Length-weight relationship of 12 species of freshwater fish caught in the middle and lower stretches of the Negro River basin,Brazilian Amazon

This study aimed to estimate the parameters of the length-weight relationship for 12 freshwater fish species that inhabit lakes in the Negro River basin (Amazonas state, Brazil). The fishes were sampled using gillnets (15 × 2 m, mesh size 30–100 mm between knots), during the hydrologic cycle: low water (dry), flooding, high water (flood), and receding water, from 2008 to 2010, 2012 and 2013. The gillnets were placed in the lakes with a standardized period of 24 hr, with fish removal occurring every 12 hr (2010 to 2010) and 6 hr (2012 and 2013). Measurements were taken for standard length (SL – 0.1 cm precision) and total weight (TW – 0.1 g precision). The parameters a and b of the equation WT = a.LT^b were estimated. This study also provides new data on of maximum lengths for three species.     

Length-weight relationship of 16 fish species from the Negro River basin (Amazonas state,Brazil)

This study aimed to estimate the parameters of length-weight relationship for 16 freshwater fish species that inhabit the Aracá and Demeni Rivers, which are two tributaries of the Negro River (Amazonas state, Brazil). The fishes were sampled using gillnets (15 × 2 m, mesh size 30–120 mm between opposite knots), during 6 days each year, in April 2016, November 2018 and April 2019. The gillnets were placed in the river twice each day; in the morning (5–9 a.m.) and in the evening (5–9 p.m.), with a standardized time of 4 hr. Measurements were taken for standard length (SL – 0.1 cm precision) and total weight (TW – 0.01 g precision). The parameters a and b of the equation W_T = a.L_T^b were estimated. This study also provides new data on of maximum lengths for six species, namely, Argonectes longiceps, Hemiodus atranalis, Chalceus erythrurus, Astrodoras asterifrons, Trachydoras steindachneri and Acarichthys heckelii.     

Length-weight relationship of fish species from Central Amazon floodplain

Length-weight relationship (LWR) for 39 freshwater fish species captured in the Catalão Lake, a floodplain area at the confluence of the Amazonas and Negro rivers is presented. LWRs were calculated based on fish sampled over 18 years (1999–2017) using a set of ten gill nets with different mesh sizes, monthly immersed in water for 24-hr with 6-hr interval catches. Measurements were done for standard length (SL – 0.1 cm precision) and total weight (TW – 0.01 g precision). The LWRs were calculated by the linear regression of natural log-transformed SL and TW data: TW = a × SL^b. All statistical analyses were performed with R software. From all species considered, 32 are new LWR records for the international literature as well as for the Amazonian ichythyofauna; additional records expand the known size range for seven species.     

Length-weight relationships of five fish species from Brazilian Amazon coast hotspot estuaries

The length-weight relationships (LWR) were estimated for five fish species from the Golfão Maranhense, Brazilian Amazon littoral region. Samplings were performed in August 2016, during the dry season, using trawl net with 6.0 m length by 3.0 m width (trawl mouth opening of 6.0 m²) and 1.0 cm mesh size between opposite knots. This study registers LWR for Anchoviella elongata and Gobioides broussonnetii and the estimated LWR for Aspredo aspredo and Aspredinichthys filamentosus covers a wider size range. Moreover, it is presented maximum length values for A. elongata and Sphoeroides greeleyi.     

Length-weight relationships of fish species from oxbow lakes on the floodplain of the middle Purus River in western Brazilian Amazon

The length-weight relationship (LWRs) was estimated for eight fish species collected from oxbow lakes on the floodplain of the middle Purus River in western Brazilian Amazonia in January, May, and September 2012. The specimens were collected using 12 gillnets (80 m in length × 4 m in height, meshes of between 1.5 cm and 12.0 cm), which were set during both diurnal and nocturnal periods. The species had allometric coefficients (b) of between 2.92 and 3.37, and correlation coefficients (r²) ranging from 0.954 to 0.993 and we highlight that the work presents new data for literature.     

