Otolith Sections Research Articles

Otolith chemistry reveals painted notie (Nototheniops larseni) juvenile stocks differed between southern Bransfield Strait and South Georgia shelf

The painted notie Nototheniops larseni is a link between the lower and upper levels of food web as one of the most abundant and widespread fish species in the Southern Ocean. Otolith chemistry is a well-established approach for studying fish life histories and differentiating stock structure, and chemical analysis of otolith core can be used to distinguish fish stocks. This study demonstrates that the N. larseni juvenile stocks in the southern Bransfield Strait are sourced from the same environment, but the stocks in the southern Bransfield Strait and at South Georgia shelf are separated geographically using chemical data from otolith core, hatching and feeding checks, and edge. The ratios of 7Li to 42Ca across otolith sections of N. larseni juveniles in the southern Bransfield Strait are lower significantly than those at the South Georgia shelf, indicating the Li in fish otolith may act as a chemical tag for reflecting sea ice dynamics in the Southern Ocean.

A Preliminary Study of the Age and Growth Patterns of a Sea Toad, Chaunax abei Le Danois, 1978, in Suruga Bay, Japan

Chaunax abei Le Danois, 1978, is a bottom-dwelling species caught by bottom trawls in Suruga Bay. In the present study, we assessed the age and growth pattern of C. abei from Suruga Bay during the period of 2021–2022 for the first time. The total length (TL) of the population ranged from 37.4–268.8 mm (mean ± SD: 124.7 ± 3.64 mm), and the fish weight (W) between 1.11–491.75 g (mean ± SD: 58.40 ± 7.25 g). The length-weight relationship was estimated as 𝑊𝑊=(2.07 × 10−5)𝑇𝑇𝑇𝑇2.996 (r2 = 0.937). Age determination was based on annual growth ring counts of transverse sections of the sagittal otoliths and age ranged from 1 to 12 years, with the majority of fish aged 4 (32.79 %) years old. The von Bertalanffy growth function was used to model the growth, and the parameters were found as: TL∞ = 468.1 mm, K = 0.056 year-1, t0 = -0.402 year. This research provides the first results on the growth of C. abei and enriches the regional fisheries biology database. Furthermore, it presents the primary population data on the growth patterns of one of the chaunacid species.

Age validation of yellowfin and bigeye tuna using post-peak bomb radiocarbon dating confirms long lifespans in the western and central Pacific Ocean

Abstract Age-reading protocols for tuna species using annual growth zones in thin-cut transverse otolith sections have produced greater age estimates than previous methods. Lifespan estimates for yellowfin (YFT) and bigeye (BET) tuna (Thunnus albacares and T. obesus) were validated up to 16–18 years in the western North Atlantic Ocean using bomb 14C dating and the current study extends the approach to YFT and BET of the western and central Pacific Ocean (WCPO). Archived otoliths from young-of-the-year (YOY) tuna caught in the WCPO were analysed for 14C to establish a reference chronology covering 30 years (1989–2019). This YOY 14C time series exhibited strong concordance with existing coral-otolith 14C references for the tropical-subtropical Pacific Ocean and was combined as a single chronology. Otolith cores from YFT aged 1–14 years and BET aged 1–13 years from presumed annual counts were analysed for 14C. These measurements aligned with the reference chronology for the calculated hatch years for both species. These findings provide strong evidence that growth zones in thin-sectioned otoliths are deposited annually for YFT and BET of the WCPO and that age interpretation is correct using the current age reading protocol with little to no bias.

