Length-weight relationship of six small fish species from the Negro River basin in the Brazilian Amazon

The main objective of the study was to estimate the parameters of the length-weight relationship for six small fish species of lower Negro River basin. The fish were sampled using monofilament gillnets (20 × 2 m, mesh size 5 mm between knots), and landing net for 2 days of each month in September and December 2017 and February, March and April 2018. The gillnets were placed in the river twice a day, in the morning (9–11 a.m.) and the afternoon (3–5 p.m.). Total length and total weight were measured to a precision of 0.1 cm and 0.01 g, respectively. The parameters a and b of the equation WT = a.LT^b were estimated.     

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 to weight ratio of four fish species in estuary areas in the Northeast region of Brazil

The length to weight ratio (LWR) was used to estimate populations of four fish species sampled on the Amazon coast of the state of Maranhão, Brazil. The fishes were sampled in 2018 and 2019 by artisanal coastal fishing, using gillnets (0.20–0.60 mm). The parameters a and b of the equation W_T = a L_T^b were estimated. The obtained LWRs were W_T = 0.06LT^2.93, (r²) = .989 for Oligoplites saliens; W_T = 0.061L_T^2.57, (r²) = .982 for Peprilus crenulatus; W_T = 0.014L_T^2.80, (r²) = .985 for Bagre bagre; and W_T = 0.035L_T^3.21, (r²) = .981 for Nebris microps.     

Length–weight and length–length relationships of three fish species from the Yarlung Zangbo River in Tibet,China

Length–weight relationships and length–length were evaluated for three fish species (Schizopygopsis younghusbandi Regan, 1905; Ptychobarbus dipogon Regan, 1905 and Oxygymnocypris stewartii Lloyd, 1908) from the Yarlung Zangbo River in Tibet. Specimens were captured monthly using floating gillnets (mesh size 7.5 cm), bottom gillnets (mesh size 6.5 cm), and trap nets (mesh size 1.5 mm) from August 2008 to August 2009, March to August 2012, and March to April 2013. Regression coefficient (b) values of length–weight relationships (LWRs) ranged from 3.045 for P. dipogon to 3.193 for O. stewartii, whereas the a values ranged from 0.0040 to 0.0168 for O. stewartii and P. dipogon, respectively.     

Length‐weight relationships of Badis dibruensis Geetakumari and Vishwanath, 2010 (Badidae) and Lepidocephalichthys arunachalensis (Datta and Barman, 1984) (Cobitidae) from Subansiri River (Brahmaputra basin), Northeast India

Length–weight relationships (LWRs) for Badis dibruensis and Lepidocephalichthys arunachalensis, collected from the lower Subansiri River (Brahmaputra basin) in Assam, India from March 2016 to April 2017 using fishing gears namely cast nets (2.5 m, 1 m; 10–15 mm mesh size) and gillnets (30 × 0.9 m; 5–10 mm mesh size), are presented based on seasonal collections. The b values in the LWRs were determined as 2.56 for B. dibruensis and 3.28 for L. arunachalensis.     

Length–weight relationships of six fish species from the headstream region of the Dongjiang River,China

Dongjiang River, a main tributary of the Pearl River, is geographically situated in South China. The present study describes the length–weight relationships (LWRs) of six fish species (Acrossocheilus paradoxus, Barbodes semifasciolatus, Onychostoma elongatum, Microphysogobio fukiensis, Microphysogobio kiatingensis, Metzia lineata) from the headstream region of the river including five Chinese endemic species (A. paradoxus, B. semifasciolatu, O. elongatum, Mi. fukiensis, Mi. kiatingensis). Fish species of five genera of the same family were collected quarterly from April 2012 to October 2014 by using non‐selective fishing gears: drag nets (5 m, mesh‐size 3 cm), drift gillnets (30 × 15 m, mesh‐size 5 mm), fish cages (4 m, mouth opening 40 × 40 cm), scoop nets (mesh‐size 0.5‐1 cm), and electro‐fishing (12V, 200 Hz). The parameter a and b in the LWR equations (W = a L^b) ranged from 0.0014 to 0.0228, and 2.89 to 3.18, respectively. Compared with FishBase, this study provides the first LWR records for four cyprinids (A. paradoxus, B. semifasciolatu, O. elongatum, Me. lineata) and a new record of maximum body length for O. elongatum.     

