting Synchaeta species were encountered, whose temporal distribution patterns were mainly driven by temperature; S. neapolitana exhibited a preference for colder temperatures, contrary to the thermophilic distribution patterns of S. baltica and S. vorax. Network analysis unveiled several negative links among Synchaeta species and other zooplankton taxa, suggesting potential competitive trophic interactions. The present study is one of the very few dealing with marine rotifers across the Mediterranean Sea and thus provides a significant contribution to our understanding of the dynamics of this group of micrometazoans.

Analisis Keragaman Fitoplankton di Sungai Barumun Kecamatan Panai Tengah Kabupaten Labuhanbatu

Research on the analysis of the diversity of phytoplankton has been carried out in the Barumun River, Panai Tengah District, Labuhanbatu Regency. The Barumun River is widely used by the surrounding community for various activities, for example: disposal of industrial waste, household waste, fish auctions, ports, and fishing. This activity resulted in the Barumun River being polluted with increasingly turbid water color. The purpose of this study was to determine the diversity of phytoplankton in the Barumun River. This type of research is a descriptive research with a quantitative approach. Sampling used Plankton Net mesh size 30 μm from 3 stations with 10 repetition, observed using a microscope, identified using the book "Marine and Fresh Plankton", counted, and analyzed the diversity index of plankton in the Zoology Laboratory, Biology Education Department, FKIP, University Labuhanbatu. Plankton abundance was calculated using the Lackey Drop micro-count method and Plankton diversity was calculated using the Shannon-Wiener formula. The results showed that the phytoplankton found were dominated by Diatoms and Dinoflagellates, with the highest average abundance being from the genus Cerratulina (1015 ind/L), and the lowest abundance value was from the Protoperidiun genus (5 ind/L). The diversity index is included in the moderate diversity category (1.48-1.90), and the dominance index is in the range of 0.24-0.28 with a low category.

The Composition of The Catch in The Danish Seine Operating in The Java Sea

Fishing gear with a good level of environmental friendliness will be selective in fishing, by choosing the right location and using net mesh sizes that can select the fish to be caught. For this reason, this study was carried out to analyze the composition of the catch from the Pocket Drag Net. The types of fish caught in percentage are as follows: swanggi fish (Priacanthus tayenus) at 29.9%; etong fish (Abalistes stellaris) by 11.2%; mackerel (Scomberomorus commerson) by 0.14%; tiger grouper (Epinephelus fuscoguttatus) by 1.5%; yellowtail fish (Caesio teres) by 1.7%; red snapper (Lutjanus sp.) by 0.7%; Stingray (Dasiatis zugei) at 1.5%; Kurisi fish (Nemipterus japonicus) amounted to 22.2%; Ray shark (Rhynchobatus australiae) by 1.15%; Brown (Scolopsis taeniopterus) by 21.2%; and Manyung (Netuma thalassina) at 7.9%. Based on the percentage composition of the catch, Swanggi fish is the highest main catch fish with a percentage of 29.9% and the lowest main catch fish is red snapper, namely 0.7%. Meanwhile, by-catch fish such as mackerel were also caught with a percentage of 0.14%.