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Total length‐weight relationships among Thai freshwater fishes and the influence of capture location and preservation
Journal of Applied Ichthyology
Abstract
Total length-weight regressions on logarithmic transformed data are provided for 33 species, with 26 apparently being first estimates. All regressions are highly significant with slope values between 2.5720 and 3.4436. Slopes and intercepts of length-weight regressions did not differ significantly with location for each of three species. Preservation in 10% formalin for 10 days followed by 30 days in 70% ethanol did not significantly influence regression slopes for the three species, length ranges and/or locations examined (ancova). Significance among regression intercepts was equivocal with ancova analyses mostly suggestive of differences and overlap of 95% confidence limits mostly suggestive of similarities.
... Similarly, length can increase [5,9] or decrease [4,8,11]. Still other studies did not fnd a signifcant difference in either length or weight after preservation [12,13]. ...
... However, LWR studies give little or no attention to the percentage of bias (from both under-and overestimation) that could infuence analyses [7]. Beamish [13] reported no signifcant diferences when comparing the slopes and intercepts from length-weight regressions of fresh and preserved fsh of the Tailand freshwater catfsh Glyptothorax major. However, the study found signifcant diferences in the slopes but not the intercepts for Cypriniformes Homalopteroides smithi and Schistura kohchangensis; all were fxed in 10% HCOH followed by preservation in 70% EtOH. ...
Length-weight relationship (LWR) studies are important for fish taxonomical analysis, ecological assessments, management, and conservation practices. Although LWR studies can use measurements of either fresh or preserved specimens, few studies have directly compared these methods. This study analyzed the effect of preservation on LWR of ten small-sized freshwater fish species from the Curaray River basin (Napo Basin), eastern Ecuador. 255 wild specimens were measured, weighed, fixed in formalin, and finally preserved in 70% ethanol. 287 specimens from the same species batch were measured again after preservation. We estimated LWR curves with linear regressions and compared slopes and intercepts between fresh and preserved specimens. The preservation process altered weight significantly for all ten species and altered both weight and length for two species. The magnitude of change varied according to the morphology and maximum size of each species. Smaller individuals exhibited greater proportional weight losses. LWR estimates for eight of the species are new to science. These results present new evidence of the preservation effects in LWR studies as well as a compilation of the varying results reported in the literature. We conclude that measurements on fresh specimens should be encouraged for LWR studies. However, recognizing that this is not always feasible, studies using preserved specimens should consider the effects of preservation on body length and weight.
... Similarly, length can increase [5,9] or decrease [4,8,11]. Still other studies did not fnd a signifcant difference in either length or weight after preservation [12,13]. ...
... However, LWR studies give little or no attention to the percentage of bias (from both under-and overestimation) that could infuence analyses [7]. Beamish [13] reported no signifcant diferences when comparing the slopes and intercepts from length-weight regressions of fresh and preserved fsh of the Tailand freshwater catfsh Glyptothorax major. However, the study found signifcant diferences in the slopes but not the intercepts for Cypriniformes Homalopteroides smithi and Schistura kohchangensis; all were fxed in 10% HCOH followed by preservation in 70% EtOH. ...
... Selangor shows similar pattern of indistinctly higher micro minerals content compared to samples from both Perak and Terengganu. Results indicated that different location does not have a big impact on the mineral compositions and this observation is similar to another observation on Thailand freshwater fish species that were collected from different locations [35]. Magnesium and calcium content in Monopterus albus sampled from Selangor were significantly higher (p<0.05) ...
Rice field eel (Monopterus albus) is an air breather freshwater fish that can be found extensively in paddy field area in Malaysia. It has high economic value all over Asia and used as folk remedies for various diseases. Mineral compositions play a vital role in various metabolisms though it's required in a minute amount in the human body. Proximate compositions and selected minerals compositions were determined in Monopterus albus. The study found that Monopterus albus was high in protein content (50.07%-74.31%) and low in lipid (2.26%-2.66%), which suggests this fish species suitable to be consumed by various human conditions. The amplest macroelement was Calcium with a concentration of 29127.00 mg/Kg - 50468.50 mg/Kg, followed by Phosphorus and Magnesium, 21290.00 mg/Kg - 32975.50 mg/Kg and 1264.50 mg/Kg - 1638.50 mg/Kg respectively. Zinc was the dominant microelement found in Monopterus albus with a concentration of 44.17±1.20 mg/Kg followed by Iron, Manganese, Copper, and Chromium with concentration range of 32.60 mg/Kg - 38.6 mg/Kg, 3.40 mg/Kg – 22.65 mg/Kg, 0.97 mg/Kg - 1.07 mg/Kg and 0.59 mg/Kg - 0.78 mg/Kg respectively. The results of this study will be further used to promote fish-based medication and remedies benefit to human. Â
... Morphological variations associated with preservation of juvenile or adult fishes have rarely been reported. Changes have mainly been based on length or proportion measurements (Leslie and Moore 1986, Sagnes 1997, Smith and Walker 2003, Paradis et al. 2007, Florin and Lingman 2008, Wessels et al. 2010, Lee et al. 2012), or length–weight relations (Al-Hassan et al. 2000, Ogle 2009, Beamish et al. 2011). To our knowledge, few studies explore the effect of preservation by taking advantage of the benefits of geometric morphometrics (BerbelFilho et al. 2013, Gaston et al. 2013). ...