Evaluation of Age Estimates and Resulting Population Metrics Using Four Aging Methods from a Midwestern Blue Catfish Population

Abstract Lapillus otoliths and several preparations of pectoral fin spines have been used to age Blue Catfish Ictalurus furcatus; however, there are limited studies examining relative precision of age estimates. Further, comparisons of population characteristics (e.g., growth, mortality) resulting from age structure evaluations are needed to help fisheries managers balance resources needed to conduct investigations with quality of subsequent data. We examined sectioned Blue Catfish lapillus otoliths and sectioned pectoral spine articulating processes, basal recesses, and articulating surfaces to compare relative precision of age estimates. Additionally, dynamic rate functions and resulting population models were examined to determine if variation in age estimates resulted in divergent interpretation of population characteristics. Generally, aging precision was greatest for articulating surface and lapillus otolith sections. Although growth models generated from each aging structured differed, mortality estimates and conclusions drawn from harvest-regulated population modeling were similar across structures. These results demonstrate that although there is variability in precision and growth modeling among different Blue Catfish aging structures, estimates for key population parameters remain consistent.

Puzzling parrotfishes: Radiocarbon age validation and updated longevity estimates for western Atlantic species in support of sustainable fisheries management

For management efforts to succeed in Caribbean fisheries, local fishers must support and be willing to comply with fishing regulations. This is more likely when fishers are included in a stock assessment process that utilizes robust scientific evidence, collected in collaboration with fishers, to evaluate the health of fish stocks. Caribbean parrotfishes are important contributors to coral reef ecosystem health while also contributing to local fisheries. Scientifically robust stock assessments require regional species-specific information on age-based key life history parameters, derived from fish age estimates. Evaluation of the accuracy of age estimation methods for fish species is a critical initial step in managing species for long-term sustainable harvest. The current study resulted from a collaborative research program between fish biologists and local fishers investigating age, growth, and reproductive biology of the seven parrotfish species landed in U.S. Caribbean fisheries; specifically, we validated age estimation for stoplight parrotfish Sparisoma viride and queen parrotfish Scarus vetula. This is the first study to directly validate age estimation for any parrotfish species through analysis of Δ14C from eye lens cores. Our age estimation validation results show that enumeration of opaque zones from thin sections of sagittal otoliths for a Sparisoma and a Scarus species provides accurate age estimates. The oldest stoplight parrotfish and queen parrotfish in the Δ14C age estimation validation series were 14 y and 16 y; while the oldest stoplight parrotfish and queen parrotfish we aged to-date using the Δ14C validated age estimation method were 20 y and 21 y, respectively. Fish longevity (maximum age attained/life span) is a key life history parameter used for estimation of natural mortality, survivorship, and lifetime reproductive output. Past reviews on parrotfishes from the Pacific and Atlantic concluded that most Caribbean/western Atlantic parrotfish species are relatively short-lived with estimated maximum ages ranging from 3–9 y. However, information from our collaborative research in the U.S. Caribbean combined with recently published age estimates for Brazilian parrotfish species indicate that many western Atlantic parrotfishes are relatively long-lived with several species attaining maximum ages in excess of 20 y.

Age interpretation of cod otoliths using deep learning

Fish age estimation plays a crucial role in stock management and provides valuable information for biological studies. Fish age is typically estimated by experts that manually count annual increments in otoliths. This process is prone to age reader bias, which makes comparisons between readers and labs challenging, and requires considerable time and resources. In this study, we developed a machine learning framework for fish age prediction using 5150 images of otoliths from Barents Sea Atlantic cod (Gadus morhua) collected between 2012 and 2018. In contrast to previous studies that utilise models trained on otolith sections, we used images of broken otoliths that require no processing prior to imaging, and hence, could potentially facilitate at-sea age estimation. We trained convolutional neural networks (CNNs) based on two modern architectures (EfficientNetV1 and EfficientNetV2), which vary in model size (number of model parameters), and compared performance. Model average accuracy was 72.7% and mean-squared-error was 0.284 when compared with the human-read ages. The models' accuracy for one- and two-year-old individuals was over 90% and no systematic bias in the age predictions across age groups was detected. The best models were EfficientNet B4 and EfficientNet B6 using images taken with low exposure times. A maximum accuracy of 78.6% was achieved using an ensemble consisting of six models. Model predictions were also strongly correlated, limiting the utility of building large ensembles Model performance was compared to the results of an internal workshop where 100 independent images of broken otoliths were aged by a group of experts. Variations in percentage agreement between age classes showed a similar pattern (decreasing with age) in both CNN-based predictions and age estimates made by the expert group. While CNN-based percentage agreement was often lower than the expert estimates, it remained within or close to the range of percentage agreement observed across all readers. Our results demonstrate the potential of deep learning techniques for extracting age estimates from otolith images. When developing frameworks for age estimation using machine learning, we recommend EfficientNet B4 models are used as they are quicker to train than larger models and perform well. Ensemble approaches are also recommended if sufficient computational resources are available, as they can provide increased accuracy and lower variance of the predictions.