Length–weight relationships of four freshwater ornamental fish species from the Brazilian Negro River basin

The present work reports the length–weight relationships (LWR) for four ornamental fish species from the middle Negro River basin, Amazonas, Brazil. The r² value ranged from 0.810 to 0.941 and values of b varied from 2.346 to 3.442. These results represent the first reference on LWR for all four species, based on FishBase.     

Length-weight relationships of six fish species from the Xiangjiang River in Guangxi region,China

This study aimed to estimate the parameters of length-weight relationships (LWRs) for six freshwater fish species that inhabit in the Xiangjiang River of Guangxi region, China. The specimens were sampled in April, July, and October 2014 and in January 2015 using electrofishing (CWB-2000P, China; 12 V import, 250 V export) and traps (mesh size 8.5 mm; length 200 m) at five sampling sites. For each sampling site, a trap was settled on one nearshore zone of the river for 24 hr, and the electrofishing was applied within 30 min from downstream to upstream with 200 m long. Standard length was measured (be accurate to 0.1 cm) and total weight determined (be accurate to 0.1 g) after preservation in formaldehyde (10%). The values for the parameter b of the length-weight relationships were estimated together with the coefficient of determination scores. In addition, this study provides a new tentative LWRs for the six species.     

Length-weight relationships of fish species from the Stung Russei Chrum River basin,Kingdom of Cambodia

This study evaluated the length-weight relationships (LWRs) for three teleost fish species sampled from the Stung Russei Chrum River basin, Kingdom of Cambodia. The fish were collected during two dry seasons (April 2019 and November 2019) and one rainy season (October 2018) using monofilament trammel nets (2–12 cm mesh size), cast net (mesh size 2 cm) and scoop-nets (mesh size with 0.3 cm). Results showed that all fitted regressions were highly significant and the coefficients of determination (r²) were high. This study expanded the value of maximum total length for Cyclocheilichthys apogon and Poropuntius laoensis while reported the wider ranges of total mass for Poropuntius laoensis. Moreover, our present study also provided the novel LWRs records for Hemibagrus filamemtus.     

Length-weight relationship of 13 middle Uruguay River basin species,Southern Brazil

Length-weight relationship (LWRs) were determined for 13 fish species from the Uruguay River. The fish were caught in six locations and sampled at each location during each season, totaling 72 samplings, starting in May 2016 and ending in February 2018. Various materials were used such as gillnets (15; 20; 25 30; 40 and 80 mm, triple mesh 150.30.150 150.40.150 and 150.50.150 mm, 8 mm trawl). We also used two longlines, 100 m long, 30 hooks each (hooks 5/0 and 12/0), baited with small fish, corn and snail. Length-weight relationship were adjusted appropriately for all species (r² > .95). The b values of the LRW equations ranged from 2.38 in Steindachnerina brevipinna to 3.62 in Pimelodus atrobrunneus.     

Length-weight relationship of six coastal fish species from Gulf of Mannar,South-east coast of India

The parameters ‘a’ and ‘b’ of length weight relationship of 6 species (Scolopsis vosmeri (Bloch, 1792), Engyprosopon macrolepis (Regan, 1908), Bleekeria murtii Joshi, Zacharia&Kanthan, 2012), Centriscus scutatus Linnaeus, 1758, Samaris cristatus Gray, 1831 and Iniistius bimaculatus Ruppell, 1829) are reported from the Gulf of Mannar, South east coast of India. The fish samples were collected from experimental trawling conducted twice a month during the period August to December 2012 and September to December 2013 at a depth ranging from 8.5 to 20.5 m. Three hauls were made in a day with each haul of one hour duration. The total length of the gear was 32 m with a cod end mesh size of 30 mm. The total length of the fish was measured to the nearest 0.1 cm and weight to the nearest 0.1 g.     

Length-weight relationships of four fish species from the Yalong River,China

Parameters of the length-weight relationship (LWR) were estimated for four fish species [Beaufortia szechuanensis (Fang, 1930), Claea dabryi (Sauvage, 1874), Percocypris pingi (Tchang, 1930), and Yunnanilus sichuanensis Ding, 1995] from the Yalong River. Samples were collected seasonally from June 2018 to July 2019, using various fishing gears [set nets (mesh: 1.5 × 2.0 cm), hook, drift gill nets (three mesh sizes: 1.0; 2.0; 3.0 cm) and electro fishing]. Two new maximum standard length were recorded for C. dabryi and P. pingi.     

