Estimation of relative growth of Minor carp Labeo bata (Cyprinidae) through multi‐linear dimensions

This study focuses on relative growth through length‐weight relationships (LWRs) and length‐length relationships (LLRs) using a total of 15 linear dimensions of Minor carp Labeo bata (Hamilton, 1822) from the Ganges River, northwestern (NW) Bangladesh. Also, meristic counts covering various fin rays and scales from different body parts (including lateral line scales) of L. bata (Hamilton, 1822) have been studied. A total of 300 individuals of L. bata were sampled occasionally from the Ganges River from July 2013 to June 2014, using various traditional fishing gears (e.g., Cast net, Gill net and Square lift net). Number of fin rays from all fins and scales were counted using magnifying glass. Additionally, a total of 15 different lengths were measured to 0.1 cm and whole body weight (BW) was taken to the nearest 0.1 g for each individual. Fin formula of L. bata is as follows: dorsal, D. 10–12 (i–ii/9‐10); pectoral, P₁. 12–16 (iii–iv/9–12); pelvic, P₂. 9 (i/8); anal, A. 6–7 (ii/4–5); and caudal, C. 20–24 (iv–vi/16–18), respectively. Minimum and maximum lengths were found as 8.0 to 25.1 cm in total length (TL) and body weight (BW) ranges from 4.8 to 161.0 g. All LWRs were highly significant (p < .001) with r² values ≥0.960. Based on r² value, LWR by BW versus TL was the best fitted model among 13 equations. In addition, the LLRs were also significant with r² values ≥ 0.959. According to r² value, LLR by TL versus FL was the best fitted model among 15 equations. This study would be very effective for species identification and stock assessment in the Ganges River, NW Bangladesh and surrounding ecosystems.     

Length–weight relationships of four indigenous fish species collected in Assam and Meghalaya,India

The length–weight relationships (LWRs) of four indigenous fish species; namely Parambassis baculis (Hamilton, 1822); Pethia gelius (Hamilton, 1822); Channa stewartii (Playfair, 1867); and Leiodon cutcutia (Hamilton, 1822) collected from the Ranganadi River in Assam, and the Simsang and Kynshi River in Meghalaya are presented in the present study. The value of the parameter b recorded for P. baculis = 3.347; P. gelius = 3.924; C. stewartii = 2.979; and L. cutcutia = 3.205, with regression coefficients (r²) of 0.993, 0.963, 0.983 and 0.955, respectively. Parameter a was 0.0124 for P. baculis, 0.0037 for P. gelius, 0.0098 for C. stewartii and 0.0273 for L. cutcutia. As information on the LWRs of these fish species is not available in the FishBase database, it should assist future researchers to better analyse the stock of these fishes.     

Biological aspects of Schilbe intermedius (Ruppell, 1832) in the Nyanza Gulf of Lake Victoria,Kenya

Silver butter catfish (Schilbe intermedius) is an indigenous fish species in Lake Victoria. It has a good economic value because of the quality and freshness of its flesh, increasing its demand for consumption. It is potamodromous, with its stock in the lake declining because of overexploitation by the use of illegal fishing gears at the river mouths on their way to spawning areas. Fish samples (321) were obtained from commercial gill net (1.5–3 in.) fishers within Nyanza gulf. The fish samples were weighed (g) and measured (cm), dissected and sex determined by visual inspection of the gonads. Ovaries for mature female fish specimens were preserved for analysis of fecundity. Fecundity was determined by the gravimetric technique. The mean (±SE) length and weight for all fish were 18.2 ± 0.2 cm TL and 51.9 ± 1.9 g, respectively. The female fish (20.0 ± 0.2 cm) were significantly (F = 199.80, p < .05) larger than the males (15.9 ± 0.1 cm). Similarly, the females (68.8 ± 2.6 g) were significantly (F = 152.61, p < .05) heavier than the males (30.93 ± 1.02 g). The overall sex ratio was 1.23:1.0 (female:male). The length frequency exhibited a unimodal distribution, with the modal class between 16 and 18 cm for either sex. The regression slope (b) of the length–weight relationship was 3.2, 3.1 and 3.0 for all fish, females and males. The absolute fecundity ranged from 6,510 to 59,818 eggs, with a mean of 34,473 eggs. The length at 50% maturity was estimated to be 16.0 cm (female) and 18.0 cm (male) fish. The mean length and size at maturity of S. intermedius have declined, likely attributable to fishing effects, changes in food resources, competition and predation. Thus, the present study provided relevant biological data of S. intermedius, which is currently limited for this region.     