Age estimates derived from hard parts of swordfish Xiphias gladius from the north-western Mediterranean Sea.

Accurate age estimates for fish are critical for properly understanding stock dynamics and health; this is particularly true for larger billfishes. Here we determined the most accurate aging estimation methods for swordfish (Xiphias gladius). We compared age estimates obtained from fin-ray sections, otolith sections, whole otoliths, and vertebrae collected from 87 swordfish off the east coast of Corsica. Age estimates from otolith sections were most consistently estimated across different readers (lowest average percentage error), followed by fin-ray sections, third vertebrae, and whole otoliths. When the age estimates from the otolith sections were compared with the other three age sclerochronological methods, we found the average percentage error to be lowest between the otolith section and fin-ray methods. However, age estimates from fin rays proved most useful for estimating swordfish younger than 6 years, as the fin ray-based age diverged from that of the otolith sections as the swordfish aged. Combining fin ray and otolith section techniques, we estimated the growth parameters of 1-12-year-old females (L∞ = 259.412, k = 0.113, t0 = -2.499) and 1-7-year-old males (L∞ = 175.543, k = 0.202, t0 = -2.239). We found that females grew significantly faster than males after 3 years and remained larger thereafter. Our calculated growth rates for this region of the north-western Mediterranean Sea were lower than those of the Atlantic, Pacific, and eastern Mediterranean Sea swordfish populations, and similar to growth rates recorded for the western Mediterranean Sea populations. Our study provides critical knowledge on biological-related parameters to serve as a guide for preserving the swordfish population in the Mediterranean Sea.

Validation of annual growth zone formation in gray triggerfish Balistes capriscus dorsal spines, vertebrae, and otoliths

Uncertainty in age estimates from dorsal spines has been a persistent issue in stock assessments of gray triggerfish, Balistes capriscus. This study sought to validate the annual deposition of growth zones on dorsal spines, vertebrae, and otoliths of gray triggerfish through chemical marking. Fish (n = 101) were collected from offshore habitats and held in an aquaculture facility. 74 adult fish were chemically marked with a 50 mg/kg body weight injection of calcein, and reared for an average of 527 days post-marking. At intervals, fish were sacrificed and first dorsal spines, vertebrae, and otoliths were extracted and sectioned. Annuli, were enumerated for spines (n = 96), vertebrae (n = 94), and otoliths (n = 48) and ranged from 0 to 11 annuli for spines and vertebrae, and 1–12 annuli for otoliths. Age bias plots showed strong agreement between spine and vertebra annuli counts for all observed ages, while counts from spines and vertebrae appeared to underage beginning at age 5 when compared to otolith annuli counts. Tests of symmetry indicated that the annuli counts between paired age structures were not biased (p > 0.05). Analysis of growth zones observed distal to calcein marks in all of the age structures confirmed that these zones were deposited annually, and the expected number of these zones, or annuli, were observed in 91% of spine, 90% of vertebrae, and 100% of otolith sections. Marginal increment analysis of ageing structures indicated that annuli form during summer months. Percentages of annuli deposited on the margins peaked in June for spines (58%) and otoliths (29%), and August for vertebrae (30%). Results from this study validate the annual deposition of growth zones but further consideration needs to be taken when ageing older than age-4.

