Nets Of Different Sizes Research Articles

Spatial and temporal variation of ichthyo-faunal diversity with relation to environmental variables in the Lohandra River of eastern, Nepal

The present study aimed to examine space and time variation in fish community structure with relation to environmental variables in the Lohandra River. Fish samples were collected based on different habitat representations from March 2020 to February 2021, covering 12 months. Fish sampling took place from 6 am to 9 am. For the fish sampling, two cast nets of different sizes were used, one having a large mesh size of having a mesh size of 1 cm, 5 m diameter, and 5 kg weight and another having 0.5 cm, 3 m diameter, and 2 kg weight, covering 200 to 250m across each station to cover all possible areas. In addition, monofilament gill nets with mesh sizes of 6, 8, and 10 cm were used to capture the fish. In each station, 9-gill nets were left late in the evening (5 pm – 6 pm) and taken out early in the morning (6 am – 7 am) in a sampling distance of 200 - 250m. A total of 1178 specimens representing 72 species belonging to 10 orders and 25 families were documented. An analysis of similarity (ANOSIM) testing for both time (R=-0.25, P>0.05) and space (R=-0.28, P>0.05) showed no significant dissimilarity in fish assemblage structure. Results from the similarity percentage analysis (SIMPER) indicated that the fish species: Cirrhinus reba, Labeo bata, Cirrhinus mrigala, Labeo boga, Puntius sophore, Salmostoma bacaila, Channa orientalis, Chagunius chagunio, Glossogobius giuris, Labeo caeruleus, Barilius bendelisis, Colisa faciatus, Esomus danricus, Salmostoma acinaces, and Chitala chitala. The CCA revealed that of the selected environmental variables, three parameters namely, transparency, water temperature, and water velocity (p<0.05) were found to be influencing factors to determine the fish assemblage structure of the Lohandra River.

The Influence of Contracaecum larvae (Nematoda, Anisakidae) Parasitism on the Population of Prussian carp (Carassius gibelio) in Lake Sakadaš, Croatia.

Contracaecum larvae are geographically widely distributed, utilizing many animal species as hosts; and fish represent an important paratenic host in their life cycle. Their presence in Prussian carp (Carassius gibelio) was studied in Lake Sakadaš (Croatia) in 2017 and 2018. Two gill nets of different sizes submerged during a 12-h period were used to collect the fish. Contracaecum larvae were recorded in the stomach, slightly coiled or elongated on the intestine serosa or encapsulated in a gut wall of 20 individuals. The effect of Contracaecum sp. on the health of their host was determined by estimating the effect of the parasites’ presence, number, and biomass on fish length, weight, and the Fulton’s condition factor (CF). Infected fish showed negative (b < 3; p < 0.05) and uninfected fish positive allometric growth (b > 3; p < 0.05). Fish weight and CF in infected individuals were significantly low in comparison to the uninfected ones (Mann–Whitney U test: U = 1078.00, U = 423.50, respectively; p < 0.004). These results emphasize the importance of evaluating parasitic nematode presence in economically important fish species. Even more, if this endoparasite has a detectable negative impact on a resilient species such as the Prussian carp, it is important to monitor its occurrence in other fish species.

Ichthyofaunal diversity with relation to environmental variables in the snow-fed Tamor River of eastern Nepal

Tamor River in eastern Nepal supports diverse hill stream fishes. From winter, spring, summer, and autumn of 2020, we investigated the ichthyofaunal diversity with environmental variables in the snow-fed Tamor River covering four seasons (winter, spring, summer, and autumn) and field surveys were carried out in January, April, July, and October 2020. We used two cast nets of different sizes, one with a mesh size of 2 cm, 6 m diameter and 6 kg weight and another having 0.5 cm, 3 m diameter and 2 kg weight. In addition, monofilament gill nets with mesh sizes of 6, 8, and 10 were used for fish sampling. A total of 6,373 fish individuals representing 28 species belonging to three orders, seven families, and 16 genera were recorded. One-way permutational multivariate analysis of variance (perMANOVA) on the Non-metric Multidimensional Scaling (NMDS) showed no significant (P &gt;0.05) difference between winter, spring, and autumn season but summer season showed significant (P &lt;0.05) difference from winter, spring, and autumn seasons. Furthermore, one-way analysis of variance on redundancy analysis (RDA) vindicated that among the selected parameters, pH, air temperature and total hardness were the influencing factors (P &lt;0.05) to determine the fish community structure in Tamor River.