Length-weight relationships of four fish species from the Hei River in northwest China

Length-weight relationships (LWRs) were assessed from four fish species in Hei River in northwest China. All specimens were collected using (fishing1 km along the river and 3 meters along the river bank) and netting (gill nets, nets: 30 × 1.2 m; mesh size: 3 × 3 cm) and shrimp cages (nets: 20.0 × 0.5 × 0.4m; mesh size: 0.5 cm) seasonally from April 2019 to October 2020. The gill nets and shrimp cages were soaked in water in the afternoon and pulled in around 10 a.m. the next day after an overnight stay. These specimens were measured for total length (L, 0.1 cm) and body weight (W, 0.1 g) while the specimens were fresh. The parameters for the LWRs were estimated with the basic statistical analyses. The study provided the new maximum total length for Gymnocypris chilianensis (21.0 cm) and Triplophysa tenuis (17.0 cm).     

Length-weight relationships of six tropical estuarine fish species from Pulicat lagoon,India

Length–weight relationships (LWRs) of six finfish species under two families of the order Perciformes collected from Pulicat lagoon (India) are presented in this study. The fish specimens were collected weekly from the catches of shore seine net (with a mesh size of 50mm at the main webbing and 10 mm at the cod end) operated in the lagoon at an average depth of 2.5 m by the local fishermen during the period from July 2018 to April 2019. This study reports the LWRs for five gobiid and one siganid fish species which have no earlier reports on LWRs. The calculated ‘b’ value ranged from 3.538 (Favonigobius reichei) to 2.677 (Oxyurichthys microlepis) and ‘a’ value varied from 0.0041 (Favonigobius reichei) to 0.0199 (Acentrogobius cyanomos). This study also reports the new maximum total length (TL_max) for the gobiid fish species Oxyurichthys microlepis.     

Length-weight relationships of eleven fish species captured in 18 streams of the Capim River basin,Brazil

The length-weight relationship is important for the study of populational dynamics. This study aimed to describe the length-weight relationships (LWR) of 11 fish species sampled on 18 streams of the Capim river basin on eastern Amazon. Specimens were captured in 2014, 2015 and 2017, using sieve nets with 2 mm of mesh size. Fixed specimens were fixed in 10% formalin and conserved in alcohol 70%, measured for standard length (SL, 0.1 cm) and total weight (W, 0.01 g). The 11 species analysed were: Hemigrammus bellottii, Hemigrammus ocellifer, Hyphessobrycon heterorhabdus, Iguanodectes rachovii, Copella arnoldi, Nannostomus trifasciatus, Apistogramma regani, Apistogramma agassizii, Gymnorhamphichthys rondoni, Hypopygus lepturus, Anablepsoides urophthalmus.     

Length-weight relationships of six fish species of tropical lake,Mexico

The length–weight relationships (LWRs) for six native fish species from the Chapala Lake, Mexico, are described in this paper. The fish were caught monthly with the support of local fishermen from different landing sites. The daily catch is obtained using the nasa charalera (pot) and the gill net. Each fisherman can operate 20 pots daily at each fishing site for approximately six or seven months; this pot is a 2 m long cylinder, 0.5 m in diameter, with a mesh opening of 0.5 to 1 cm. Also, each fisherman can set between 10 and 20 gill nets each day at sunset and recover them in the morning, again for six or seven months. The length of the gill net is 30 m or more with a 2 m drop, with a 1 cm mesh size. The study provides basic data, morphometric data on length and weight of native species belonging to the genus Chirostoma. These species are of great importance for the local fishery with the Mesa Central of Mexico.     

Length-weight relationship of six demersal fish species from Gulf of Mannar,Bay of Bengal,Eastern Indian Ocean

Length-weight relationship (LWR) parameters were analysed for six demersal finfish species from the Gulf of Mannar coast, Bay of Bengal. Fishes were sampled monthly from the landings of trawlers operated along the coast of Tuticorin and Rameshwaram with a cod-end mesh size of 35 mm at the depth of 60–80 m. Fish specimens were sampled by measuring the total length (TL) and total weight (TW) with precision to 0.1 cm and 0.1 g respectively. The present study also recorded a new maximum total length for Engyprosopon macrolepis, Torquigener brevipinnis and Leiognathus brevirostris.     

