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The objective of the present study was to examine the length-weight relationships and condition factors of snapper Lutjanus russellii, ponyfish Aurigequula fasciata and white-spotted spinefoot Siganus canaliculatus harvested from Ulelhee Bay, Banda Aceh City, Indonesia. These species are the predominant fishes caught by traditional beach trawl in Ulelhee Bay, Banda Aceh City, Indonesia. The sampling was conducted for three months from April to June 2015 at one-week interval. A total of 900 fish samples (300 individuals for each species) were measured for the total length and body weight. The length-weight relationships were calculated using Linear Allometric Model (LAM), while the relative weights (Wr) and Fulton’s condition (K) factors were calculated to assess the condition of the fish samples. The results showed that the b value of 3.04 in snapper indicates isometric growth pattern, while ponyfish and white-spotted spinefoot fish had the b values of 1.41 and 1.75, respectively, and these species display an allometric growth pattern. The average Fulton’s condition factor (K) of snapper was 3.01 for male and 2.49 for female; female ponyfish has the K value of 2.92 and 2.92 for male. In addition, the average K value of whitespotted spinefoot was 2.61 and 2.59 for female and male, respectively. The relative weight condition factor ranges from 58.73 to 166.09 for snapper, from 70.55 to 129.65 for ponyfish, and from 71.63 to 133.53 for white-spotted spinefoot. In general, the relative weight condition factors tendedto be 100. It is concluded that snapper has isometric growth pattern, while ponyfish and white-spotted spinefoot display the negative allometric growth pattern. The condition factors are in excellent condition and indicate a balance of prey and predator.

This study investigates biometric relationships in Oreochromis niloticus (gray tilapia) reared in controlled pond environments at the Centro de Investigación Piscícola (CINPIS), Universidad Nacional Agraria La Molina (Perú), over a 3-year period (2021–2023). Focusing on total length ( L t ), standard length ( L s ), height ( H ), and width ( A ), we developed models to estimate weight ( W ) based on these parameters, achieving strong model performances with R 2 values between 0.899 and 0.994. The model using L t as a predictor of W proved most accurate with a mean relative error (MRE) of 11.2%, while models incorporating additional dimensions ( H and A ) did not enhance predictive accuracy. Comparative analyses show our model aligns with some studies on tilapia, though variations in L-W relationships due to environmental and breeding conditions are evident. Our results affirm the utility of L t in non-invasive biomass estimation for aquaculture, while highlighting the limitations of applying these models universally across different conditions and fish populations. Condition factor ( K ) and relative condition factor ( K r ) analyses further demonstrated stable and optimal growth conditions (mean K ≈ 1.76; K r ≈ 1.01) for tilapia under local culture practices. Accordingly, we propose the L-W relationship W = 0.0265 L 2.8469 for estimating the weight of gray tilapia grown in ponds with groundwater. This study provides a basis for the development of biomass estimation methods based on active acoustics or stereo video.

Slimy sculpin (Cottus cognatus) are increasingly being used as indicator species. This has primarily entailed measuring their condition, the assumption being that condition can be used as a surrogate for lipid content. While there is evidence to suggest this assumption is applicable to some fish, it has yet to be validated for C. cognatus. Further, there are several means by which one may calculate condition, the most commonly employed of which are indirect measurements of lipid content (namely, Fulton’s K, somatic K (Ks), and Le Cren’s relative condition factor (Kn)). We compared the ability of each of these morphometric indices to predict whole-body lipid content in C. cognatus. There was a moderate degree of evidence that Fulton’s K, Ks, and Kn are reliable predictors (Ks and Kn in particular). Of the latter we recommend Kn be used because, unlike Ks, it does not require that fish be killed. And while Fulton’s K did not perform quite as well, we consider it a sufficient substitute if the data necessary to calculate Kn are unavailable.