New maximum size record,length–weight relationships and form factor of Hooghly Croaker Panna heterolepis Trewavas, 1977 from the Bay of Bengal (Bangladesh)

The present study analysed the length–weight relationships (LWRs) and form factor (a_3.0) of Panna heterolepis Trewavas, 1977 from the Bay of Bengal, Bangladesh. A total of 316 specimens were sampled during the pre‐monsoon (n = 96), monsoon (n = 116) and post‐monsoon (n = 104) season (March 2018–February 2019) using a Seine bag net. Individual total length (TL) and body weight (BW) were measured with a measuring board and digital weight balance, respectively. The TL vs. BW relationship indicated a negative allometric growth for P. heterolepis. The present study also provides LWR, a_3.0 (0.0070) and a new maximum recorded size (29.50 cm TL and 24.50 cm SL) of P. heterolepis for the first time, data currently lacking in the FishBase online database. The results of the present study will be helpful for stock assessment and management of this fish in the Bay of Bengal, Bangladesh and neighbouring countries.     

Ontogenic Changes in Prey Ingested by Nile perch (Lates niloticus) Caught in Nyanza Gulf of Lake Victoria,Kenya

A total of 289 fish were analysed in this study, with Caradina nilotica (44%) being the dominant food item in their diet, while tilapia (8%) contributed the least. Haplochromines, unidentified fish prey and juvenile Nile perch also were observed. An ontogenic shift was observed, with C. nilotica contributing highest (61.1%) of the diet of fingerlings, but decreasing to 21% in the diet of adults. Nile perch contributed 35.7% of the diet in the adults and 8.1% in the fingerlings. This study indicates Nile perch is a predatory fish, feeding mainly on C. nilotica, haplochromines, tilapia, Nile perch and other fish materials.     

Length–length and length–weight relationships for 48 fish species from reservoirs of the Paraná State,Brazil

Length–length and length–weight relationships was estimated for 48 fish species collected in 30 neotropical reservoirs located in the State of Paraná, Brazil. Significant relations were found for all species. The values of the parameter slope (b) in the length–weight relationship ranged from 2.49 to 3.46 for grouped sexes, and from 2.66 to 3.15 for separated sexes. Differences between sexes (indication of sexual dimorphism) were verified for 20 species. Males exhibited greater lengths than females for Astyanax janeiroensis, Bryconamericus iheringii, Geophagus brasiliensis, Glanidium ribeiroi and Hypostomus derbyi, whereas females attained greater lengths than males for the other 15 species examined in this study.     

Bacterial abundance on the skin,gills and intestines of Cyprinus carpio in Lake Naivasha,Kenya: Implications for public health and fish quality

Cyprinus carpio is the most important fish species in the Lake Naivasha fishery, comprising 51% of the total catch in the lake. Microflora, especially enteric bacteria of human or animal origin, are the causative agent for fish contamination and spoilage. Poor sanitation standards and poor sewage treatment and disposal methods within Lake Naivasha and its catchment pose a great threat for degrading the quality of C. carpio. The potential impact is rejection of the fish in the local, regional and international markets, risking the collapse of the Lake Naivasha fishery. This study determined the bacterial quality of water and C. carpio from three different sites within Lake Naivasha, namely Malewa River mouth, sewage discharge point and a mid‐lake site, based on plate count techniques. Physicochemical parameters characterizing the lake water also were also measured in situ. This study results indicated that both the fish and water in Lake Naivasha exhibited poor bacterial quality. All the physicochemical parameters were within the recommended range for fish culture, although they also were conducive to the proliferation of bacteria. Most of the sampling sites exhibited significant spatial variation in their bacterial abundance (P < 0.05). The sewage discharge sampling site exhibited the highest mean density values for bacterial densities and clearly degrade the quality of the fish in the lake. Proper sewage treatment, and the installation of modern sanitation facilities, is recommended to improve the bacterial quality of the fish.     

Population Biology of Nile tilapia (Oreochromis niloticus) in Lake Naivasha,Kenya

