Length‐weight relationships for five fishes in the Pengxi River,a main tributary of the Three Gorges Reservoir,China

The length‐weight relationships and new total length are described for five fish species in the Pengxi River basin of the Three Gorges Reservoir. Fish were occasionally sampled from five sites between 2009 and 2014, using various gill nets (mesh size range 2–12 cm) and electrofishing. For four of the five species studied a new maximum total length not yet recorded in previous length‐weight estimates have been found. These data will help to convert length data from field studies in the Three Gorges Reservoir into weight and biomass.     

Feeding chronology of juvenile piranhas,Pygocentrus notatus,in the Venezuelan llanos

Synopsis During the 1988 rainy season, I studied the 24 h feeding chronology of juvenile (40–68 mm standard length) piranhas, Pygocentrus notatus (Characidae: Serrasalminae) from a natural population inhabiting a small savanna stream in Apure State, Venezuela. Stomach contents analyses, supported by laboratory determinations of digestion rate, showed that these fish are primarily diurnal carnivores. Predatory activity on 4–5 August 1988 increased markedly after sunrise, peaked around 1100 h, and essentially stopped after sunset. Means of stomach content weight-to-fish weight ratios among the periods sampled were significantly different. Small fish were the major prey at all hours (81% of total prey volume). Underlying factors responsible for the observed 24 h feeding patterns were not investigated, but avoidance of predation by adult piranhas, which were very active near sunset, may have been important.     

Hydrology and underwater climate of the Banc d'Arguin,Mauritania: a review

The northern coast of Mauritania between Cap Blanc and Cap Timiris is characterized by a large variety of hydrological situations. At the western slope of the Banc d'Arguin, at a depth of about 20 m, the underwater climate is essentially of a temperate character. This is a highly unstable area due to the occurrence of upwellings and the movements of the intertropical front. Close to the coast the isolation of water masses by the very shallow Banc d'Arguin results in an increase of temperature and salinity. These factors show a gradient towards the South from Cap, St. Anne to the islands. In this region the underwater climate is tropical, a feature which is most clearly expressed in land-locked bays such as the Baie d'Arguin, the area around the island of Tidra, and the Baie de St. Jean. In the latter bay the conditions are most extreme (salinity > 80). Due to the coastal topography the area of the islands around Tidra is highly isolated. This area receives no fertilization from the upwellings offshore.     

Abundance and distribution of inshore fish in fished and protected areas in Lake Kariba,Zimbabwe

Abundance and size distribution of inshore fish populations was assessed by fishing with standard Lundgren survey gill-nets in areas open to fishing and reserved areas that are protected from fishing activities.The direct gradient analysis technique — Detrended Canonical Correspondence Analysis — revealed that fish abundance and their composition in Lake Kariba are strongly structured by lake morphometry.The comparison between fished and reserve areas showed that there was a significant reduction in mean length of commercially fished species in the fished areas and the size distribution curves were skewed, lacking small and large length classes. There was a higher abundance of non-commercial species in the fished areas. It was also revealed that the mochokid Synodontis zambezensis Peters 1852, was the most abundant species and was present at all depths sampled in all the stations.There were indications that non-commercial species were important in terms of abundance in the fished areas. These included S. zambezenzis, Schilbe intermedius (Ruppell, 1832) and other smaller species. This was attributed to them being selected against in the gill-nets.     

Food and feeding relationships of young fish in the first weeks after the beginning of exogenous feeding in Lake Opinicon,Ontario

Synopsis Young fish of six species in an open water community all began their exogenous feeding by taking nauplii and small cyclopoids of body length (less tail) of 0.1–0.3 mm. Appearance of larvae of the different species in the system was, however, sequential, the resource being utilized by the different species in turn. The sequence was: Perca flavescens, Percina caprodes, Pomoxis nigromaculatus, Ambloplites rupestris, Lepomisgibbosus and L. macrochirus.The larvae and juveniles changes their diet rapidly as they grew. Fish 10–14 days after hatching and 8–10 mm in length i.e. close to the beginning of the juvenile period, consumed larger-bodied prey items (including several genera of Cladocera) and had more diversified diets than the 4.5–6.0 mm first-feeding larvae. These differences, and progressive dispersal of the larger young from the area, served to minimize the chances of food competition between batches of young of different ages.The composition of the fish community of larvae changed from week to week as new species entered it, increased in size and departed. Patterns of food utilization changed accordingly.Numbers of cyclopoids, their nauplii, and Bosmina longirostris, fell rapidly in May — early June, and did not increase again until August. These changes coincided with the rise and fall in numbers of the young fish in the habitat.Paper presented in the symposium \lsEmbryonic and larval periods of fishes: present status and significance\rs, Canadian Conference for Fisheries Research (CCFFR), Fredricton, New Brunswick, January 1977.     