The main objectives of the present study were to determine the species composition of Caspian shad, genus Alosa and to estimate the LWR, CF, and Kn of A. braschnikowi and A. caspia during different months in the southeastern coast of the Caspian Sea. Two fishing methods, small mesh size beach seine and gillnet were used from December 2013 through July 2014. A. braschnikowi and A. caspia, were distinguished in the southeastern part of the Caspian Sea (Goharbaran), consisting of 57.1% and 42.9% of the Alosa catch, respectively. The slopes (b values) of the length-weight regression were 3.241 and 2.844 which were significantly different from 3 (P<0.05), indicating positive and negative allometric growth, respectively. The average CF of A. braschnikowi and A. caspia were calculated as 0.72 ± 0.12 and 0.83 ± 0.13, respectively. The average CF for both species were significantly different among months (P<0.001). There was a significantly negative correlation between size classes and CF of A. caspia. The Kn was greater than 1 for A. braschnikowi and lower than 1 for A. caspia indicating good well-being of A. braschnikowi as opposed to A. caspia in the southeastern Caspian Sea.

The stone moroko (Pseudorasbora parva) is an invasive species which spreads rapidly in European water bodies and occupies free ecological niches. In the years 2019-2020, monthly analyses of its population structure were carried out in the Wardynka River (western Poland), determining the age, size (TL and SL), body weight, growth, Fulton's condition factor, and the parameters of the length-weight relationship. In addition, quantitative descriptions of the parasite communities were made. End-point PCR was used to verify the presence of Sphaerothecum destruens in the fish. The age structure of the population was dominated by fish at the age of 1+ to 3+, and the maximum age was 5 + . The TL of the fish ranged from 2.50 to 10.60 cm (average 6.24 cm), SL from 2.10 to 9.50 cm (average 5.20 cm), and body weight from 0.15 to 11.43 g (average 2.74 g). The average body weight and length of males were higher than in females. The average Fulton's condition factor for the whole sample was 1.44 ± 0.24 and was similar for both sexes. The slope of the regression line (b > 3) indicates an allometric relationship between the length and weight of fish of both sexes. Back-calculated estimates of standard length fitted the von Bertalanffy growth function, although Taylor's criterion showed that the asymptotic length (Linf) was overestimated. Comparison of the von Bertalanffy growth function parameters revealed differences between sexes. The presence of parasites not previously recorded in stone moroko in Poland was confirmed: Dactylogyrus squameus, Phyllodistomum elongatum, P. folium, Posthodiplostomum cuticola (metacercaria), and Bivalvia gen. sp. (glochidia). Electrophoresis of the end-point PCR product did not reveal any signs of amplification for either of the primer sets used. S. destruens was not detected in any of the analysed samples of stone moroko.

Summary Background: The mullet fish Liza macrolepis and Moolgarda engeli are prominent in the waters of Lambada Lhok in Aceh province. At present, no scientific report on this species in Aceh waters is available. Therefore, the objective of the present study is to examine the growth pattern and condition factor of the species of mullets L. macrolepis and M. engeli harvested from the aforementioned coastal waters. Methods: Sampling occurred in three locations in the Lambada Lhok waters from July to November 2018. The fish were captured using gillnets from 6:00 AM to 3:00 PM four times a month for five months. A total of 242 L. macrolepis and 109 M. engeli were used for the analysis. The growth pattern was analyzed using a linear allometric model; then, two condition factors, Fulton's and relative weight, were calculated. Results: The study revealed a b value of 2.49 for males L. macrolepis and 1.81 for females. The b value was 3.22 for males M. engeli and 3.41 for females. The b value of the fish was higher during the dry season. The Fulton's condition factor of the male L. macrolepis was 1.19 and was 1.19 for the females. The relative condition factor of this species was 100.11 and 100.01 for males and females, respectively. The Fulton condition factor of M. engeli males was 1.05 and 1.06 for females. The relative weight condition factors were 101.08 and 100.61 for the males and females, respectively. Conclusions: The growth pattern of M. engeli tends to be isometric, whereas L. macrolepis has a negative allometric growth pattern. The condition factors indicate that the Lambada Lhok waters are still in good condition and support the growth of the mullets, but M. engeli is more adaptable than L. macrolepis.