Bomb radiocarbon dating reveals 40‐year lifespan of Shovelnose Sturgeon (Scaphirhynchus platorynchus)—Implications for stock assessments of long‐lived, primitive fishes

AbstractStock assessments for Shovelnose Sturgeon have largely been limited to age and growth analyses using pectoral fin rays despite potential underestimation of age and lack of age validation. Fisheries stock assessments rely on accurate estimates of vital rates for effective fisheries management, within which fish age and lifespan are of primary importance. Age was estimated using pectoral fin rays and otolith sections, and bomb radiocarbon (14C) dating was applied to otolith cores to determine lifespan and validate ages. Age reading of fin rays was straightforward, whereas most otolith thin sections provided two age‐reading scenarios: lumping (primary increments) or splitting (finer increments) presumed annuli. While fin‐ray estimates led to a maximum age of 14 years, otolith estimates led to maximum ages of 27 and 42 years.14C dating provided support for a combination of lumping early in life, to splitting in later years, and validation of a ~40‐year lifespan. Age reading of otoliths was imprecise and resulted in ~40% of thin sections that were not age scoreable. However, scoreable otolith sections, coupled with14C dating, resulted in growth and lifespan information that are the most accurate to date for Shovelnose Sturgeon and can be used as a baseline toward stock assessment refinements.

Life history and stock synthesis assessment of Prionotus punctatus (Teleostei, Triglidae) in southern Brazil

AbstractAge, growth, and maturity of the bluewing searobin Prionotus punctatus were studied to assess its stock status in southern Brazil. Total length compositions, weight, sex, and maturity stage were recorded from commercial landings, and ages were estimated from transverse sections of the sagittal otolith. The oldest observed specimen was a 12‐year‐old female. Females grew to a larger asymptotic length (L∞ = 384.4 mm) than males (L∞ = 311.7 mm) but at a slower instantaneous rate (kfemales = 0.41 year−1, kmales = 0.75 year−1). Reproduction occurred from spring to early fall. Females size‐ and age‐at‐maturity was estimated at 246.8 mm and 1.66 years, while males were at 237.2 mm and 1.38 years. Based on a statistical catch‐at‐age stock assessment, the spawning biomass declined 84% from 1976 to 2000 being classified as overfished and suffering from overfishing (B/Bmsy = 0.62; F/Fmsy >1). P. punctatus was regularly discarded by industrial fisheries before 2000 but suffered from high exploitation in the last decades. These results highlight the need for the species to be included in Brazil's fishery management plans.

Preliminary sagitta otolith sections of some small-scale fishery species in the Colombian Pacific Ocean

Preliminary sagitta otolith sections of some small-scale fishery species in the Colombian Pacific Ocean

Age and growth of the red flounder Paralichthys orbignyanus (Teleostei: Pleuronectiformes) in southern Brazil

The red flounder Paralichthys orbignyanus is a large pleuronectiform fish endemic in coastal waters, coastal lagoons and estuaries in the southwestern Atlantic. Although less abundant than other Paralichthys spp, its high price makes it a valuable resource for small-scale fishers that have been intensely fished in the last decades. To study its growth and lifespan in southern Brazil, we examined thin otolith sections collected for age determinations of both young-of-the-year (YOY) and older fishes. Opaque bands form mainly in spring and summer, coincident with the reproductive season. Larger and older males reached 601 mm and eight years, while females reached 985 mm and 11 years. The assumed daily microincrements counts ranged from 127 to 196 for YOY of 135 to 184 mm TL. The common weight-length equation for grouped sexes was TW♀♂=0.000015TL2.93 (mm, g). The von Bertalanffy growth equations were: TL♀=1076(1–e–0.15 (t+0.78)); TL♂=652(1–e–0.28 (t+0.48)); and TL♀♂=839(1–e–0.20 (t+0.67)). Therefore, P. orbignyanus is a fast-growing and relatively short-living species for which females attain larger length and older ages than males, characteristics that have to be taken into account for its stock assessment and management.