Eunotia amazonica sp. nov. (Bacillariophyta), a common stalk-forming species from the Rio Negro basin (Brazilian Amazon)

A new stalk-forming diatom was observed at high relative abundances on periphytic samples collected in the Rio Negro hydrographic basin (Brazilian Amazon) and is here described using light and scanning electron microscopy. We also present ecological preferences of the new species. Eunotia amazonica sp. nov. co-dominated periphytic samples collected during the rainy seasons of 2013 and 2014 near the city of Manaus (Amazonas, Brazil). The main diagnostic feature of the new species is the stalk-forming growth form (‘Cymbella-like’) illustrated here for the first time in the genus Eunotia Ehrenberg. Previous reports on growth forms in common European databases for this genus included colonial (‘ribbon-like’) but also ‘mobile’, ‘fixed by pads’ or ‘without structures of fixation’. We demonstrated that the three dominant Eunotia species in periphytic samples from the Rio Negro all exhibited distinct ‘growth forms’ or habits: Eunotia amazonica sp. nov. (stalked), Eunotia intricans Metzeltin & Lange-Bertalot (ribbon-like) and Eunotia rabenhorstiana (Grunow) Hustedt (branched-arborescent). The high diversity of species, many of which are unknown to science, as well as the poorly known life-forms and habits of the Eunotiaceae in the region, partially prevent the use of metrics based on life-form to assess ecological changes. Generic assumptions based on robust statistical methods may obscure reality and lead to biased conclusions of diatom community changes in poorly explored regions such as Neotropical freshwater rivers, where the Eunotiaceae are largely dominant, particularly in the Amazon basin.     

Length-weight relationships of 37 freshwater fish species from the Lefini river,middle Congo River basin (Republic of the Congo)

The present study reports on length-weight relationships (LWRs) for 37 of the most abundant fish species in the Lefini River basin, one of the largest right bank tributaries of the Congo River in the Republic of the Congo. The study area comprised 12 stations along 103 km of the river. Each station was sampled during March 2007 to August 2008 following standardized methods utilizing five monofilament gill nets of 10, 12, 15, 20 and 30 mm mesh size. Sample size, lengths, weights, LWRs, 95% confidence intervals of a and b, coefficient of correlation r² and growth type are provided for each species. Values of allometric coefficient b of the LWRs (W = aSL^b) ranged from 2.556 for Synodontis nigriventris to 3.363 for Brycinus poptae. These results represent the first study of length-weight relationships for fish species in a large affluent of the Congo basin as a whole.     

Length-weight relationship of 74 fish species caught in the continental coast of Ecuador

This work analysis the length-weight relationships for fish species captured by artisanal fishery along the continental coast of Ecuador. Fishermen used the following fishing gear: beach seine nets (5.1–31.8 mm), shrimp trawl nets (21.8–31.8 mm) and bottom gill nets (54.1–203.2 mm). Sampling took place during the years 2012 and 2014. Frequency of sampling was monthly, and it was completed systematically from Southern toward Northern Provinces. Length-weight relationship (LWR) was realized by the power model (y = a × x^b), for species with a bivariate dataset >70. A total of 59 commercial and 15 non-commercial species were registered. For 74 species, our analysis including a higher total length not reported in LWR estimates previously. The determination coefficient (r²) value was always above 0.95.     

Length-weight and length-length relationships of three fish species from the lower Yalong River,China

Length-weight relationships (LWRs) and length-length relationships (LLRs) were evaluated for three endemic fish species sampled from the lower Yalong River and its biggest tributary (the Anning River), in China. Specimens were captured using set gillnet (mesh size 4 cm) and backpack electro-fishing (power output 400 W, depth fished 1 m, area covered 3 m²) from June to July 2018. LWRs and LLRs are presented for the following species (Sinogastromyzon sichangensis, Micropercops swinhonis and Percocypris pingi).