Background. In taxonomic studies of fish, the use of preserved samples has been a common practice. Under the framework of morphometrics, the effect of the preservation techniques on body shape is rarely taken into account. Changes during preservation can cause errors in the results, which may eventually lead to wrong conclusions. To explore the effect of a traditional preservation procedure, we quantified the changes in body shape and size of the golden mojarra, Diapterus aureolus (Jordan et Gilbert, 1882), using geometric morphometrics. Materials and methods. Fish fresh samples were photographed and frozen for at least seven months. Then, they were set in 10% formaldehyde, and passed through a wash of tap water and submerged in 70% ethanol. After five months the samples were photographed again. The differences between the mean shapes of two data groups (fresh fish and fixed specimens) were calculated by using the Procrustes distance. Effects associated with preservation were visualized by comparing the mean shape from each group, using a thin plate spline. A canonical variate analysis was carried out to detect the degree of intraand inter-specific variation with D. brevirostris as an outgroup. Also, matrices of correct classification, based on Mahalanobis distances, were obtained. Results. Procrustes distance between the two data sets was statistically significant (P < 0.001), suggesting that the fixation process produces changes in body shape. Canonical Variate Analysis verified that there were significant differences among three groups (fresh D. aureolus, fixed D. aureolus, and D. brevirostris; P < 0.001 for both CV1 and CV2), which were correctly classified (98.9%). In spite of the significant differences detected between the fresh and fixed data sets, these were less than those found in the outgroup. The pooled data of all specimens belonging to D. aureolus (fresh and fixed) produced a definitive correct classification (100%) between D. aureolus and D. brevirostris, indicating that the differences caused by the preservation method is not enough to confound species and, consequently, taxonomic integrity was totally acceptable. Conclusion. Our results show a change in size and shape that are consistent with changes obtained with this and other methods applied to other species: generally shapes change and sizes tend to shrink with preservation of specimens. This is probably caused by dehydration from freezing and thawing, exposure to ethanol, and dissolution of skeletal structures caused by formaldehyde. While this effect was clear, it was not enough to confuse species. Caution is advised when working with groups with a close relation (populations or not clearly-defined species). We recommend a similar exercise with a case study with these levels of divergence.
The Croaking Gourami Trichopsis vittata (Cuvier, 1831) is a native fish to southeastern Asia and Sundaland, with introduction reports from the USA, Philippines, and many other countries including India. In India, this species was first reported from Chembarampakkam Lake situated in Chennai during the year 2015. This study reports the presence of this fish for the first time in the Magra Beel, a wetland in the district of Nadia, West Bengal, in 2021, 2022, 2023. The laboratory evaluated the fish samples taken from the marsh to determine their fin ray counts and morphometric data. The results identified the species as T. vittata and supported previous research.
Museum fluid collections preserve important biological specimens for study. Tissues are often fixed in 10% buffered formalin to halt metabolic activities and transferred to a solution of ethanol for long‐term storage. This process, however, forces water from the tissues and has been shown to alter the morphology of preserved specimens in ways that may influence the biological interpretation of results. The degree to which fluid preservation alters morphology is linked to multiple biological factors, such as tissue size and composition, and should therefore be examined prior to functional analysis. This study is undertaken as part of a more inclusive examination of mammalian volar morphology. A sample of five adult male and five adult female rats (Rattus norvegicus) was utilized to evaluate longitudinal changes in the dimensions of the volar pads across fixation in 10% buffered formalin and preservation in 70% ethanol for 1 year. No significant changes to the measured dimensions of the rat volar pads were present across stages of fixation and preservation, and no significant interactions of specimen size or sex were noted. These findings indicate that small mammalian volar pads that have been fixed in 10% buffered formalin and stored in 70% ethanol are appropriate for morphological study using the measurements described here without corrective algorithms. This finding is rare among preservation studies but highlights the variability of tissue behavior during chemical preservation and the necessity of preliminary investigations of preservation artifacts. Concurrence here between the preserved and unpreserved samples is likely related to the anhydrous nature of the volar pads and the supporting skeletal structure, and their confined position between major joints of the hands and feet.