Age, growth, and mortality of littlehead porgy, Calamus proridens, from southeast Florida coastal waters

Sectioned otoliths were used to age littlehead porgy Calamus proridens ( n = 737) from southeastern Florida recreational fisheries. Otolith sections contained easily identifiable annuli and were reliable structures for aging littlehead porgy up to 11 yrs. Opaque zones were deposited from March to June (peaking in April). Littlehead porgy ranged from 1 to 11 yrs and 220 to 385 mm total length (TL). Body size relationships were TL = 1.09 FL + 16.06 ( n = 3474, r2 = 0.95), FL = 0.87 TL – 1.15 ( n = 3474, r2 = 0.95), W = 4.76 × 10 –5 TL 2.80 ( n = 6722, r2 = 0.86), and W = 1.2 × 10 –4 FL 2.71 ( n = 3474, r2 = 0.90), where W is total weight (g) and FL is fork length (mm). Growth was not significantly different between two discrete geographic regions of Florida, and the von Bertalanffy growth equation was Lt = 335 (1 – e –0.41 ( t + 2.13) ) for all areas combined. The point estimate of natural mortality was M = 0.38, while age-specific estimates of M ranged from 0.60 to 0.41 yrs–1 for ages 1–11. Littlehead porgy were fully recruited to the headboat fishery by age- 3 and catch curve analysis resulted in an estimate of total mortality Z = 1.08 for ages 3–7+. This study reports first estimates of life history parameters for littlehead porgy from Atlantic waters of the southeastern United States.

Evaluation of cooking effects on otolith stable carbon and oxygen isotope values of teleostean fish Pomadasys kaakan (Cuvier, 1830).

For years, archaeologists, climatologists, and ecologists have used stable oxygen isotope values (δ13 C, δ18 O) in fish otoliths from archaeological sites to reconstruct the habitats, paleo-temperature, and seasonality of the fish captures. Otoliths from archaeological sites might have been heated when ancient people cooked the fish for food. Therefore, there are debates as to whether the cooking behaviors would cause further isotopic fractionations of the carbonate in the otoliths. In this study, we have evaluated the effects of the cooking methods on the otolith δ13 C and δ18 O values by comparing the otoliths of the javelin grunter (Pomadasys kaakan) from the same individuals, with the left otoliths taken out before the different cooking processes. Otolith sections of the fish were then made and several subsamples were milled along the microstructures visible in the otolith pairs, mostly annual check rings, followed by the stable isotope analyses. There were no morphological changes between the cooked and uncooked otoliths. The δ13 C and δ18 O values were highly consistent for the otolith subsamples between the cooked and uncooked pairs, suggesting none or trivial effects of the cooking processes on the isotopic values of the otoliths. In addition, some javelin grunters showed lower δ13 C (-5‰ to -6‰) and δ18 O (-4‰ to -5‰) values deposited in the wide translucent zone of the otoliths, suggesting seasonal migration of the fish to estuaries during the summer. This study suggests that cooking processes do not change otolith stable isotopic compositions and will therefore allow for future research to use the otolith δ13 C and δ18 O values to better understand the life history and used habitats of the preserved fish remains in the middens.

Exceptional longevity in a lightly exploited, semi-anadromous clupeid (Perth herring Nematalosa vlaminghi) within a degraded estuarine environment.