Fish Diversity and Water Quality Parameters of Mechi River, Jhapa, Province No. 1, Nepal

Species diversity is widely recognised as an important trait of functioning and resilient ecosystem. Spatio-temporal patterns of fish community structure in the Mechi River was studied based on stratified random survey, conducted between September 2018 and April 2019. The survey was conducted at three different sampling stations in three different seasons. For the fish sampling, two cast nets of different sizes were used, one having large mesh size of 0.5 cm, 3 m diameter and 2 kg weight and another having mesh size of 2 cm, 6 m diameter and 6 kg weight. In addition, drag net and gill net were also used to collect the fish samples. A total of 1,772 fishes belonging to 4 orders, 8 families, 16 genera and 33 species were documented. The results from the similarity percentage analysis indicated that, the species Schistura devdevi, Brachydanio rerio, Puntius sophore, Barilius barila, Schistura beveani and Puntius terio were the most copious fish species recorded from the Mechi River. One-way analysis of similarity testing for space and time variations in fish community indicated that there was a significant difference in space (R = 0.66, p&lt;0.01) but no significant difference in time (R = -0.0123, p&gt;0.433). The Canonical Correspondence Analysis hinted that dissolved oxygen, water velocity and pH have shown to influence the fish assemblage structure in Mechi River.

Trophic ecology of two piranha species, Pygocentrus nattereri and Serrasalmus marginatus (Characiformes, Characidae), in the floodplain of the Negro River, Pantanal

AIM: This study aimed to evaluate influence of hydrological variation, ontogeny and interspecific variation in the feeding activity and diet composition for P. nattereri and S. marginatus in floodplain of Negro River, South Pantanal. METHODS: The samples were taken with the use of gillnets and cast nets of different sizes, from October/2005 to August/2008. RESULTS: We sampled 748 specimens, 442 of P. nattereri and 306 of S. marginatus. We identified 31 items in the dry and 14 in the flood season for P. nattereri, and 29 items in the dry and eight in the flood season for S. marginatus. For both species, fish was the predominant food item in both seasons. The PERMANOVA results showed that the diet varied significantly between the two species (p&lt;0.001), during ontogenetic development (p&lt;0.001) and seasonally (p=0.024). The ancova results suggests that the intensity of food intake was higher in the dry season (p&lt;0.001) for both species. The niche breadth varied only between studied species with S. marginatus presenting higher niche breadth than P. nattereri. CONCLUSION: Piranhas feed more during dry season, probably because in this period food is more varied and abundant, due to the concentration of fish in the main river channel. There were ontogenetic changes in the diet, with no feeding overlap between the two species, probably because of differences in preference for some items and differences in feeding behavior displayed during hunting attacks.

Species Richness and Invasion Vectors: Sampling Techniques and Biases

During a European Union Concerted Action study on species introductions, an intercalibration workshop on ship ballast water sampling techniques considered various phytoplankton and zooplankton sampling methods. For the first time, all the techniques presently in use worldwide were compared using a plankton tower as a model ballast tank spiked with the brine shrimp and oyster larvae while phytoplankton samples were taken simultaneously in the field (Helgoland Harbour, Germany). Three cone-shaped and 11 non-cone shaped plankton nets of different sizes and designs were employed. Net lengths varied from 50 to 300 cm, diameters 9.7–50 cm, and mesh sizes 10–100 μm. Three pumps, a Ruttner sampler, and a bucket previously used in ballast water sampling studies were also compared. This first assessment indicates that for sampling ballast water a wide range of techniques may be needed. Each method showed different results in efficiency and it is unlikely that any of the methods will sample all taxa. Although several methods proved to be valid elements of a hypothetical `tool box' of effective ship sampling techniques. The Ruttner water sampler and the pump P30 provide suitable means for the quantitative phytoplankton sampling, whereas other pumps prevailed during the qualitative trial. Pump P15 and cone-shaped nets were the best methods used for quantitative zooplankton sampling. It is recommended that a further exercise involving a wider range of taxa be examined in a larger series of mesocosms in conjunction with promising treatment measures for managing ballast water.

Slowness vector correction for teleseismic events with artificial neural networks

The slowness anomalies cause serious location errors. The objective of this study is to create a mapping from observed slowness values to corrected values, which will provide more accurate locations. Artificial neural networks (ANNs) are efficient tools for mapping one multidimensional space to another. ANNs have been applied to compute slowness vector corrections for teleseismic events. Separate databases were used for training, testing and validating the networks. The training data set consisted of 2218 events in the period 1988–1992. An independent test database consisted of 1091 events from the year 1993 and the first half of 1994. The observed slowness vectors were computed using a three-station array of short period stations, KEF, SUF and KAF, in central Finland. The type of neural network was multi-layer perceptron. To improve the learning capability of the networks, a set of region-dependent extra inputs, resembling bias inputs, were added to the input layer. Several nets of different sizes were tested. The smallest net with only two hidden nodes gave best results. The median of error of the validation database dropped from 523 to 138 km. The median of error after correction is smaller than achieved with the method previously used with these stations. Due to the good interpolation capability of the neural net, the corrections decreased the location error even on areas which had no previous events in the training database. The method can be applied to slowness vector correction at any type of station or array, which produces slowness and azimuth values, if the mapping from the observed slowness values to calculated values is unambiguous.