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At least 19 recordsLinked to original sources
USGS2016

Aqueous exposure to the progestin, levonorgestrel, alters anal fin development and reproductive behavior in the eastern mosquitofish (Gambusia holbrooki)

Endogenous progestogens are important regulators of vertebrate reproduction. Synthetic progestins are components of human contraceptive and hormone replacement pharmaceuticals. Both progestogens and progestins enter the environment through a number of sources, and have been shown to cause profound effects on reproductive health in various aquatic vertebrates. Progestins are designed to bind human progesterone receptors, but they also have been shown to strongly activate androgen receptors in fish. Levonorgestrel (LNG) activates fish androgen receptors and induces development of male secondary sex characteristics in females of other species. Although behavior has been postulated to be a sensitive early indicator of exposure to certain environmental contaminants, no such research on the reproductive behavior of gestagen-exposed fish has been conducted to date. The goal of our study was to examine the exposure effects of a human contraceptive progestin, LNG, on the reproductive development and behavior of the viviparous eastern mosquitofish ( Gambusia holbrooki ). Internal fertilization is a requisite characteristic of viviparous species, and is enabled by an androgen driven elongation of the anal fin into the male gonopodium (i.e., phallus). In this study, we exposed adult mosquitofish to ethanol (EtOH control), 10 ng/L, and 100 ng/L LNG for 8 d using a static replacement exposure design. After 8 d, a subset of males and females from each treatment were examined for differences in the 4:6 anal fin ratio. In addition, paired social interaction trials were performed using individual control males and control females or females treated 10 ng/L or 100 ng/L LNG. Female mosquitofish exposed to LNG were masculinized as evidenced by the elongation of the anal fin rays, a feature normal to males and abnormal to females. LNG caused significant increases in the 4:6 anal fin ratios of female mosquitofish in both the 10 ng/L and 100 ng/L treatments, although these differences were not significant between the two treatments. LNG caused significant increases in the 4:6 anal fin ratio of males exposed to 100 ng/L, with no effects observed in the 10 ng/L treatment. In addition, the reproductive behavior of control males paired with female mosquitofish exposed to 100 ng/L LNG was also altered, for these males spent more time exhibiting no reproductive behavior, had decreased attending behavior, and a lower number of gonopodial thrusts compared to control males paired to control female mosquitofish. Given the rapid effects on both anal fin morphology and behavior observed in this study, the mosquitofish is an excellent sentinel species for the detection of exposure to LNG and likely other 19-nortestosterone derived contraceptive progestins in the environment.

General and Comparative Endocrinology↗
USGS2018

Evaluation of anal fin spines, otoliths, and scales for estimating age and back-calculated lengths of yellow perch in southern Green Bay

Southern Green Bay supports important fisheries for yellow perch Perca flavescens and valid estimates of age structure and growth are critical to effective management. Anal fin spines and scales are used by the Wisconsin Department of Natural Resources for age estimation, but these structures may provide lower precision and accuracy than otoliths. The primary objective of our assessment was to determine if age estimates, among-reader precision, and mean back-calculated total lengths (TLs) at age differed among scales, anal fin spines, and otoliths. Ages estimated from anal fin spines were more precise than scale ages, were as precise as otolith-based ages, and generally agreed with consensus ages estimated from sectioned otoliths. Relationships between TL and radii of calcified structures were linear for scales, anal spines, and otoliths along two different transects. Mean back-calculated TLs were generally similar between intercept-corrected direct proportion (ICDP) and linear regression (LR) models, but otolith-based direct proportion models (no intercept correction) generally provided higher back-calculated mean TLs at ages 1 and 2 than ICDP and LR models. Mean back-calculated TLs at age estimated from whole otoliths were higher than estimates for other structures; but differences among anal fin spines, scales, and sectioned otoliths were <10 mm. Our results suggest biologists have little to gain by switching to otoliths when assessing age structure and growth for this fast-growing yellow perch population with relatively few fish ≥age 6, but additional analyses are warranted for slower-growing perch populations in the Great Lakes where older fish are more common.