Many anadromous (and semi-anadromous) fish species, which migrate from marine to freshwater ecosystems to spawn and to complete their life cycle, are currently threatened by habitat degradation in the upper parts of estuaries and rivers, where spawning and juvenile nursery areas occur. This situation pertains to Nematalosa vlaminghi, a semi-anadromous gizzard shad (Clupeidae: Dorosomatinae) endemic to south-western Australia. More information on the biology of N. vlaminghi is required for its effective management and conservation. This study estimated growth, longevity and natural mortality of N. vlaminghi. Ages were determined by counting validated annual growth increments in thin sections of sagittal otoliths. Fish were sampled in the Swan-Canning Estuary, which historically hosted the main commercial fishery for N. vlaminghi. Since the late 1990s, however, only very minor catches of this species have been taken from this estuary and none since 2007. Given the essentially unexploited state of the current population, the estimate of total mortality (Z, y-1 ) from the catch curve analysis in this study provides a direct estimate of natural mortality (M, y-1 ) for N. vlaminghi. Somatic growth during this study was substantially slower than that historically reported for N. vlaminghi. Various processes operating in this estuary since the 1970s may have contributed to slower growth, including increased hypoxia, higher primary productivity due to eutrophication and cessation of fishing for N. vlaminghi. The maximum observed age of 19.8 years for N. vlaminghi is the highest reported for any gizzard shad globally and one of the highest reported for any clupeid species. This exceptional longevity is likely part of a life-history strategy that allows N. vlaminghi, which exhibits substantial variation in annual recruitment success, to persist in the intermittently closed estuaries of south-western Australia where environmental factors, including low flow and hypoxia, can create unfavourable conditions for reproduction for extended periods.

Demographics of Scomberomorus commerson in the Central Taiwan Strait

The narrow-barred Spanish mackerel Scomberomorus commerson is an economically essential species; however, few studies have investigated its demographic structure in the northwestern Pacific, which includes Taiwan’s waters. This study examined the growth parameters, age composition, mortality, and sex ratio of S. commerson catches by examining sagittal otoliths and other biological data collected in a 3-year project from June 2018 to June 2021. The transverse sections of sagittal otoliths exhibited alternating translucent and opaque zones, in annual cycles, and this observation was validated by otolith edge analysis. Opaque zones began to form in October; the growth peaked in December and lasted until March. Growth parameters were estimated for female (L∞ = 144.1 cm fork length [FL], k = 0.39 y−1, to = −0.85 y) and male (L∞ = 136.0 cm FL, k = 0.32 y−1, to = −1.49 y) specimens. The maximum recorded FL, body weight, and age were 159.0 cm, 27 kg, and 9.2 y for female and 135.0 cm, 17.8 kg, and 7.2 y for male specimens. Rapid growth was observed for both sexes, with FL reaching 66.8 ± 14.2 cm in female specimens and 70.1 ± 11.0 cm in male specimens during the first year of life. An age–length key based on the direct otolith aging and FL dataset (N = 646) was used to estimate the age composition of 3-year catches measured at landing (N = 16,133). The results verified that the S. commerson currently caught in the central Taiwan Strait are mainly young fish aged 1+ to 2+ y. The estimated fishing mortality (0.27 y−1) and exploitation rate (0.30) suggested that overfishing was not occurring in this stock. The findings of this study have helped clarify the population dynamics of the S. commerson in the Taiwan Strait, and the biological parameters reported herein can aid the management and conservation to ensure the sustainability of this species in this region.

Age and growth of Ceratoscopelus warmingii (Myctophidae) in the South China Sea based on sagittal otolith microstructure

ABSTRACT Age and growth of a dominant lanternfish Ceratoscopelus warmingii in the South China Sea were investigated based on sagittal otolith microstructure of juvenile and adult specimens collected in June 2015. The length–weight (L-W) relationship for C. warmingii was Wf = 0.00000814 L 3.1170 (females) and Wm = 0.00001071 L 3.3043 (males), revealing both positive allometric growth and non-significant difference between the sexes. Three distinct zones of the otolith microstructure were depicted, a central zone (CZ), middle zone (MZ) and external zone (EZ). Age was estimated by summing the daily growth increments in otolith sections on the assumption of daily deposition. The von Bertalanffy models of females and males were fitted as Lf = 75.9 [1−exp{−0.0074 (t−14.1)}] and Lm = 65.0[1−exp{−0.0097 (t−7.6)}], respectively. The maximum growth rates estimated were 0.319 mm day−1 for females and 0.345 mm day−1 for males, and thereafter the growth rate decreased with age. The back-calculated hatching date of specimens collected was determined as from August of last year to March of next year with a peak in winter. Theoretical maximum growth of C. warmingii appeared to occur near the metamorphic period.