Predictability of littoral-zone fish communities through ontogeny in Lake Texoma,Oklahoma-Texas,USA

Synopsis We sampled larval, juvenile and adult fishes from littoral-zone areas of a large reservoir (Lake Texoma, Oklahoma-Texas) (1) to characterize environmental factors that influenced fish community structure, (2) to examine how consistent fish–environment relationships were through ontogeny (i.e., larval vs. juvenile and adult), and (3) to measure the concordance of larval communities sampled during spring to juvenile and adult communities sampled at the same sites later in the year. Larval, juvenile and adult fish communities were dominated by Atherinidae (mainly inland silverside, Menidia beryllina) and Moronidae (mainly juvenile striped bass, Morone saxatilis) and were consistently structured along a gradient of site exposure to prevailing winds and waves. Larval, juvenile and adult communities along this gradient varied from atherinids and moronids at highly exposed sites to mostly centrarchids (primarily Lepomis and Micropterus spp.) at protected sites. Secondarily, zooplankton densities, water clarity, and land-use characteristics were related to fish community structure. Rank correlation analyses and Mantel tests indicated that the spatial consistency and predictability of fish communities was high as larval fishes sampled during spring were concordant with juvenile and adult fishes sampled at the same sites during summer and fall in terms of abundance, richness, and community structure. We propose that the high predictability and spatial consistency of littoral-zone fishes in Lake Texoma was a function of relatively simple communities (dominated by 1–2 species) that were structured by factors, such as site exposure to winds and waves, that varied little through time.     

Length‐weight relationships of 29 fish species from the Tucuruí Reservoir (Tocantins/Araguaia Basin,Brazil)

The length‐weight relationships (LWRs) are described for 29 fish species in the region of the Tucuruí Reservoir, located in the Tocantins/Araguaia Basin, northern Brazil. Fishes in fourteen sites were sampled seasonally for 10 years, from 2001 to 2010. Significant differences between sexes were found for two species, while 27 species had similar LWRs for males and females. The relationship of standard length and total length is presented for all species as well as the minimum and average size of reproductive females and seasonality of occurrence. No information on LWRs of these 29 species was heretofore available in FishBase.     

The occurrence and significance of Cladocera (Crustacea) in some streams of Central Indiana,U.S.A.

Although Cladocera are collected often in large rivers, their importance in streams has been under-estimated. This paper summarizes the results of a preliminary study of the benthic Cladocera in the streams of three watersheds in South Central Indiana. Seventeen sites were sampled with respect to species of benthic Cladocera present, their relative abundance, population size, and population dynamics.Cladocera were present in all streams and sites in the three watersheds. Nineteen species were collected: 13 species from the family Chydoridae, 3 Daphniidae, 2 Macrothricidae, and 1 Bosminidae. Just four species — Alona circumfimbriata, Chydorus brevilabris, Pleuroxus denticulatus, and Macrothrix laticornis — made up 68–96% of the numbers at all sites.Density of Cladocera ranged from 3–5200 m^–2 and they reproduced and maintained populations in the streams sampled. Numbers were generally high in October and early November and decreased to near zero in late December and January. The most important factor appearing to affect population sizes was discharge. Numbers at almost all sites decreased significantly after a rainfall increased discharge.A Principal Components and clustering analysis grouped sites with similar physical parameters in a continuum of low to high order. Sites with low numbers of Cladocera were generally shallow, narrow, and had a loose unconsolidated substrate. Sites with high population numbers were generally deep, wide, and had a stable substrate that accumulated detritus.     

Morphometric analysis of otoliths of juvenile crucifix sea catfish Sciades proops (Valenciennes, 1840)