Length–weight relationships of six elasmobranch species captured at the artisanal fishery of Margarita Island,Venezuela

This study reports the length – weight relationship (LWR) for five batoid and one shark species, all frequently captured by the artisanal commercial fishery on Margarita Island (10º44’ – 11º10’N and 63º46’ – 64º13’W), Venezuela. In 2013, elasmobranchs captured by the artisanal fleet (using bottom gillnets 200–400 m in length with 5–8 inch mesh size) were identified, sized, weighed and sexed. The value of a ranged from 0.0006 to 0.0351, meanwhile the b value ranged from 2.84 (for pooled Myliobatis freminvillei) to 3.39 (male Mustelus higmani), with r² ranging from 0.920 to 0.991. Differences in LWR due to sex were observed for three elasmobranch species. This study offers LWRs separate for males and females, also for species for which LWRs already exist and thus new knowledge is gained through the estimate presented here.     

Implications of climate change on the habitat shifts of tropical lizards

The effect of temperature on the distributions of ectothermic vertebrates is well documented. Despite the increase of 6°C expected in the next 60 years in South America, numerous vertebrates are still considered as ‘Least Concern’ species by the IUCN due to their large distribution, insufficient widespread threats and insignificant population decline. One example is the lizard Tropidurus torquatus (Squamata: Tropiduridae), commonly found thermoregulating in anthropic environments throughout the Brazilian Cerrado, but restricted to gallery forests in the equator‐ward localities. The urban areas in this warmer region have been colonised by other closely related congeners (e.g. Tropidurus oreadicus). This study aimed to understand this divergence of habitat selection by these tropirudids that may explain some of the species responses to past and future climate warming. We collected body temperatures (T_b), micro‐environmental temperatures (T_a) and operative (T_e) temperatures in four sites along a latitudinal gradient: a pole‐ward and two central sites where T. torquatus inhabit urban areas and one equator‐ward site where T. torquatus and T. oreadicus occur in the gallery forest and in urban microhabitats, respectively. All three populations of T. torquatus present similar T_b (35.5–36°C) and shared microhabitats with a similar T_a (34–37.3°C). The T_e in the equator‐ward urban site was considerably higher than in the gallery forest. Tropidurus oreadicus T_b was 38.2 °C (30.1–41.3°C) and was active at a T_a of 30.5–42.3°C. The overlap between the genus T_b, T_a and T_e highlights a decrease in the hours of activity that lizards would experience under climate warming. The reduction of hours of activity together with the devastation of natural habitats represents threats and an alarming scenario especially for the equator‐ward populations.     

Length–weight relationships of six fish species from mangroves of Qinzhou Harbor,Southern China

The length–weight relationships (LWRs) for six species were estimated. Fish were captured in the mangroves of Qinzhou Harbour, China, but also some specimens were purchased from fishermen. The sampling was undertaken monthly between May 2011 and April 2012 using seines (mesh size 5–10 mm; height 4 m; length 400 m) and traps (mesh size 8.5 mm; 35 cm² × 10 m for one unit) at seven sampling sites. Standard length was measured (precision 0.1 cm) and weight determined (precision 0.01 g) after preservation in formaldehyde (10%). Besides the equation parameters a (intercept) and b (slope) we determined also the 95% confidence limits for both parameters as well as the coefficient of correlation.     

Length–weight relationships of three fish species from the Yalong River,China

Length–weight relationships (LWRs) were determined for three fish species (Gymnodiptychus pachycheilus (Herzenstein, 1892), Triplophysa bleekeri (Sauvage & Dabry de Thiersant, 1874) and Triplophysa pseudostenura (He, Zhang & Song, 2012)) from the Yalong River in China. Samples were obtained between March 2009 and July 2013 using gillnets (25 × 12 m, mesh size 0.5 cm) and fish cages (0.5 × 0.5 × 10 m, mesh size 0.5 cm mesh). For each species, the sample size, length range, weight range, LWR, 95% confidence intervals of a and b, and coefficient of correlation were determined. Prior to this study, the LWRs for these three species were unknown.     