The Nile tilapia (Oreochromis niloticus) was introduced into Lake Naivasha to provide exploitable fisheries, being one of the commercially important fish providing livelihoods to communities around the lake. Its stocks in the lake have been declining, however, because of intense fishing, ecological changes and effects of other exotic species. The present study was undertaken to investigate the population and biological parameters of Oreochromis niloticus. Fish samples (1,021) were caught monthly from January to December 2017, collecting a total of 1,021 O. niloticus, with an overall sex ratio of 2.21:1.0 (male: female). The length of the fish ranged from 9.0 to 40.0 cmTL and weighed between 20 and 1,220 g. The mean length and weight for all fish was 22.6 cm and 272.6 g. The slope b of length–weight relationship was 2.86 for all fish, indicating negative allometry. The mean condition factors were 0.99, 1.04 and 1.01 for male, female and all fish, respectively. The length at first maturity (Lm₅₀) was estimated to be 28.0 cmTL for all sexes, indicating the fish matures at smaller sizes. The length at first capture (Lc₅₀) was calculated to be 19.38 cm, a value much lower than its Lm₅₀, reflecting the capture of juvenile fish. The asymptotic length (L∞) was 42 cm, the growth coefficient (K) was 0.21/year, and the growth performance index (Ф) was 2.57. The natural (M), fishing (F) and total mortality (Z) coefficients were estimated to be 0.55, 0.26 and 0.80/year, respectively. The optimum sustainable yield (E_0.5), maximum sustainable yield (E_max) and maximum economic yield (E_0.1) indices of 0.23, 0.35 and 0.26, respectively, imply an optimal exploitation of O. niloticus. The results of the present study provided some important insights into the biology and management needs of the O. niloticus fishery in Lake Naivasha, as well as revealing a gap for further research on its reproductive biology.     

Aspects of the biology of Labeo cylindricus (Pisces: cyprinidae) in Lake Baringo,Kenya

Aspects of the biology of Labeo cylindricus from Lake Baringo were investigated, based on experimental beach seining and gillnetting between August and October 2007. The length–weight relationship indicated the species exhibited positive allometric growth (b = 3.7083), with a condition factor (K) of 0.84 ± 0.0298 S.D. Males dominated fish catches, with an adult sex ratio of males/females of 1:1.7. The fish length‐at‐50% maturity (Lm50) was 127.7 and 126.1 mm total length (TL) for males and females, respectively. Fish age and growth were determined from sagittal otoliths considered to be from the young‐of‐the‐year. Clear circuli observed in the otoliths were used to determine fish age in days. Validation by oxytetracycline marking indicated that a single growth increment (1.1 ± 0.1 SE) is formed daily on fish otoliths. Fish length (TL mm) was correlated significantly with age (in days), TL = 1.398 Age + 26.523 (r² = 0.91). Fish growth was subsequently estimated to be 1.398 mm day^?1. The weights and ages (in days) of fish exhibited a significant (P < 0.05) power relationship defined by the equation: W = 0.0003 Age^2.5804 (r² = 0.88). The results of this study provide parameters that, if appropriately monitored, can be used to predict responses of fish populations in Lake Baringo and elsewhere to human interventions (exploitation) and natural environmental change.     

Population characteristics of five major commercial fish species of the Tono Reservoir in northern Ghana

Five major commercial fish species, comprising Sarotherodon galilaeus, Oreochromis niloticus, Coptodon zillii, Clarias gariepinus and Auchenoglanis occidentalis of the Tono Reservoir fishery, were studied from January, 2015 to December, 2016 using length‐based models to establish the state of the stocks. Routines in the FAO‐ICLARM Stock Assessment Tools II (FISAT II) were used to determine the growth and mortality parameters, exploitation rates (E) and recruitment patterns of the length–frequency data generated from commercial fish landings and experimental catches. The growth coefficients (K) of the five fish species ranged 0.48–4.89 per year; asymptotic lengths (L_∞) ranged from 18.38 to 76.16 cm; and hypothetical ages (t₀) ranged between 0.03 and 0.28 years. All five fish species were exploited above the optimal exploitation rate (E_opt = 0.5), indicating overfishing of the species. There was a year‐round recruitment, with major and minor peaks corresponding with the major and minor spawning seasons. Fishing gear regulation and community‐based co‐management system were some management options recommended to enhance sustainable exploitation and management of the fishery.     

Growth,mortality and recruitment of silver cyprinid (Rastrineobola argentea) in the open waters of Lake Victoria,Kenya

This study investigated the growth, mortality and recruitment of Rastrineobola argentea in Lake Victoria on the basis of length–frequency data collected during the period 2014–2015. The asymptotic length (L _∞ ) had a mean (±SE ) value of 53.50 ± 0.50 mm SL , growth curvature (K ) of 0.81 ± 0.06 year^?1, total mortality (Z ) of 2.96 ± 0.12 year^?1, a natural mortality (M ) of 1.23 ± 0.06 year^?1, a fishing mortality (F ) of 1.74 ± 0.07 year^?1, an exploitation rate (E ) of 0.59 ± 0.01, a growth performance index (?′ ) of 3.36 ± 0.02 and a length at 50% capture (L ₅₀) of 28.25 ± 0.43 mm SL . The fish exhibited a peak breeding during the months of May and August. The Beverton and Holt relative yield‐per‐recruit model indicated mean (±SE ) indices as 0.37 ± 0.01 for optimum sustainable yield (E _0.5), 0.76 ± 0.01 for maximum sustainable yield (E _max) and 0.66 ± 0.01 for economic yield (E _0.1). Compared with previous studies, there is a great decline in the sizes of R. argentea stocks in Lake Victoria. Thus, management measures should include restriction on illegal seine nets <10 mm mesh size and re‐enforcement of a fishing ban or a closed season.     