Wisconsin↗
USGS2017

Precision and accuracy of age estimates obtained from anal fin spines, dorsal fin spines, and sagittal otoliths for known-age largemouth bass

Sagittal otoliths are the preferred aging structure for Micropterus spp. (black basses) in North America because of the accurate and precise results produced. Typically, fisheries managers are hesitant to use lethal aging techniques (e.g., otoliths) to age rare species, trophy-size fish, or when sampling in small impoundments where populations are small. Therefore, we sought to evaluate the precision and accuracy of 2 non-lethal aging structures (i.e., anal fin spines, dorsal fin spines) in comparison to that of sagittal otoliths from known-age Micropterus salmoides (Largemouth Bass; n = 87) collected from the Ocmulgee Public Fishing Area, GA. Sagittal otoliths exhibited the highest concordance with true ages of all structures evaluated (coefficient of variation = 1.2; percent agreement = 91.9). Similarly, the low coefficient of variation (0.0) and high between-reader agreement (100%) indicate that age estimates obtained from sagittal otoliths were the most precise. Relatively high agreement between readers for anal fin spines (84%) and dorsal fin spines (81%) suggested the structures were relatively precise. However, age estimates from anal fin spines and dorsal fin spines exhibited low concordance with true ages. Although use of sagittal otoliths is a lethal technique, this method will likely remain the standard for aging Largemouth Bass and other similar black bass species.

Southeastern Naturalist↗
USGS2023

First investigations on lamprey responses to elevated total dissolved gas exposure and risk of gas bubble trauma

A flexible spill program in the federal Columbia River power system increased the total dissolved gas (TDG) water quality standards (i.e., the gas cap) from 120% to 125%. Spill is used to pass juvenile salmon (Oncorhynchus spp.) over dams, but it can generate elevated TDG, and exposed fish can develop gas bubble trauma (GBT) or experience mortality. Juvenile salmon are monitored for GBT through the Fish Passage Center’s (FPC), and under the flexible spill program, native non-salmonid fishes are also monitored. Pacific Lamprey (Entosphenus tridentatus) are exposed to elevated TDG, but nothing is known about their risk for GBT. This project is the first to evaluate GBT in lamprey, beginning with larval and juvenile lamprey in a controlled laboratory setting. These early life stages were chosen for this initial work because they have been shown to be more sensitive to GBT in other fish species. We modified the FPC protocol for GBT exams to be specific to lamprey and ranked bubbles in the mouth, eyes (juveniles only), gill pores, first and second dorsal fins, caudal fin, anal fin, vent, and body. We followed the FPC ranking criteria and assigned rank based on the proportion of the area occluded with bubbles, as 0=no bubbles, 1=1-5%, 2=6-25%, 3=26-50%, and 4=>50%. Four experiments were completed with larval lamprey from January to September 2022 using small (70 mm total length or less) and large (86 mm total length or greater) larvae in approximately equal proportions. Experiments included: (1) 130% TDG for 31 d, (2) 125% TDG for 91 d, (3) 130% TDG for 20 d with assessments of burrowing performance, and (4) 128-138% TDG for 3-4 d with assessments of predator avoidance ability and the corresponding untreated control groups. The first and second experiments had similar study designs and findings. First, we tested an acute exposure at 130% TDG and then we tested a chronic exposure at 125%, to represent a full spill season. None of the controls (exposed to normally saturated water) experienced mortality or showed GBT signs. Few lamprey in the treatment groups (5% in Experiment 1; 0% in Experiment 2) showed GBT signs, and there were no mortalities (n=200 fish experiment 1; n=100 fish Experiment 2). Lamprey with GBT signs had bubbles on the body, with low severity ranks. During external exams for Experiment 2, we observed bubbles in the gut of several lamprey. The light coloration and transparency of the body made these observations possible, and we confirmed the finding with internal exams. From day 9 to day 91, 70.8% of the lamprey examined had bubbles in the gut. We observed five lamprey that were positively buoyant in the test tanks, and we likely underestimated the prevalence of floating as our procedures were not initially designed to document this sign. In our third experiment, burrowing performance was not significantly different between lamprey exposed to 130% TDG and controls. Mortality was 4.2% in the treatment group, but no GBT signs were observed. The proportion of lamprey with positive buoyancy increased through time, with 87.5% of fish floating on day 20 (end of the test). Bubbles in the gut were observed for some lamprey on each of five sampling dates (day 2 to 20), with prevalence ranging from 50-100%. Median burrow times ranged from 28 to 154 sec for treatment fish and from 40 to 100 sec for controls. We noted some atypical behaviors during burrow performance tests, including lamprey that were positively buoyant and unable to descend through 0.5 m of water to reach the sediment as well as lamprey that were unable to complete burrowing (within 10 min test period). These lamprey were so buoyant that they repeatedly floated to the surface of the water when they stopped or slowed their burrowing movements. Predator avoidance ability was assessed in our fourth experiment by exposing lamprey with GBT signs (floating) and controls to sculpin (Cottus spp.) until about 50% of the fish had been consumed or 2 h had passed. We completed five predation trials, testing the hypothesis that an equal proportion of treatment and control lamprey would be consumed. Treatment groups were generated by exposing 15 lamprey to 128-138% TDG for 3-4 d, until at least 10 lamprey were floating. Overall, 41 treatment and 46 control fish were eaten and there was no evidence that sculpin preferentially preyed upon lamprey with GBT signs. Additional tests with another predator are recommended. Two experiments were completed with juvenile lamprey from March to November 2022: Experiment 5 exposed fish to 125% TDG for 10 d and Experiment 6 exposed fish to 125% for 16 d. Mortality rates for the treatment groups were 21.7% and 20.0% for these experiments, respectively, and few lamprey (4 per experiment) showed GBT signs. With the results from experiments pooled, bubbles were observed in all body areas with low severity ranks (means 0-1). We observed some exophthalmia and bubbles behind the gill pores, in addition to bubbles in the gut and fish floating. The presence of bubbles in or near the gill pores was the likely cause of death as exam findings included enlarged gill pore areas and restricted openings. This project provided the first insights into lamprey responses to elevated TDG, but substantial learning opportunities remain. Our findings highlight that lamprey are vulnerable to GBT, but the effects are generally sublethal and would not be detected using FPC exam procedures. For example, we observed larval and juvenile lamprey that had bubbles in the gut and/or were floating, although these conditions were not consistently linked. More data are needed, but we surmise that it takes some time for bubbles to form in sufficient quantity to create the floatation required to overcome the mass of the lamprey. Positive buoyancy in natural settings could have substantial impacts to the risk of mortality for lamprey. Future studies could test GBT risk for larval lamprey in burrows, investigate the influence of lamprey size, measure performance (e.g., burrowing, swimming, predator avoidance ability) after elevated TDG exposure, and describe the rate that GBT signs dissipate when lamprey are returned to normally saturated water.