The striped snakehead Channa striata is a freshwater fish with potential for aquaculture for consumption and as a source of nutraceutical products. A domestication program using seed (wild fry) from Sigi District in Central Sulawesi Province was initiated in 2013 to promote snakehead culture (grow-out and full-cycle) in this province. During the first two stages (fry to fingerling, fingerling to juvenile), cannibalism was the only observed cause of mortality. The main aim of the third stage was to evaluate locally available natural feeds for juvenile snakeheads over 180 mm in total length. Juvenile snakeheads were reared for 8 weeks in individual compartments in a concrete tank with 3 natural feed treatments (A: Golden apple snail, Pomacea canaliculata; B: Blue panchax, Aplocheilus panchax; C: Earth worms, Lumbricus rubellus) and 5 replicates per treatment. Feeding (11% of body weight) was twice daily. All juveniles remained in good health, however results showed that treatment B produced the highest relative growth in wet weight (21.8%), significantly different from A (11.8%) and C (9.5%). Over the 3-stage study period the length-weight relationship W = aLb was isometric (b=3), with considerable variation in individual growth patterns.
The striped snakehead or snakehead murrel (Channa striata) is a valuable food fish with a wide distribution in Asia, including Central Sulawesi. Data on C. striata resources in Central Sulawesi are extremely limited. Culture of this species is well advanced in India but as yet undeveloped in Indonesia and in particular in Central Sulawesi. A program was initiated in early 2013 to collect data on C. striata populations in two Districts (Sigi and Morowali Utara). Grow-out trials were also undertaken with seed and/or broodstock from these wild stocks. A field survey in Morowali identified several stocks, however from a bio-ecological point of view, there were indications that all were under pressure from fishing and environmental degradation. There were strong indications of declines abundance and average as well as maximum size. Early domestication efforts with seed from Sigi were successful in rearing fry (total length TL±SD 43.9±3.3mm; weight W±SD 0.78±2g) for a period of 70 days. The three feed regimes (treatments) used for the grow-out trials in concrete tanks were A: mosquito larvae; B: commercial feed; and C: a combination of both. There were 3 replicates of each treatment with 10 fish per unit (N=90). At both 30 and 70 days, both A and C were significantly different (F>F crit,α=0.01) from treatment B which produced the lowest biomass and average individual growth. For the first 30 days there was no significant difference between A and C, while after 70 days C produced the highest biomass, while A was significantly different from C (F>F crit,α=0.05) for biomass. Survival rate of B was significantly lower than C (100%) at both 30 and 70 days (F>F crit,α=0.01). Survival rate of A was not significantly different from B or C at 30 days but was significantly different from both (F>F crit,α=0.05) at 70 days. Cannibalism was the main cause of mortality in A and B, and occurred whenever there was a substantial difference in size. It was concluded that mosquito larvae are one live feed which is suitable for young C. striata fry, but fingerlings of around 60mm TL require additional nutrition which can be supplied by commercial feed. However the commercial feed alone was unsuitable for C. striata fry and fingerlings. Regular grading based on size would be essential to prevent high levels of cannibalism. Analysis of length/weight data revealed an isometric growth pattern (W=aL b) with b=3 and a=0.000008255. The bioecological condition of wild habitats emphasizes the urgency of striped snakehead domestication and the conservation of C. striata resources in Central Sulawesi to enable sustainable use of this species.