黄河下游支流大汶河鱼类多样性及影响因子分析

为了解黄河下游支流大汶河鱼类多样性及其与环境因子的关系，分别于2017年4月和10月对大汶河24个采样点进行鱼类及环境调查，采用冗余分析方法识别了影响大汶河鱼类个体数量和多样性指数的主要环境因子。结果表明:2017年共采集到鱼类8 299尾，隶属于4目16科25种，其中鲤科鱼类共15种；鱼类多样性和均匀性较差，优势种以鲫(Carassius auratus)、(Hemiculter leucisclus)和乌鳢(Channa argus)等耐受性较强的平原性鱼类为主；大汶河鱼类物种数量、生物量和多样性指数的季节性变化不显著，但是秋季个体数量显著大于春季；影响大汶河鱼类个体数量的主要环境因子是水深和河宽，而影响鱼类多样性指数的主要环境因子是DO。     

扑草净对鲫鱼（Carassius auratus）生长的影响及其导致的水体营养盐变化

为评价扑草净在水环境中造成的生态风险,以扑草净作为目标污染物,以鲫鱼作为受试生物,于实验室内水族箱中进行试验。持续监测鲫鱼体质量体长及水体营养盐浓度,考察扑草净对鲫鱼生长的影响,及其导致的水体营养盐浓度变化特征。结果表明：鲫鱼体质量生长率、体长生长率及营养盐浓度随时间的变化可利用Logistic方程描述（R²=0.959~0.997）;有扑草净组鲫鱼体质量生长率等比无扑草净组低8.7%～50.3%。无鱼时扑草净对水体中氮磷营养盐浓度、营养盐比例及总氮/总磷比例无显著影响;有鱼时,有扑草净组的总颗粒氮和总颗粒磷浓度分别比无扑草净组低41.4%及33.8%,有无扑草净组各形态磷营养盐浓度与总磷的比例以及总氮/总磷浓度比例差异显著。研究表明扑草净对鲫鱼的毒性效应可间接影响水体营养盐浓度。     

Gillnet selectivity estimates for five commercially important fish species in Tono Reservoir,Northern Ghana

Gillnet selectivity is crucial for the effective and sustainable management of fisheries. However, there is inadequate information on gillnet selectivity for commercially important species in Tono Reservoir. To facilitate the sustainable exploitation of fish species, this study was conducted to estimate the selectivity parameters of commonly used monofilament gillnets for commercially important fish species in Tono Reservoir from January 2015 to June 2016. Two common nylon monofilament gillnets used by fishermen in Tono Reservoir with stretched mesh sizes 5 and 7 cm and equal dimensions were placed in the same fishing area and retrieved within 12 h. The fish catches were assessed, and selectivity parameters for Sarotherodon galilaeus, Oreochromis niloticus, Coptodon zillii, Clarias gariepinus and Auchenoglanis occidentalis were estimated using the Holt model. The catch per unit effort of the two gillnets exhibited no significant difference. The optimum total lengths of capture of four fish species excluding C. zillii ranged from 13.53 to 25.43 cm for the 5 cm gillnet, and 18.95 to 35.60 cm for the 7 cm gillnet. Common selection factors varied from 2.71 to 5.09. The mean total length at first sexual maturity for all five fish species ranged from 8.60 to 28.86 cm. Both the 5 and 7 cm gillnets were found to be inappropriate for use in the reservoir. Accordingly, their use should be discouraged to protect juvenile fish so that the sustainable exploitation and conservation of fish species in this multispecies fishery can be achieved.     