Report↗
USGS2003

Fin development in stream- and hatchery-reared Atlantic salmon

To determine the effect of development and environment on fin growth, we measured fin lengths of juvenile Atlantic salmon (Salmo salar) from two hatcheries (August, October and April-May), stream-reared fish (July and October) stocked as fry into two tributaries, and smelts from the main stem of the Connecticut River (May). For stream-reared parr, there was a linear relationship between the dorsal, caudal and anal fins with fork length, while the pectoral, pelvic and adipose fins exhibited a curvilinear relationship with fork length. Parr from a high gradient stream had larger caudal fins than fish from a low gradient stream, but other fins did not differ. Regression lines for the fins of stream-reared smelts were all linear when fin length was regressed against fork length. Stream-reared parr had larger pectoral, pelvic and anal fins than smolts of similar size while dorsal and caudal fin lengths did not differ. Regression equations formulated using the fins of stream-reared parr were used to calculate the percent difference (100 x observed fin length/expected) in fin lengths between stream- and hatchery-reared parr. The pelvic, adipose, caudal and anal fins of hatchery-reared parr showed no signs of degeneration by the first sampling period 7 months after hatching, whereas degeneration in the pectoral (13-20%) and dorsal (15-18%) fins was evident at this time. By the end of the study, degeneration was present in every fin except the adipose, with the pectoral (35-65%) and dorsal (32-58%) fins exhibiting the greatest amount of fin loss. All fins of hatchery-reared parr became shorter with time. There were minor differences in fin degeneration among parr from the two hatcheries, but the overall pattern of decreasing fin size was similar, indicating a common cause of fin degeneration. Comparison of stream- and hatchery-reared fish is a valuable means of determining the impact of captive environments on fin growth.

