Search Results (41)

The Min pig, a Chinese indigenous breed, is valued for its excellent meat quality and stress tolerance. Nevertheless, its growth rate falls considerably short of commercial pig breeds, a pattern typical of most unselected indigenous populations, and marked individual variation further undermines its economic viability. To explore the genetic basis of this variation, we evaluated a series of nonlinear fixed-effects and mixed-effects models based on the Gompertz, Logistic, and von Bertalanffy functions using body weight records from 92 Min pigs. Model selection was based on AIC, BIC, and leave-one-out cross-validation. The best-fitting model was a Logistic nonlinear mixed-effects model with individual-level random effects on all three growth parameters (Asymptotic weight, timing parameter, and be parameter), which clearly outperformed models with simpler random-effect structures and fixed-effects models. From this model, we identified three characteristic growth transition points: the early transition point (Growth Rate Index, GRI) at 94.83 days (22.32 kg), the single inflection point (Maximum Growth Rate, MGR) at 166.06 days (52.80 kg), and the late transition point (Late Growth Rate Index, LGRI) at 237.29 days (83.29 kg), with a maximum absolute growth rate of 488.2 g/day. These points partitioned growth into initial acceleration, rapid growth, deceleration, and Asymptotic growth phases. Using individual fitted growth curves, we selected five fast-growing and five slow-growing pigs that reached approximately 90 kg during the plateau phase, defined as a predicted body weight of at least 95% of the individual Asymptotic weight. The fast-growing group reached 90 kg at 240.5 ± 20.42 days, whereas the slow-growing group reached the same weight at 286.67 ± 19.20 days. At the 90 kg slaughter weight, we collected longissimus dorsi muscle samples from these pigs during the plateau phase and performed RNA-seq. Transcriptome analysis revealed 864 differentially expressed genes between the two groups, with 540 upregulated and 324 downregulated in the fast-growing group. Pathway enrichment implicated the PI3K-Akt and TGF-β signaling pathways in muscle development, and differential expression of IGFN1, DCN, COL3A1, MYOC, COL1A2, COL1A1, and IGF2 may explain the growth variation between the groups. In summary, the Logistic mixed-effects model with individual-level random effects on all growth parameters effectively captures the growth pattern of Min pigs, and the PI3K-Akt and TGF-β pathways likely mediate growth differences in this breed. Full article

Body measurements provide a non-invasive basis for estimating live weight, yet their predictive value and age-related variation remain poorly characterized in female Jiangyue donkeys. Body weight (BW) and 11 morphometric traits were recorded in 484 females: withers height (WH), body length (BL), chest circumference (CC), cannon circumference (CAC), head length (HL), neck length (NL), chest width (CW), chest depth (CD), rump height (RH), rump length (RL), and rump width (RW). Descriptive statistics, correlation analyses, and regression analyses were performed using SPSS 27.0; stepwise regression was then applied to derive and validate BW prediction equations. Additionally, four nonlinear functions—Logistic, Gompertz, Brody, and von Bertalanffy—were fitted to cross-sectional BW data from 241 females sampled at different ages to characterize the population-level relationship between age and weight. BW was positively correlated with all morphometric traits (p < 0.01), with CC showing the strongest association. The optimal equations explained 91.8% and 84.4% of the variation in BW among growing and adult donkeys, respectively (both p < 0.01). Of the four nonlinear functions evaluated, the Brody model provided the closest fit (R² = 0.99960) and yielded an estimated asymptotic mature weight of 191.049 kg. Because the age–weight analysis was based on cross-sectional observations, the resulting curve represents population-level variation rather than within-animal growth trajectories. Collectively, these models offer quantitative tools for live-weight estimation, growth assessment, and herd management in female Jiangyue donkeys. Full article

In this study, we estimated the age and growth of S. niphonius using otolith-based age determination. Five hundred and thirty individuals were sampled from commercial fisheries and the National Institute of Fisheries Science research vessels in Korean waters between January and December 2024 and from June to September 2025. Fork length ranged from 30.4 to 112.1 cm and body weight ranged from 218.2 to 9360 g. Sagittal otoliths were transversely sectioned and examined under a microscope. The age-reading precision between the two independent readers exhibited a high agreement (percentage agreement = 96.0%, average percentage error = 5.49%, coefficient of variation = 7.76%). The observed age ranges were 0–10.1 years for females and 0–8.1 years for males. Estimated parameters of the von Bertalanffy growth function were $L_{\infty }=119.77$ cm, $K=0.41$ year⁻¹, and $t_0=-0.83$ for females, and $L_{\infty }=97.00$ cm, $K=0.59$ year⁻¹, and $t_0=-0.64$ for males. Females exhibited larger asymptotic lengths but lower growth coefficients than those of males, and growth differed significantly between sexes. These results constitute the first study of age and growth based on otoliths in Korean waters and contribute to improving the biological understanding and management of this species. Full article