Length–weight relationships of three small indigenous fish species from the Lower Brahmaputra,India

Length–weight relationships (LWRs) for three small indigenous fish species from the lower Brahmaputra in Assam, India: Glyptothorax telchitta, Nangra assamensis, and Gudusia chapra were studied on a monthly basis from February 2015 to January 2016. Various fishing gear types were employed: cast nets (9′ ½”), gillnets (30 × 0.9 m, 0.5″; 60 × 3 m, 1.5″) and mosquito nets (20 × 6 m, 0.04″). No previous reference is available on LWR data for two of these species.     

Aspects of comparative thermal ecology of sympatric hinge-back tortoises (Kinixys homeana and Kinixys erosa) in the Niger Delta, southern Nigeria

Aspects of the thermal ecology of two sympatric hinge‐back tortoises, Kinixys erosa and Kinixys homeana, were studied in the rainforest zone of south‐eastern Nigeria (West Africa). There were no significant differences in mean body temperatures (T_b) among K. homeana males, K. homeana females, K. erosa males and K. erosa females. In both species, there was a significant correlation between T_b and air temperature (T_a), and the regression line of T_a plotted against T_b differed significantly from the line of ideal poikilothermy. These regressions did not differ significantly between sexes in either species. There were no significant differences in terms of mean T_b in K. homeana during the various day‐hour intervals, whereas the mean T_b of K. erosa varied significantly among the various daytime intervals, attaining the higher values at 11.01–15.00 and 15.01–19.00 hours. In both species, T_bs were nearly always below T_as, and the negative difference ‘T_b ‐ T_a’ increased with increasing T_a. The hourly‐time course of the difference between T_b and T_a showed significant differences in K. homeana (with the higher negative differences at 11.01–15.00 and 15.01–19.00 hours), whereas no such difference was observed in K. erosa. In general, tortoises of both species showed behavioural thermoregulation in their avoidance of overheating in tropical environments, taking advantage of shady forest environments.     

Reliable effective number of breeders/adult census size ratios in seasonal‐breeding species: Opportunity for integrative demographic inferences based on capture–mark–recapture data and multilocus genotypes

The ratio of the effective number of breeders (N_b) to the adult census size (N_a), N_b/N_a, approximates the departure from the standard capacity of a population to maintain genetic diversity in one reproductive season. This information is relevant for assessing population status, understanding evolutionary processes operating at local scales, and unraveling how life‐history traits affect these processes. However, our knowledge on N_b/N_a ratios in nature is limited because estimation of both parameters is challenging. The sibship frequency (SF) method is adequate for reliable N_b estimation because it is based on sibship and parentage reconstruction from genetic marker data, thereby providing demographic inferences that can be compared with field‐based information. In addition, capture–mark–recapture (CMR) robust design methods are well suited for N_a estimation in seasonal‐breeding species. We used tadpole genotypes of three pond‐breeding amphibian species (Epidalea calamita, Hyla molleri, and Pelophylax perezi, n = 73–96 single‐cohort tadpoles/species genotyped at 15–17 microsatellite loci) and candidate parental genotypes (n = 94–300 adults/species) to estimate N_b by the SF method. To assess the reliability of N_b estimates, we compared sibship and parentage inferences with field‐based information and checked for the convergence of results in replicated subsampled analyses. Finally, we used CMR data from a 6‐year monitoring program to estimate annual N_a in the three species and calculate the N_b/N_a ratio. Reliable ratios were obtained for E. calamita (N_b/N_a = 0.18–0.28) and P. perezi (0.5), but in H. molleri, N_a could not be estimated and genetic information proved insufficient for reliable N_b estimation. Integrative demographic studies taking full advantage of SF and CMR methods can provide accurate estimates of the N_b/N_a ratio in seasonal‐breeding species. Importantly, the SF method provides results that can be readily evaluated for reliability. This represents a good opportunity for obtaining robust demographic inferences with wide applications for evolutionary and conservation research.     

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 three fish species from the lower Brahmaputra drainage in Assam,India

Length‐Weight relationships (LWRs) for three Cyprinids (Chela cachius, Devario devario and Securicula gora) collected seasonally from May 2016 to January 2017 along the lower Brahmaputra drainage in Assam (Northeast India), using fishing gears [cast nets: 2.5 m, 10–15 mm mesh size; gillnets: 30 × 0.9 m, 18–20 mm mesh size], were estimated. The ‘b’ values of the LWR estimates ranged from 3.39 for C.  cachius, 3.14 for D.  devario, and 2.97 for S.  gora respectively.     