Aquaculture↗
USGS2007

Review of the crevalle jacks, Caranx hippos complex (Teleostei: Carangidae), with a description of a new species from West Africa

The Caranx hippos species complex comprises three extant species: crevalle jack (Caranx hippos) (Linnaeus, 1766) from both the western and eastern Atlantic oceans; Pacific crevalle jack (Caranx caninus) Gu??nther, 1868 from the eastern Pacific Ocean; and longfin crevalle jack (Caranx fischeri) new species, from the eastern Atlantic, including the Mediterranean Sea and Ascension Island. Adults of all three species are superficially similar with a black blotch on the lower half of the pectoral fin, a black spot on the upper margin of opercle, one or two pairs of enlarged symphyseal canines on the lower jaw, and a similar pattern of breast squamation. Each species has a different pattern of hyperostotic bone development and anal-fin color. The two sympatric eastern Atlantic species also differ from each other in number of dorsal- and anal-fin rays, and in large adults of C. fischeri the lobes of these fins are longer and the body is deeper. Caranx hippos from opposite sides of the Atlantic are virtually indistinguishable externally but differ consistently in the expression of hyperostosis of the first dorsal-fin pterygiophore. The fossil species Caranx carangopsis Steindachner 1859 appears to have been based on composite material of Trachurus sp. and a fourth species of the Caranx hippos complex. Patterns of hyperostotic bone development are compared in the nine (of 15 total) species of Caranx sensu stricto that exhibit hyperostosis.

Fishery Bulletin↗
USGS2020

Comparison of specimen- and image-based morphometrics in Cisco

Morphometric data from fish are typically generated using one of two methods: direct measurements made on a specimen or extraction of distances from a digital picture. We compared data on 12 morphometrics collected with these two methods on the same collection of Cisco Coregonus artedi from Lake Ontario, North America, to assess the degree of bias in measurements made directly on a specimen- vs. an image-based method. We also assessed the degree of reproducibility within the image-based method by evaluating the amount of variation between different analysts for each morphometric method. Our results indicate specific morphometrics may be more prone to bias across the two methods and between analysts. Four of 12 morphometrics evaluated showed significant deviation from a 1:1 relationship that would be expected if the imaged-based method produced accurate specimen-based measurements. Pelvic fin length and pelvic–anal fin distance had the highest between-analyst variation for image-based landmarks, indicating low reproducibility for these metrics, compared with pectoral fin or total length, which had lower between-analyst variation. Although some morphometric measurements can be accurately obtained with either method, and therefore potentially used interchangeably in studies on Cisco morphology, our findings highlight the importance of considering method bias in morphometric studies that use data collected by different methods.

Journal of Fish and Wildlife Management↗
USGS2004

Natural hybrids of the madtoms, Noturus flavus and Noturus insignis, from the Monongahela River drainage, West Virginia

Natural hybridization is rare in the family Ictaluridae. Putative hybrids of the madtoms Noturus flavus and N. insignis were collected from Blackwater River, Monongahela River drainage, WV. Noturus flavus is native to the Monongahela River drainage, whereas N. insignis is nonnative. We quantified morphological differences among N. flavus, N. insignis, and putative hybrids by sheared principal components analysis of morphometric characters. Putative hybrids were intermediate in tooth patch dimensions, caudal fin pigmentation, length of the dorsal fin base, distance between the adipose/caudal notch and base of caudal fin, and position of anal fin. Hybridization between N. flavus and N. insignis is supported by morphological intermediacy, and may be linked to higher abundances of N. insignis or degraded habitat in the Blackwater River.