Binary logistic regression relies on the symmetric logit link, whose fixed inflection point cannot adapt to asymmetric response mechanisms and so may yield miscalibrated probabilities when the true response curve is asymmetric—a problem that can be particularly consequential in rare event or imbalanced applications. This study proposes a flexible, asymmetric link derived from the von Bertalanffy growth equation and tests a single, calibration-oriented hypothesis: estimating an asymmetric link improves the calibration of the predicted probabilities under asymmetric response mechanisms while leaving discrimination unchanged. The single shape parameter ν (the reparameterized von Bertalanffy shape, ν = m − 1; the growth curve baseline parameter is absorbed into the intercept and is not separately identifiable) is estimated jointly with the regression coefficients by L2-penalized maximum likelihood, giving a coherent generalized linear model rather than a post hoc re-thresholding of logistic scores; the logistic link is nested exactly at ν = 1 (m = 2), so the model reduces to ordinary logistic regression whenever the logit is adequate. The link was benchmarked on identical out-of-sample partitions against four competitors—logistic regression at the 0.5 cut-off, threshold-optimized logistic regression, ridge-penalized logistic regression at the same penalty (which separates the link from the regularization it requires), and Stukel’s generalized logistic model—across a correctly specified logistic mechanism and two asymmetric mechanisms (a complementary log–log mechanism and a von Bertalanffy-type best-case reference), three class imbalance ratios (0.10, 0.25, and 0.50) and five sample sizes (100–10,000), for 45,000 iterations in total. Paired differences were summarized by the Hodges–Lehmann median difference, its 95% confidence interval, and the rank-biserial correlation, with Benjamini–Hochberg control of multiplicity. The results supported the hypothesis. At moderate-to-large sample sizes, and increasingly as prevalence approached 0.50, the proposed link achieved lower Brier score and Log–Loss values than the three logistic competitors under both asymmetric mechanisms—for example, a median Log–Loss reduction against the matched-penalty ridge model of about 0.004 at balanced prevalence and the largest sample (95% confidence interval excluding zero; rank-biserial ≈ −1)—an advantage small in absolute size but, at the larger sample sizes, consistent across essentially every replication, and increasing with sample size and prevalence. Discrimination showed no practically important differences at moderate-to-large sample sizes: the area under the ROC curve and overall accuracy were essentially the same across the five methods, so the flexible link improves the quality of the probabilities without degrading class separation. Under the correctly specified logistic mechanism, the method showed no material deterioration, which is consistent with its exact nesting of the logistic model. The contribution is a growth curve-motivated asymmetric link that improves probability calibration under response asymmetry while preserving discrimination and recovering the logistic model when it is adequate. Full article

Human-mediated species translocations are increasingly interacting with global climate change, yet empirical insights into how introduced populations achieve long-term demographic stability in new frontiers remain limited. This study systematically investigates the post-translocation establishment and multi-generational persistence of the endemic cyprinid Squalidus multimaculatus at its newly identified northern distribution limit in Goseong, Republic of Korea, following historical human-mediated introduction. Utilizing nationwide multi-decadal occurrence records, we mapped the species’ spatio-temporal dynamics across three temporal phases (T₀, T₁, and T₂). Long-term biogeochemical water quality indices and thermal regimes were compared between the native baseline (Yeongdeok) and Goseong. Furthermore, demographic shifts and growth trajectories were evaluated using 676 field-sampled specimens through length–weight relationships, condition factor (K_F) analysis, age structure mixture modeling, and the von Bertalanffy growth function (VBGF). Our results indicate that the Goseong habitat provides generally favorable biogeochemical conditions characterized by low nutrient loading and high dissolved oxygen stability. Crucial to this transition, a distinct winter warming shift expanded the available thermal window, reducing the frequency of extreme winter cold-stress events (≤2.0 °C) from 40.0% to 6.9%. Concurrently, the post-translocation population exhibited successful demographic stability, characterized by a self-sustaining age structure (ages 0+ to 4+), an inferred spawning window during June–July, and a growth trajectory (L_∞ = 95.69 mm) broadly comparable to native benchmarks. These findings establish a reliable empirical baseline framework linking human-mediated introductions with long-term environmental transitions. Globally, this case study suggests that post-translocation success depends on the interplay between introduction pathways and climate suitability, offering key insights into population survival and ecosystem evolution under global change. Full article