The objective of this study was to analyze the morphometry of otoliths for Sciades proops juveniles by testing the hypothesis of equality in morphometric relationships for the right and left otoliths, which could then be interchangeably used to estimate fish size or weight. Samples were obtained monthly directly from anglers after each event that took place off the state of Sergipe from March/2014 to April/2015. Anglers used rod and reel during these events, with no restriction on hook size or line thickness. Each fish specimen sampled had their total weight (W, g) and total length (TL, cm) measured and their lapillus otoliths removed and stored separately. Each otolith had its length (OL), width (OWi), and thickness (OT) measured (all in mm) under a stereomicroscope. Otoliths were weighed using a precision scale (OW, g). A total of 883 specimens were sampled: TL = 12.0–60.5 cm and W = 9.8–1880 g. The weight‐length relationship for the juvenile fishes was W = 0.0052TL^3.086 and for their otoliths was OW = 0.0002OL^3.177. The weight‐length and length‐length relationships fitted for each otolith (right and left) were not statistically different and thus all relations were estimated for grouped otoliths. The length‐length relationships for the otoliths were: OWi = 0.947OL?0.205 and OT = O.484OL?0.698. The relationship estimated for juvenile fish and otolith weight was Wj = 1076.1OW?9.120. For juvenile fish total length and otolith length, width and thickness, the following relationships were estimated: TLj = 4.028OL?3.199, TLj = 4.208OWi?2.091, and TLj = 7.824OT + 3.659, respectively. Relationships between fish and otolith size, and between fish and otolith weight indicated a change in slope close to L_m50, which should be better explored when more adult specimens are available.     

The effects of turbidity and vegetation on the risk of juvenile salmonids, Oncorhynchus spp., to predation by adult cutthroat trout, O. clarkii

Synopsis During their seaward migration, juvenile salmonids encounter structural and visual cover which varies between and within watersheds. In this study, the effects of two types of cover (turbidity and artificial vegetation) on the predation mortality of juvenile salmonids exposed to fish piscivores was investigated in outdoor concrete ponds. During experiments, adult coastal cutthroat trout, Oncorhynchus clarkii clarkii, were allowed to feed on juvenile salmonid prey — chinook salmon, O. tshawytscha, chum salmon, O. keta, sockeye salmon, O. nerka, and cutthroat trout — in separate trials. Daily instantaneous per capita predation rate was determined for each turbidity and vegetation treatment, within each trial. Mean predation rates varied between 1% and 76% daily. In the presence of cover, mean daily predation rates were 10–75% lower than those in controls (no vegetation and clear water), depending on prey species. Predation rates were significantly lower in the presence of vegetation cover and did not covary with prey size or species. The effects of turbidity were generally not significant and were not additive with the effects of vegetation. However, turbidity appeared to significantly reduce the effectiveness of vegetation as cover for juvenile chinook and sockeye salmon. We suggest that these two forms of cover do not affect risk of predation by fish piscivores to juvenile salmonids via the same mechanism.     

VIS – A database on the distribution of fishes in inland and estuarine waters in Flanders,Belgium

The Research Institute for Nature and Forest (INBO) has been performing standardized fish stock assessments in Flanders, Belgium. This Flemish Fish Monitoring Network aims to assess fish populations in public waters at regular time intervals in both inland waters and estuaries. This monitoring was set up in support of the Water Framework Directive, the Habitat Directive, the Eel Regulation, the Red List of fishes, fish stock management, biodiversity research, and to assess the colonization and spreading of non-native fish species. The collected data are consolidated in the Fish Information System or VIS. From VIS, the occurrence data are now published at the INBO IPT as two datasets: ‘VIS - Fishes in inland waters in Flanders, Belgium’ and ‘VIS - Fishes in estuarine waters in Flanders, Belgium’. Together these datasets represent a complete overview of the distribution and abundance of fish species pertaining in Flanders from late 1992 to the end of 2012. This data paper discusses both datasets together, as both have a similar methodology and structure. The inland waters dataset contains over 350,000 fish observations, sampled between 1992 and 2012 from over 2,000 locations in inland rivers, streams, canals, and enclosed waters in Flanders. The dataset includes 64 fish species, as well as a number of non-target species (mainly crustaceans). The estuarine waters dataset contains over 44,000 fish observations, sampled between 1995 and 2012 from almost 50 locations in the estuaries of the rivers Yser and Scheldt (“Zeeschelde”), including two sampling sites in the Netherlands. The dataset includes 69 fish species and a number of non-target crustacean species. To foster broad and collaborative use, the data are dedicated to the public domain under a Creative Commons Zero waiver and reference the INBO norms for data use.     

Preserving young‐of‐the‐year Perca fluviatilis in ethanol,formalin, or in a frozen state and the consequences for measuring morphometrics

As it is often not possible to immediately analyse individuals sampled in the field, captured fish are preserved and stored for later investigation. The objective of this study was to assess the effects of various preservation methods on subsequent changes in morphometric parameters while also providing correction factors to re‐calculate the original body dimensions when sampled fish are measured at a later date. In this study, juvenile perch (Perca fluviatilis, 66.5 ± 10.2 mm total length) were measured directly after capture, then either frozen at ?20°C, preserved in 70% ethanol, or in 4% formalin. They were again measured after 24 h, 3 days, 7 days, and thereafter on a weekly basis for 8 weeks. Ethanol‐preserved perch greatly decreased length and weight; formalin preservation also led to a comparable length reduction, but increased the weight of the perch. In contrast, frozen perch showed less shrinkage and only moderate weight loss. Of the three preservation methods, freezing clearly caused the fewest distortions. Hence, freezing is recommend as the most preferable preservation method, especially in multi‐disciplinary studies on fish ecology; for all other preservation methods the correction factor over time will have to be pre‐determined for each species and size class.     