Northeastern Naturalist↗
USGS2022

Occurrence of a reproducing wild population of Channa aurolineata (Pisces: Channidae) in the Manatee River drainage, Florida

We report on the discovery of a wild, reproducing population of Channa aurolineata (Pisces: Channidae) in west-central Florida (USA), and first documented occurrence of snakeheads in the Gulf Coast region. Channa aurolineata is a large, predatory fish of the bullseye snakehead “Marulius group” species complex from Asia. Adult and juvenile specimens were captured in June 2020 in a 1.8-hectare pond that connects during high water to a small stream within the Manatee River-Tampa Bay Basin. The pond site is 250-km from the only other wild C. aurolineata population in the USA (present in southeast Florida since ca. 2000) and is considered a separate introduction and not the result of natural dispersal. Morphological and molecular comparisons revealed high overlap between the two Florida populations, evidence humans may have transported fish between sites. To verify identification, we compared Florida samples to C. aurolineata from Thailand and found mtDNA-COI barcode sequences to be identical or to differ by only a single base pair. Life body coloration of Florida samples matched their Asian counterparts, but Florida specimens averaged fewer dorsal fin rays (53.6 vs. 56.0), anal fin rays (34.2 vs 36.1), lateral line scales (65.3 vs. 67.4), and vertebrae (62.1 vs. 64.3), differences implying possible founder effect or sampling bias. Existence of this invasive predator is a concern because of the risk of spread and negative ecological effects, including an observation of terrestrial hunting behavior. In 2020–2021, several hundred C. aurolineata were removed from the pond by nets and electrofishing, and surveys suggested the population had not spread to nearby waters. In May 2021 the pond was treated with rotenone and 48 more specimens were recovered. No additional snakeheads have been sighted since the piscicide operation, although verification of eradication will require monitoring of the watershed.

Florida↗
USGS1970

Fin degeneration of young-of-the-year Alosa pseudoharengus (Clupeidae) in southern Lake Michigan

Young-of-the-year alewives, Alosa pseudoharengus, with extremely shortened caudal fins were observed at four locations in southern Lake Michigan between 1964 and 1968. Some of the fins appeared stunted or underdeveloped, but microscopic examination revealed a deterioration of the fins and not an ontogenetic abnormality. Deterioration of the caudal fin was frequently accompanied by degeneration of the dorsal and anal fins. Degenerate fins were not found on other species nor on older alewives, with the exception of one known yearling alewife at Waukegan and possibly a few of the larger fish at Milwaukee.

Copeia↗
USGS2006

Morphology of androgenetic and gynogenetic grass carp, Ctenopharyngodon idella (Valenciennes)

Crosses between female carp x male grass carp resulted in androgenetic grass carp and hybrids. Fertilizing grass carp eggs with carp milt that had been irradiated with ultraviolet light for 15 min at 1.0 mW/cm 2 produced gynogenetic grass carp. We compared the morphology of experimental progeny with that of the parental species to determine if inheritance was strictly matroclinous in gynogenesis and strictly patroclinous in andro-genesis. Dorsal and anal fin rays, lateral line scales, gill rakers, pharyngeal teeth, and the relative length of the dorsal fin all suggested that gynogenetic grass carp were identical with the maternal species and androgenetic grass carp with the paternal species. Hybrids were intermediate between the parents except that the number of anal rays was identical with that in carp. The number of dorsal rays, the body depth, and the pharyngeal teeth in hybrids were more like those in carp than in grass carp, whereas the number of gill rakers was more similar to that in the paternal species.

Journal of Fish Biology↗
USGS2005

Stock structure of Lake Baikal omul as determined by whole-body morphology

In Lake Baikal, three morphotypes of omul Coregonus autumnalis migratorius are recognized; the littoral, pelagic, and deep-water forms. Morphotype assignment is difficult, and similar to that encountered in pelagic and deep-water coregonines in the Laurentian Great Lakes. Principal component analysis revealed separation of all three morphotypes based on caudal peduncle length and depth, length and depth of the body between the dorsal and anal fin, and distance between the pectoral and the pelvic fins. Strong negative loadings were associated with head measurements. Omul of the same morphotype captured at different locations were classified to location of capture using step-wise discriminant function analysis. Jackknife correct classifications ranged from 43 to 78% for littoral omul from five locations, and 45&ndash;86% for pelagic omul from four locations. Patterns of location misclassification of littoral omul suggested that the sub-population structure, hence stock affinity, may be influenced by movements and intermixing of individuals among areas that are joined bathymetrically. Pelagic omul were more distinguishable by site and may support a previous hypothesis of a spawning-based rather than a foraging-based sub-population structure. Omul morphotypes may reflect adaptations to both ecological and local environmental conditions, and may have a genetic basis.