Understanding individual growth is essential for assessing exploitation status and supporting sustainable fishery management. For the southern Brazilian stock of the mullet Mugil liza, previous growth estimates were based on whole otolith readings and included few young individuals, potentially influencing growth parameter estimation and stock assessment outputs. In this study, daily otolith microincrements of juveniles were validated using oxytetracycline (OTC) marking and combined with age–length data from a previous study to evaluate the effect of incorporating validated juvenile ages into von Bertalanffy growth function estimates. The updated model yielded a 15% smaller asymptotic length (564 mm), a 47% higher growth coefficient (0.28 yr⁻¹), and a theoretical age at zero length closer to biologically plausible values (t0 = −0.11). Revised growth parameters were incorporated into an age-structured production model (ASPM). Although temporal trends in spawning biomass and fishing mortality remained similar, substantial differences were observed in biomass scale and biological reference points. These findings highlight the sensitivity of stock assessment outputs to growth parameterization and the importance of adequately representing early life stages in growth models. Full article

To investigate the age and growth characteristics of the pointhead flounder (Cleisthenes pinetorum) in the West Sea (Yellow Sea) of Korea, samples were collected from bottom trawl vessels throughout 2019. A total of 1116 individuals (1015 females and 101 males) were analyzed. Because specimens were obtained from commercial landings, only fish of approximately 20 cm or larger were available due to marketability constraints. The body weight (BW) − total length (TL) relationships were BW = 0.00001TL^3.3443 (R² = 0.9279) for females and BW = 0.000002TL^3.2659 (R² = 0.9347) for males. The observed sex ratio (male:female = 1:10) was strongly female-biased; however, this likely reflected the underrepresentation of smaller males in commercial catches rather than the natural population structure. Females also exhibited larger body lengths than males. Otoliths were generally round, with a slightly elongated anterior region, and measurements were taken along the longest axis from the core to the margin. The relationship between TL and otolith radius (R) was expressed as TL = 8.0342R + 5.6218 (R² = 0.8408). Growth equations were estimated for both sexes; however, because older males were poorly represented, the male von Bertalanffy growth function was fitted with the asymptotic length fixed to 43.3 cm (110% of the observed maximum male TL). Annuli were formed annually in November, and the spawning season was identified as September–November, suggesting a close association between annulus formation and the spawning period. The von Bertalanffy growth equations were Lt = 57.66(1 − exp[−0.1865(t + 0.46)]) for females and Lt = 43.3(1 − exp[−0.2679(t + 0.5490)]) for males. Full article

Small pelagic fishes are essential for artisanal fisheries and food security in São Tomé and Príncipe, yet biological information required for stock assessment remains scarce. This study examined the population dynamics and life-history traits of Caranx crysos, Euthynnus alletteratus, Hemiramphus balao, and Cheilopogon melanurus using 9052 specimens collected from artisanal landings between 2023 and 2025. C. melanurus (35.2%) and H. balao (34.0%) dominated the sampled catches, followed by C. crysos (18.1%) and E. alletteratus (12.7%). Standardized CPUE series modelled using GAMs revealed significant temporal and seasonal variation in relative abundance, with contrasting species-specific trends. Length–weight relationships revealed negative allometric growth in three of the four species examined (75%), with b values ranging from 2.50 to 3.19, while Fulton’s condition factor differed significantly among species (Kruskal–Wallis χ² = 6702.7, p < 0.001). Sex-ratio analyses showed significant deviations from parity in C. crysos and C. melanurus, whereas E. alletteratus and H. balao remained balanced. Gonadosomatic index and maturity-stage distributions indicated year-round reproductive activity with distinct spawning peaks. Length at first maturity (L50) ranged from 30.2 cm to 38.8 cm among species. Growth parameters estimated from length-frequency data using the von Bertalanffy Growth Function fitted through ELEFAN_GA in TropFishR yielded L∞ values of 43.9–68.4 cm and K values of 0.065–0.336 yr⁻¹. Growth performance index (φ′) ranged from 2.48 to 2.99, corresponding to theoretical longevities of 8.9–46.3 years. Length-based cohort analysis indicated biomass concentration in intermediate size classes and increasing fishing mortality towards larger individuals. Exploitation rates revealed contrasting fishing pressures among species, while sensitivity analyses identified growth and mortality parameters as the main sources of uncertainty. These findings provide the first integrated biological baseline for the assessment and management of small pelagic resources in São Tomé and Príncipe. Full article