Romania has a rich hydrographic network, which permitted the construction of over 80 large dams on its water courses, estimating a number between 545 and 674 hydropower plants that were either built or were in a different construction stage on the rivers of Romania in 2021. These hydropower plants were often built outside specific legislation regarding ecological impacts, especially before 1990. Longitudinal fragmentation of rivers causes severe ecological impacts on biodiversity, food chains, and nutrient cycles. Someșul Cald River is the main tributary of Someșul Mic River, the most important water source for the northwestern region of Transylvania. On its course, several dams and reservoirs were built from 1968 to 1980 for electricity production and population freshwater supply. The present study aimed to analyze the length–weight relationships (LWRs) and condition factors occurring in the longitudinally fragmented Someșul Cald River. The LWRs, relative condition factor Kn, and Fulton condition factor K were determined based on total length and wet body weight. Comparisons of LWRs, Kn, and K across river sections constrained by dams showed that some fish species exhibited similar growth patterns and physiological conditions, while others differed significantly. Freshwater fish physiology is altered by longitudinal fragmentation, both natural and artificial. Barriers such as dams influence the energy gradient, limiting feed availability and, consequently, the life history of fish species. Long-term management plans regarding conservation should take into consideration existing fish species population dynamics, along with their physiological and somatic status.

European hake (Merluccius merluccius) is a commercially important resource in Iberian Atlantic waters. Despite the recovery plan implemented in 2006 and the multiannual management plan for western waters, fishing mortality is still higher than that corresponding to the maximum sustainable yield for the southern European hake stock. The biological processes underlying the dynamics of this stock and its life history traits are essential for assessing population productivity and resilience, making them basic information for management. We analysed the temporal variability of size at maturity (L50) of this species and the main factors influencing it in Atlantic Iberian waters from 1982 to 2019. The annual variability of L50 for each sex was modelled with generalized additive models, considering explanatory environmental variables (Atlantic Multidecadal Oscillation, North Atlantic Oscillation and sea surface temperature) and biological variables (biomass, spawning biomass at length and relative condition factor). The results showed that the L50 of males decreased by a total of 12.9 cm and L50 of females decreased by a total of 10.9 cm from 1982 to 2019. For females the significant explanatory variables were year, spawning biomass at length, biomass and the North Atlantic Oscillation, while for males only year was an explanatory variable. These results are important for understanding the status of the European hake population, signalling that L50 is a good indicator for predicting future population dynamics.

For aquaculture assessments, the length-weight relationship and condition factor are considered as standard methods for determining fish growth, its health and the potential yield. A year-long study was conducted to calculate length-weight relationships (LWRs) and condition factor (K) for seven fish species, Schizothorax niger (Alghad or snowtrout), S. curvifrons (Sattar snowtrout), Cyprinus carpio (Common carp), Carassius carassius (Crucian carp), Pethia conchonius (Rosy barb), Crossocheilus diplochilus (Kashmir latia) and Gambusia holbrooki (Mosquito fish) in Manasbal Lake. The results revealed that four captured fish species (S. niger, S. curvifrons, C. diplochilus and G. holbrooki) exhibited negative allometric growth, while other fish species (C. carpio, C. carassius, P. conchonius) exhibited positive allometric growth. LWR was significant at P < 0.01 in all seven fish species, with a coefficient of determination (R2) ranging between 0.73 to 0.96. The K was higher in C. carpio than C. carassius, P. conchonius, G. holbrooki, C. diplochilus, S. niger and S. curvifrons. The current study providing the LWRs and condition factor of seven fish species from Manasbal Lake, Kashmir will be helpful for the management of fish species as well as for assessing the ecological condition of the Lake.

In this paper, the quantitative Geological Strength Index (GSI) for Singapore’s sedimentary rock mass is determined by applying four different approaches proposed by Hoek et al. (Quantification of the geological strength index chart, 2013 ), Cai et al. (Int J Rock Mech Min Sci 41(1):3–49, 2004 ), Sonmez and Ulusay (Int J Rock Mech Min Sci 36:743–760, 1999 ) and Russo (Improving the reliability of GSI estimation: the integrated GSI-RMi system, 2009 ) respectively. The relevant rock mass properties, including blockiness and discontinuities surface conditions, of 420 excavated rock faces in a Singapore’s underground excavation project are assessed for such determination. The results obtained by these different approaches are observed falling approximately in the same range between 45 and 55. Moreover, those quantitative GSI results are in good correlation with qualitative GSI which were assessed on excavated rock faces using Hoek et al. (Support of underground excavations in hard rock, Balkema, Rotterdam, 1995 ) approach. This study demonstrates that the four different approaches perform well by giving similar range of results, although different input parameters are applied in the calculation. A new GSI relationship between joint condition factor Bieniawski (Engineering rock mass classification, Wiley, New York, 1989 ) and RQD (rock quality designation) is also proposed to better match the qualitative GSI values.