Sex ratio and reproduction of invasive red devil, (Amphilophus labiatus: Cichlidae) in Lake Sentani,Indonesia

The Red Devil Cichlid Amphilophus labiatus (Günther 1864), native to Lake Nicaragua and Lake Managua in Central America, is widely cultivated as an attractive, yet aggressive, aquarium fish that has been introduced to several freshwater locations around the world. It was recently introduced into Lake Sentani in Indonesian New Guinea, a naturally rich aquatic habitat home exhibiting a diverse fauna with high endemism. To better understand the invasive potential and impacts of A. labiatus, the present study was undertaken to describe the sex ratio and reproductive potential of A. labiatus in Lake Sentani through determination of its gonad maturation stages, gonado‐somatic index and fecundity. The fish were collected using floating gill nets at six locations around the lake between June and August 2019. Sex identification, gonads type, gonad stage and weight, fecundity were observed in the laboratory. Of the total 542 of A. labiatus collected during the survey, 345 individuals were sampled for sex ratio and reproduction. The overall male:female ratio was skewed towards males in a ratio of 3.28:1. The males were generally found to be in the gonad maturation stage I, while the females were commonly found in gonad maturation stages III and IV for all sampling locations during the study period. The highest male mean GSI value was found for the Yakonde site (0.24 ± 0.21) and at the Ayapo site (1.11 ± 1.01) for the females, with a fecundity of 191–2,720 eggs. The fish have spread to most parts of the lake, being conditioned to potentially spawn at any location, thereby providing an explanation for the observed rapid increase of the A. labiatus population over the last ten years. The results of the present study suggest a high invasive potential for this species in this and other similar lake habitats, warning that their careful management should be undertaken to restrict their further spread in Indonesia and elsewhere.     

Identification of critical control points using water quality as an indicator of hygiene for artisanal fisheries on Lake Malawi

Fish are a highly perishable commodity, and unhygienic fresh fish supply chains have been documented over the past two decades in sub‐Saharan Africa. Fishers spend long hours on boats with no provision of sanitary facilities, and even after landing, they are often in environments without sanitary facilities. The purpose of the present study was to explore the impacts of water, sanitation and hygiene practices in an artisanal fishery on food safety by analysing water samples in close contact with fresh fish at various checkpoints from capture to sale at the local market along the shores of Lake Malawi (Malawi). The four checkpoints included (a) fishing boats at the fishing ground before fishing commenced (n = 85); (b) in the same boats at the landing site before offloading fresh fish (n = 85); (c) with fresh fish transporters at the landing site (n = 71); and (d) among vendors at the market (n = 63). Escherichia coli was found in a high percentage of samples at each of the four checkpoints during the dry, wet and cold seasons. The highest risk for contamination (represented by E. coli concentrations) was the transition from transport to vendor, regardless of the season during which the samples were taken. The product value chain demands food safety. The results of the present study have potential applications in informing future interventions to develop behavioural change strategies regarding handwashing and toileting practices, norms unique for highly mobile fishing communities through the integration of hardware and software solutions and using better‐quality water to store fish on the boat, in transport and at the market.     

Numerical expressions of otolith shape and morphometric relationships for five fish species in tidal‐linked lagoons in the northern Arabian Sea

Otoliths from five fish species, including Acanthopagrus latus, Daysciaena albida, Ellochelon vaigiensis, Mugil cephalus and Mystus gulio, were used to develop numerical expressions involving otolith shape indices and morphometric parameters. A total of 342 fish specimens in lagoons (24°39′ 0N, 68°50′0E) were sampled from August 2014 to July 2015. A linear model related to fish sizes, otolith sizes and weights were applied, with estimated coefficients of determinations (r² = 0.99–0.53). Otolith shape indices, including form factor, roundness, aspect ratio, circularity, rectangularity and ellipticity for each fish species, also were analysed. The results of the present study are the first to describe relationships between otolith dimensions, fish morphometrics and shape indices of highly valued fish species and can be an important input for further trophic modelling to study food web dynamics.     

Some aspects of the biology of Nile perch,Lates niloticus,in the open waters of Lake Victoria,Kenya

Samples (6404) of Nile perch were collected monthly from commercial catches between June 2014 and June 2015. The total length (cm), weight (g) and sex of fish were all determined in the field, with 3771 (59%) being male and 2059 (32%) being female fish, for an overall sex ratio of 1.83:1.00 (male: female). The average length and weight for all fish were 55.38 ± 0.14 cm TL and 2355.10 ± 22.30 g, respectively. The size of male fish ranged from 15.5 to 128.5 cm TL and weighed between 190 and 25 000 g, whereas that of female ranged from 21.0 to 130.0 cm TL and weighed between 124 and 25 800 g. The value of the regression slope b of the length–weight relationship was equal to 3.04. The mean (±SD) condition factor for all fish was 1.23 ± 0.13. The condition factor was different in the length groups, with the highest (1.32 ± 0.13) and lowest (1.12 ± 0.20) values recorded in length groups 100–110 and <30 cm TL, respectively. The highest and lowest condition factors were recorded between January and March, respectively. The length–weight relationship and condition of Nile perch in Lake Victoria have deteriorated greatly, this finding being linked to the reduction of its prey species in the lake.     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.