Length–weight relationships of 19 freshwater fishes from the Upo Wetland in South Korea

The length–weight relationships (LWRs) for 19 freshwater fish species in Upo Wetland, South Korea, were analyzed. Fish samples were collected quarterly using scoop‐nets (5 mm mesh), casting nets (7 mm mesh) and a fixed shore net (15 mm mesh) from 2007 to 2014. LWRs data for three species have not yet been listed in FishBase.     

Length–weight and length–length relationships for 135 fish species from the Xingu River (Amazon Basin,Brazil)

Length–weight (LWR) and length–length relationships (LLR) are presented for 135 freshwater fish species sampled by several types of fishing gear between April 2012 and July 2014 in the middle and lower Xingu River Basin, northern Brazil. The report represents the first references on LWRs and LLRs for 114 and 119 species, respectively, and also provides a new maximum size for 96 species.     

Using Fish Population Metrics to Compare the Effects of Artificial Reef Density

Artificial reefs continue to be added as habitat throughout the world, yet questions remain about how reef design affects fish diversity and abundance. In the present study, the effects of reef density were assessed for fish communities and sizes of economically valuable Lutjanus campechanus 13 km off Port Mansfield, Texas, at a reef composed of more than 4000 concrete culverts. The study spanned from May to June in 2013 and 2014, and sites sampled included natural reefs, bare areas, and varying culvert patch density categories, ranging from 1–190 culverts. Abundances of adults and species evenness of juvenile populations differed between the years. Fish communities did not significantly differ among density categories; however, highest species richness and total abundances were observed at intermediate culvert densities and at natural reefs. Whereas the abundance of L. campechanus did not differ among density categories, mean total lengths of L. campechanus were greatest at the lower density. Our findings suggest that reefs should be deployed with intermediate patch density of 71–120 culverts in a 30-m radius to yield the highest fish abundances.     

Length–weight relation of the 14 fish species occurring on sandy beaches along a tropical river in the Amazon

We analyzed the length‐weight relation (LWRs) of 14 species of fish, sampled in 30 sandy beaches along the Acre river, encompassing approximately 300 km of the river between the municipalities of Brasileia and Rio Branco, Acre state, Brazil, during the draught period in 2017 (August and September). For sampling, we used a picaré type trawl with 9 m of length, 2 m of height and 5 mm mesh between opposing knots, during the day and night periods. New information was made available for eight fish species.     

Population Dynamics of the Pink Salmon Oncorhynchus gorbuschain the Basin of the Sea of Okhotsk in the 1990s

In the 1990s, an extensive body of data was gathered on the size of the Oncorhynchus gorbuschapink salmon populations of the Sea of Okhotsk at all the main developmental stages. A significant increase in numbers was found for juvenile pink salmon migrating into the offshore regions of the Sea of Okhotsk and the Pacific waters around the Kurils: from 250–450 million in 1990–1991 to 807–1570 million fish in 1993–1999. The overall number of migrating pink salmon in even years sharply increased in 1994 up to 215 million fish. After 1994, this estimate exceeded the number of migrating pink salmon in preceding odd years. Ocean survival of juvenile pink salmon gradually declined. This may be related to changes in the North Pacific pelagic ecosystems.     

Length–weight relationships for seven fish species of the Napo River,Upper Amazon,Peru

Length–weight relationships (LWR) were estimated for seven fish species from the Napo River and its main tributaries, Arabela and Curaray rivers, Amazon basin, Peru. A total of 652 specimens were sampled between 2012 and 2014 using seines and gillnets. This study reports new maximum total length for four species and new LWR and maximum total weight records for three and five species, respectively.     

Length–weight relationships of five fish species associated with krill fishery in the Atlantic sector of the Southern Ocean

Length–weight relationships (LWRs) of five fish species commonly associated with Antarctic krill fishery, were determined. Samples were collected with Chinese krill trawler (codend mesh size 2 cm) in the Atlantic sector of the Southern Ocean from January to August 2016. Data on LWRs and the relationships between weight and standard length as well as weight and total length of those species were updated for the database of FishBase. Those data on fish species derived from Antarctic krill fishery will be very helpful in understanding the interaction between krill fishery and the associated fish community.