Journal of Fish Biology↗
USGS2017

A new species of freshwater eel-tailed catfish of the genus Tandanus (Teleostei: Plotosidae) from coastal rivers of mid-northern New South Wales, Australia

Tandanus bellingerensis , new species, is described based on specimens from four river drainages (Bellinger, Macleay, Hastings, and Manning rivers) of the mid-northern coast of New South Wales, Australia. Previously, three species were recognized in the genus Tandanus : T. tropicanus of the wet tropics region of northeast Queensland, T. tandanus of the Murray-Darling drainage and coastal streams of central-southern Queensland and New South Wales, and T. bostocki of southwestern Western Australia. The new species is distinguished from all congeners by a combination of the following morphologic characters: a high count of rays in the continuous caudodorsal and anal fins (range 153–169, mode 159), a high count of gill rakers on the first arch (range 35–39, mode 36), and strongly recurved posterior serrae of the pectoral-fin spine. Additionally, results from previously conducted genetic studies corroborate morphologic and taxonomic distinctness of the new species.

New South Wales↗
USGS2020

Identification of Acara (Cichlidae: Cichlasoma) established in Florida, USA

The Black Acara, Cichlasoma bimaculatum (Linnaeus, 1758), was first reported as introduced to Florida in 1965. Native to Venezuela, Guyana, Suriname, western French Guiana, and northern Brazil, the species is now distributed throughout Florida’s southern peninsula. Examination of live and preserved acara from Central Florida, heretofore identified as Black Acara, reveal the presence of an additional acara species, the Chanchita, Cichlasoma dimerus (Heckel, 1840). The Chanchita is native to Bolivia, Paraguay, Uruguay, southern Brazil, and northeastern Argentina. Despite similarities, Black Acara and Chanchita can be distinguished by number of anal-fin spines, body and fin color, caudal-fin pattern, and head, nape, and upper-flank scale-rim pigment. The Chanchita is established in multiple Central Florida drainages with the earliest known record from July 27, 2000. The Chanchita has not been found to co-occur with the Black Acara. The presence of Chanchita in more than one Central Florida spring and the widespread distribution of this previously unreported introduced species may be of concern to natural resource managers.

Florida↗
USGS2020

Beloniformes: Belonidae (Needlefishes) and Hemiramphidae (Halfbeaks)

The order Beloniformes (or Synentognathi) contains two suborders, six families, 37 genera, and about 235 species of atherinomorph fishes (Rosen & Parenti 1981; Collette et al. 1984; Collette 2004). Features common to these fishes include dorsal and anal fins on the rear half of the body, abdominal pelvic fins with six soft rays, no fin spines, lateral line running along the ventral edge of the body, an open nasal pit, and lower pharyngeal bones fused into a triangular plate (leading to the name Synentognathi). Two families, the Flying fishes (Exocoetidae) and the Sauries (Scomberesocidae) are restricted to marine waters but several genera of Needlefishes (Belonidae) and Halfbeaks (Hemiramphidae and Zenarchopteridae) are restricted to fresh waters and other genera contain estuarine, freshwater, and marine species. The family name Belonidae, based on the type genus Belone, means needle in reference to the unusually long and slender jaws of most Needlefishes. Similarly, the family name Hemiramphidae means half-beak, alluding to the conspicuous presence of a long slender lower jar and a short upper jaw in most species. Two species of Needlefishes (Belonidae, Strongylura) and two species of Halfbeaks (Hemiramphidae, Hyporhamphus) occur in North American fresh waters.