Length-weight relationships of 6 fish species caught in a Mediterranean lake (Trichonis-NW Greece)

In the present study the length–weight relationships (LWRs) of 6 fish species which are endemic to Western Greece, caught in the natural Lake Trichonis by experimental gillnets and electrofishing were estimated. Benthic (mesh size 5–55 mm; height 1.5 m; length 30 m) and pelagic (mesh size 6.25–55 mm; height 6 m; length 27.5 m) Nordic type multimesh gillnets were used seasonally, between February 2019 and November 2019, at different depth zones (0-57m). Electrofishing (80 Hz) conducted in the littoral zone of the lake during four samplings (2018, 2019). All the estimated LWRs were highly significant (p < .05) with high correlation coefficient (r² ≥ 0.962). The estimated b values ranged from 3.058 to 3.344. For five of the studied species (Trichonis spined loach (Cobitis trichonica Stephanidis 1974), Trichonis blenny (Salaria economidisi Kottelat 2004), Trichonis rudd (Scardinius acarnanicus Economidis 1991), Acheloos roach (Leucos panosi (Bogutskaya & Iliadou 2006)) , Hellenic minnowroach (Tropidophoxinellus hellenicus (Stephanidis 1971)) new maximum total body lengths (TL) were recorded, while for two species (T. hellenicus and L. panosi) LWRs are presented for the first time.     

Length–weight relationships for six fish species from the middle of the Yalu Tsangpo River,China

This paper reports the length–weight relationships for six fish species belonging to the Cyprinidae from the middle of the Yalu Tsangpo River in China. Samples were obtained by electroshock and drift net fishing techniques (mesh size 2 cm × 3 cm; 200 m net length) in April and September to October 2014. Length–weight relationships estimates for these species were not available in FishBase. A total of 737 specimens were used to estimate the a and b parameters. New maximum total lengths are also reported for six species. The r² values range from 0.98 to 0.99. Values of b vary from 2.88 to 3.19.     

Length–weight relationships for five fish species from the middle reaches of the Yangtze River,China

Length–weight relationships (LWRs) for five fish species which were captured by trap‐nets and gillnets (major mesh size: 1–10 cm) from the middle Yangtze River, China (29°47′ – 29°26′N; 112°51′ – 113°08′E) were determined in September 2017. These were Acheilognathus hypselonotus (Bleeker, 1871), Culter oxycephaloides Kreyenberg & Pappenheim, 1908, Distoechodon tumirostris Peters, 1881, Sarcocheilichthys nigripinnis (Günther, 1873) and Micropercops swinhonis (Günther, 1873). The LWRs were estimated using the logarithmic form of the formula W  =  a  ×  L^b. The b value ranged from 2.879 for A. hypselonotus to 3.285 for M. swinhonis. LWRs for four fish species and new maximum lengths for three species are presented to FishBase for the first time.     

Length–weight relationships for three fish species from the middle and lower reaches of the Jinsha River,China

This paper provides the length–weight relationships of three fish species from the middle and lower reaches of the Jinsha River, China. Samples were obtained seasonally during 2013~2016 using fishing gear (drift gillnets and di long) and electroshock fishing techniques (backpack electrofishing control unit powered by 12 V). For each species, the sample size, length range, weight range, LWR, 95% confidence intervals of a and b, and coefficient of correlation were determined. Length–weight relationship (LWR) for one species was unknown to FishBase and new maximum lengths were recorded for two species.     

Length–weight relationships of three fish species from the Tibet reach of the Lancang River,China

Length‐weight relationships (LWRs) were determined for three fish species, Schizothorax lantsangensis (Tsao, 1964), Schizothorax lissolabiatus (Tsao, 1964) and Schizopygopsis anteroventris (Wu & Tsao, 1989), from the Tibet reach of the Lancang River, China (N 29°06′–31°30′, E 96°57′–98°38′). Specimens were collected in April and September 2017. The specimens were caught with drifting gillnets (mesh size 2.5 cm and 7.0 cm). The b values of these three fish species ranged from 2.974 to 3.075. The high r² values (all > .980) indicate that these relationships will be appropriate for use in fisheries management of these species.