Age estimation comparison between whole and thin-sectioned otoliths and pelvic fin-ray sections of long-lived lake trout, Salvelinus namaycush, from Great Bear Lake, Northwest Territories, Canada

Studies to determine precision and bias of both methods and age-readers are important to evaluate reliability of age data used for developing fisheries management objectives. We assessed within-reader, between-reader, and between-method precision (coefficient of variation, CV%) and bias of age estimations for long-lived lake trout, Salvelinus namaycush, from Great Bear Lake using three readers with different levels of experience. The assessment used independent age estimates (n = 3 per reader) from whole and transverse-sectioned otoliths (range = 1–67 years), and pelvic fin-ray sections (range = 3–26 years). We also examined between-method differences in assigned confidence scores. Within readers, age estimates from sectioned otoliths were more precise (2.6–3.0%) than whole (3.6–4.5%) otoliths. Between whole and sectioned otoliths, precision of age estimates was 5.4% and bias was low up to age 20. Age was typically under-estimated from whole otoliths compared to sections for fish ≥ 34 years. Increased reader confidence was correlated with greater precision and younger age estimates, particularly for whole otoliths, but less so for fin rays. Age was estimated with higher confidence from otolith sections than other methods. The least experienced reader estimated age with the lowest precision, and between-reader bias was evident among older ages. Age was consistently under-estimated and less precise from pelvic fins compared to sectioned otoliths, and are therefore an unsuitable non-lethal alternative. Sectioned otoliths revealed longevity was greater (67 years) than historically documented using whole otoliths (53 years) for these fish. Our findings contribute to those relying on otoliths or pelvic fin rays to estimate ages of long-lived lake trout populations, which are a key component of freshwater fauna in polar North America.

Age, growth, and reproductive parameters of four species of sea catfish (Siluriformes: Ariidae) from Kuwaiti waters

Age, growth, spawning season, and fecundity of four species of sea catfish inhabiting the northern Arabian (Persian) Gulf were investigated. These species constitute major bycatches of shrimp trawling and with lesser percentages in other fishing gears such as gill nets, gargoor traps, and hook and line setups, and most of these bycatches are eventually discarded. The most abundant catfish species found are Plicofollis tenuispinis and Netuma bilineata, while two other species, Netuma thalassina and Plicofollis dussumieri, are found in lower abundance. Length–otolith weight distribution showed a truncation in N. bilineata, which might indicate the presence of two sub-populations within Kuwait waters. Transverse sections of lapilli otoliths showed that annuli deposition occurs during the months of April and May. The von Bertalanffy parameters estimated for the four species showed that females of P. tenuispinis grow faster than males. Two presumptive sub-populations of N. bilineata inhabiting Kuwait waters showed a low growth rate population (K=0.27 y−1) and a higher growth rate population (K=0.35 y−1). The growth rate of N. thalassina was moderate (K=0.30 y−1), while the growth rate of P. dussumieri was relatively higher (K=0.34 y−1). The peak spawning season of the three major catfish species was from March to May, and data on fecundity and its relationship with body weight is presented. The fecundity of catfish species is low as is their market demand. However, the impact of shrimp trawling on the catfish population, as discarded bycatch, can have increasingly detrimental effects that on the overall population size and diversity of this population.

Age and growth of red-spotted grouper Epinephelus akaara collected from the coastal waters of Toyama Prefecture, Japan, determined by transverse otolith sections

Age and growth of red-spotted grouper <I>Epinephelus akaara</I> collected from the coastal waters of Toyama Prefecture, Japan, determined by transverse otolith sections