Book chapter↗
USGS2020

Validity of age estimates from muskellunge (Esox masquinongy) fin rays and associated effects on estimates of growth

Accurate age estimates are critical for understanding life histories of fishes and developing management strategies for fish populations. However, validation of age estimates requires known-age fish, which are often lacking. We used known-age (ages 1–25) muskellunge ( Esox masquinongy ) to determine the precision and accuracy of age estimates from fin rays. We also determined whether fin location (anal or pelvic), fin ray number, and preparation methods affected accuracy and precision. Lastly, we determined whether von Bertalanffy growth parameters estimated from fin ray ages were similar to parameters estimated from known ages. Precision and accuracy of age estimates from anal and pelvic rays were similar and estimates were relatively precise (coefficient of variation = 8.5%) and accurate (mean absolute difference from known age = 0.85 years) for ages 4–15, but ages were overestimated for younger fish and underestimated for older fish. Growth models based on estimated age were similar to models based on known age. Anal and pelvic rays offer a nonlethal alternative for age estimation of muskellunge ages 4–15 and for producing reliable estimates of growth.

Illinois, Iowa, Kentucky, Virginia, Wisconsin↗
USGS2017

Comparison of the precision of age estimates generated from fin rays, scales, and otoliths of Blue Sucker

Evaluating the precision of age estimates generated by different readers and different calcified structures is an important part of generating reliable estimations of growth, recruitment, and mortality for fish populations. Understanding the potential loss of precision associated with using structures harvested without sacrificing individuals, such as scales or fin rays, is particularly important when working with imperiled species, such as Cycleptus elongatus (Blue Sucker). We collected otoliths (lapilli), scales, and the first fin rays of the dorsal, anal, pelvic, and pectoral fins of 9 Blue Suckers. We generated age estimates from each structure by both experienced ( n = 5) and novice ( n = 4) readers. We found that, independent of the structure used to generate the age estimates, the mean coefficient of variation (CV) of experienced readers was approximately 29% lower than that of novice readers. Further, the mean CV of age estimates generated from pectoral-fin rays, pelvic-fin rays, and scales were statistically indistinguishable and less than those of dorsal-fin rays, anal-fin rays, and otoliths. Anal-, dorsal-, and pelvic-fin rays and scales underestimated age compared to otoliths, but age estimates from pectoral-fin rays were comparable to those from otoliths. Skill level, structure, and fish total-length influenced reader precision between subsequent reads of the same aging structure from a particular fish. Using structures that can be harvested non-lethally to estimate the age of Blue Sucker can provide reliable and reproducible results, similar to those that would be expected from using otoliths. Therefore, we recommend the use of pectoral-fin rays as a non-lethal method to obtain age estimates for Blue Suckers.

Louisiana, Texas↗
USGS2023

Precision of structures used to estimate age and growth of Apache Trout from Arizona

Obtaining reliable information on the age structure of fish populations is important for making conservation and management decisions. We sought to evaluate precision and reader confidence in age estimates from scales (two body locations), sectioned fin rays (pectoral, pelvic, anal), and sectioned sagittal otoliths from Apache Trout Oncorhynchus apache ( n = 78 fish) sampled from the East Fork White River, Arizona, in 2017. Two experienced readers without prior knowledge of fish length aged structures independently. Each reader provided a confidence rating of 0 (no confidence) to 3 (completely confident) as a measure of readability. Both readers were unable to estimate age from scales collected from the area just posterior to the insertion of the pectoral fin. We used scales removed from an area just dorsal to the lateral line and posterior to the dorsal fin in all analyses. Percentage of exact agreement between readers was highest for scales and otoliths (>72.0%) and lowest for fin rays (31.8–58.1%). Average confidence rating was highest for sectioned otoliths (mean ± SE, 2.1 ± 0.07), and lowest for anal fin rays (0.3 ± 0.06) and scales (0.7 ± 0.05). We compared consensus ages from otoliths to the other structures. Percentage of exact agreement with otolith age was low and varied from 21.6 to 35.7% among structures. Similarly, percentage of agreement within 1 y was also low among structures (58.0–70.2%). Scales consistently underestimated age of age-4 and older fish (based on otolith age), whereas fin rays tended to overestimate age of younger fish and underestimate age of older Apache Trout. Although sectioned otoliths require lethal sampling, they produced the most precise age estimates for Apache Trout with the highest reader confidence. Dorsal scales may be a suitable nonlethal alternative to otoliths if ages for only young fish (age 3 and younger) meet study objectives.

Arizona↗