Freshwater ecosystems in southern Europe are increasingly impacted by fish invasions from central and northern regions, often facilitated by warmer climates and reduced natural-enemy pressure. The European catfish (Silurus glanis), the largest freshwater fish in Europe, is now widely established across various southern European basins, where its high fecundity, ecological plasticity, and predatory behaviour pose significant risks to native communities. Despite its rapid spread, growth dynamics across native and non-native populations remains scatteredly described in studies with different approaches. Objective: This study compares growth rates between native populations in the Czech Republic and non-native populations in Portugal, Spain, and Italy, and assesses whether growth rates are influenced by introduction timelines, reflecting differences in population age and invasion stage. Methodology: Nine populations spanning the native range (central Europe) and non-native range (southern Europe) were analysed. A total of 427 different vertebrae were used to age the fish and growth was modelled using the von Bertalanffy growth function. Generalised linear models were used to identify environmental and demographic predictors of variation in the growth coefficient (K). Moreover, mark-recapture data from the native populatations was also analysed. Results: Preliminary results indicate substantial variation in growth among populations, with higher growth rates exhibited in non-native populations (Iberian), while native populations showed consistently lower growth rates. Growth was primarily associated with population age and minimum temperature, decreasing with increasing population age and increasing under warmer thermal conditions. These patterns suggest faster growth in recently established and warmer populations. Conclusions: Growth dynamics of European catfish vary markedly across native and non-native ranges, driven mainly by thermal conditions and invasion history. Faster growth in warmer and recently established populations may enhance invasion success by accelerating size-at-age and reproductive potential. This study highlights the importance of integrating environmental and demographic factors to improve predictions of invasion dynamics and ecological impacts in freshwater ecosystems. Full article

This paper investigates the optimal harvesting of a nonlinear, size-structured population governed by a first-order transport equation with nonlocal environmental crowding feedback and exogenous inflow. First, we establish finite-horizon well-posedness for the controlled state system in an $L^1$ framework, proving the existence, uniqueness, positivity, and continuous dependence of weak solutions. Second, we show that the infinite-dimensional stationary problem reduces exactly to a scalar nonlinear closure equation, yielding existence and conditional uniqueness results for stationary states. Within this equilibrium framework, we distinguish the persistence of the forced system from intrinsic demographic self-replacement and introduce size-continuous per-recruit and spawning-potential diagnostics. Finally, we formulate a partial differential equation (PDE)-constrained optimal harvesting problem. Under a compactness assumption on the control-to-state map, we establish the existence of optimal controls. We then formally derive a Pontryagin-type first-order optimality system for the harvesting problem. The variation of the nonlocal environmental feedback produces a coupled integral source term in the adjoint equation. The associated pointwise maximization condition yields a bang–bang harvesting structure, while a monotone size-threshold policy is shown to require an additional single-crossing assumption on the switching function. These hypotheses are illustrated using a fisheries model with density-dependent von Bertalanffy growth. Full article

The sandfish (Arctoscopus japonicus) is an important fishery resource in the East/Japan Sea; however, its stock has recently declined sharply. Most ecological studies were conducted before the mid-2000s, limiting our understanding of recent ecological changes under rapidly changing environmental conditions. We aimed to analyze recent ecological characteristics of sandfish, including growth, maturation, and feeding ecology, in eastern Korean waters. Sandfish samples collected between 2021 and 2024 were analyzed. Age and growth were estimated using otolith-based analyses and the von Bertalanffy growth function. Maturation characteristics were evaluated using gonadosomatic index and maturity-stage analyses, and feeding ecology was assessed through stomach content analysis. Younger individuals (aged 1–2 years) exhibited larger body sizes than previously reported, whereas older individuals (3–5 years) exhibited relatively smaller body sizes. The peak spawning period occurred from December to January, indicating a delay in spawning compared with earlier studies. The length at 50% maturity was estimated at 16.3 cm, corresponding to 1.72 years. Euphausiacea and Amphipoda were the dominant prey items. These findings provide updated baseline information on recent ecological changes in sandfish populations and may support future stock assessment and fisheries management. Continued long-term monitoring is needed to better understand environmental influences on sandfish ecology. Full article

Lanternfishes (Myctophidae) dominate mesopelagic ecosystems and play a central role in pelagic food webs through their high biomass and diel vertical migration, yet detailed information on their age structure and growth dynamics remains limited in the Northwest Pacific Ocean. This study reconstructs age, growth patterns, and life-history strategies of D. gigas and D. perspicillatus using sagittal otolith microstructure analysis. Specimens were collected during oceanographic surveys conducted in 2023 and 2024, and individual ages were estimated by counting daily otolith growth increments. Somatic growth trajectories were evaluated using multiple nonlinear growth models, including the von Bertalanffy, Gompertz, and Logistic functions, and growth dynamics were further assessed through derivative-based growth speed analyses. The results reveal pronounced interspecific differences in growth strategy and longevity. D. perspicillatus exhibited rapid early somatic growth, a compressed age structure, and an early approach to asymptotic length, indicating a short-lived life-history strategy characterized by early growth deceleration and high population turnover. In contrast, D. gigas showed faster early growth, prolonged somatic development, greater inter-individual variability, and substantially larger maximum body size, reflecting delayed maturation and extended lifespan. Otolith microstructural zonation clearly corresponded to larval, juvenile, and adult growth phases in both species. The predominance of younger age classes in the catch and interannual differences in size structure were primarily attributed to ontogenetic habitat shifts, cohort composition, and sampling availability rather than intrinsic changes in growth dynamics. Full article

This study investigates the population dynamics of the freshwater bream (Abramis brama) in the Lower Danube River between 2021 and 2025, focusing on growth parameters, mortality rates, length-based recruitment estimates, and the influence of hydrological and water physico-chemical factors. A total of 685 individuals were collected, with an average total length of 31–32 cm and a balanced sex ratio. Growth parameters estimated using the von Bertalanffy Growth Function (VBGF) revealed an asymptotic length (L∞) ranging from 39.9 cm (2021) to 55.7 cm (2024) and growth coefficients (k) between 0.80 and 1.40 year⁻¹. The total mortality (Z) varied from 2.19 to 5.24 year⁻¹, while the exploitation rate (E) reached a maximum of 0.73 in 2025, indicating increased fishing pressure. Length-based recruitment analyses showed a unimodal seasonal pattern, with peak recruitment occurring between June and October and maximum monthly values recorded in September 2025 (29.89%). Pearson correlations indicated that recruitment was positively related to water temperature (r = 0.65) and negatively to average water level (r = –0.63). Recruitment estimates are derived from length-frequency back-calculation and reflect proxies of cohort entry into the exploited stock rather than direct juvenile abundance. These results indicate a consistent seasonal pattern of cohort entry within the exploited component of the population and highlight the role of temperature and river discharge in modulating length-based recruitment signals under variable hydrological conditions. Full article

Effective fisheries management relies on accurate stock assessments to ensure sustainable exploitation and long-term ecosystem stability. Fisheries from the Nile Delta lakes of Egypt—comprising Manzala, Burullus, Edku, and Mariout—are economically critical, collectively contributing about 40% of the nation’s total capture fisheries and are facing severe anthropogenic challenges. This study assessed the stock status of 10 key fish species and two crustacean species from these four Nile Delta lakes by determining their life history parameters and exploitation levels. The analysis included estimation of the Length–Weight Relationship (LWR), von Bertalanffy Growth Function (VBGF) parameters, instantaneous mortality coefficients (Z, M, F), and the exploitation ratio (E). Asymptotic total length (L∞) varied widely, ranging from 10.47 cm for Portunus pelagicus to 86.78 cm for Clarias gariepinus (in Lake Manzala). The growth coefficient (K) spanned from 0.31 yr⁻¹ (C. gariepinus) to 1.79 yr⁻¹ (Metapenaeus stebbingi), reflecting diverse life history strategies. The key finding, based on the Gulland criterion, is that all commercial stocks examined in the Nile Delta lakes are currently subjected to severe overexploitation, with the exploitation ratio (E) consistently exceeding the optimal threshold of 0.5. These results underscore the urgent need for adaptive management strategies, including stricter gear regulations and improved fisheries monitoring, to ensure the sustainability of these vital resources. Full article

The aim of this work is to model the growth of an economic system and, in particular, the evolution of capital accumulation over time, analysing the feasibility of a closed-form solution to the initial value problem that governs the capital-per-capita dynamics. The latter are related to the labour-force dynamics, which are assumed to follow a von Bertalanffy model, studied in the literature in its simplest form and for which the existence of an exact solution, in terms of hypergeometric functions, is known. Here, we consider an extended form of the von Bertalanffy equation, which we make dependent on two parameters, rather than the single-parameter model known in the literature, to better capture the features that a reliable economic growth model should possess. Furthermore, we allow one of the two parameters to vary over time, making it dependent on a periodic function to account for seasonality. We prove that the two-parameter model admits an exact solution, in terms of hypergeometric functions, when both parameters are constant. In the time-varying case, although it is not possible to obtain a closed-form solution, we are able to find two exact solutions that closely bound, from below and from above, the desired one, as well as its numerical approximation. The presented models are implemented in the Mathematica environment, where simulations, parameter sensitivity analyses and comparisons with the known single-parameter model are also performed, validating our findings. Full article