Abstrak. Ikan gabus (Channa striata) merupakan ikan konsumsi bernilai ekonomis tinggi dengan distribusi luas di Asia, termasuk di Sulawesi Tengah. Data mengenai sumberdaya C. striata di Sulawesi Tengah sangat terbatas. Budidaya jenis ikan ini telah cukup maju di India namun belum berkembang di Indonesia termasuk di Sulawesi Tengah. Program penelitian ini dimulai pada awal tahun 2013 bertujuan menginventarisasi populasi C. striata di dua Kabupaten (Sigi dan Morowali Utara) di Provinsi Sulawesi Tengah. Disamping itu dilakukan pula upaya pembesaran ikan gabus dengan menggunakan benih dan/atau broodstock berasal dari alam. Hasil survei lapang di Kabupaten Morowali berhasil diidentifikasi sejumlah stok, namun dari aspek bioekologi semuanya terindikasi mengalami tekanan dari pemanfaatan (perikanan) dan degradasi lingkungan. Terdapat indikasi kuat terjadinya penurunan dalam kelimpahan maupun ukuran rata-rata dan ukuran maksimum. Upaya domestikasi awal dengan benih berasal dari Kabupaten Sigi (panjang total awal TL±SD 43.9±3.3 mm; berat awal W±SD 0.78±2 g) selama pemeliharaan 70 hari dinilai berhasil. Tiga perlakuan pakan yang digunakan dalam upaya pembesaran di wadah terkontrol (bak beton) adalah A: jentik nyamuk; B: pakan komersil; dan C: campuran keduanya. Untuk setiap perlakuan digunakan 3 ulangan dengan 10 ekor ikan per unit percobaan (N=90). Pada waktu pemeliharaan 30 and 70 hari, perlakuan A maupun C berbeda sangat nyata (F>F crit,α=0.01) dengan perlakuan B yang menghasilkan biomassa dan pertumbuhan rata-rata
The striped snakehead Channa striata is a freshwater fish with potential for aquaculture for consumption and as a source of nutraceutical products. A domestication program using seed (wild fry) from Sigi District in Central Sulawesi Province was initiated in 2013 to promote snakehead culture (grow-out and full-cycle) in this province. During the first two stages (fry to fingerling, fingerling to juvenile), cannibalism was the only observed cause of mortality. The main aim of the third stage was to evaluate locally available natural feeds for juvenile snakeheads over 180 mm in total length. Juvenile snakeheads were reared for 8 weeks in individual compartments in a concrete tank with 3 natural feed treatments (A: Golden apple snail, Pomacea canaliculata; B: Blue panchax, Aplocheilus panchax; C: Earth worms, Lumbricus rubellus) and 5 replicates per treatment. Feeding (11% of body weight) was twice daily. All juveniles remained in good health, however results showed that treatment B produced the highest relative growth in wet weight (21.8%), significantly different from A (11.8%) and C (9.5%). Over the 3-stage study period the length-weight relationship W = aL b was isometric (b=3), with considerable variation in individual growth patterns.
Length–weight relationships of six fish species are presented. Fish samples were collected from the Lancang River, in the Chinese section of the Upper Mekong River, in southwestern China. This study reports the first length–weight relationship for one of these species.
This research developed a computer system capable of recognizing some fish images. The system known as the "shape- and texture-based fish image recognition system" (FIRS) consists of five subsystems-namely: 1) image acquisition, 2) image preprocessing 3) feature extraction, 4) image recognition and 5) result presentation. The experiment was conducted on 30 fish species, which consisted of 600 fish images as the training dataset and 300 fish images for testing. The system compared two recognition techniques-a Euclidean distance method (EDM) and artificial neural networks (ANN). The system was able to recognize all 30 species of the training fish images with a precision of 99.00 and 81.67% for the ANN and the EDM techniques, respectively. The average access times were 24.4 and 154.43 sec per image for the EDM and ANN techniques, respectively.
This work aims to quantify the variation in total length and body mass for the early-juvenile Brazilian herring Sardinella janeiro and to determine total length and body mass correction equation to allow fresh measures to be calculated from preserved ones. Fishes were randomly assigned to one of five preservation methods (freezing at - 20º C, 2.5% and 5% formalin, 70% and 95% ethanol), and measured for total length (TL) and body mass (W) before preservation, and on days 5, 15, 30, and 60 after storage. Significant reductions in total length and body mass occurred during the first 5 days after preservation and continued to contract significantly at a lesser rate through 30 days in most methods. Exceptions were shown for body mass in freezing and 5% formalin, where the greatest losses occurred after 30 days of preservation. The degree of shrinkage for total length and body mass was very much dependent on fish size, with smaller specimens shrinking more than larger ones. The fresh total length and body mass can be back-calculated using equations that describe the relationship between fresh and preserved individuals after 60 days storage for all methods except for body mass in freezing.
The relationship between condition and latitude, temperature, and sex of northern pike (Esox lucius) was examined by regression analysis of 5210 published observations drawn from more than 38 populations. Most populations showed nearly isometric growth, but the overall exponent of the power function relationship between total body length and body weight was slightly less than 3 (p < 0.01). Multiple regression analysis showed that females weighed about 9% more than males of equal length, that body weight for fish of equal length increased about 5% for every 10° increase in north latitude and increased about 4% for every 10 °C decrease in mean annual air temperature, and that fish in European and Asian populations attained about 13% greater weight for a given length than their North American counterparts.
Cyprinids were sampled, by electrofishing, from 159 sites on small rivers in four major watersheds across central Thailand. Total abundance, estimated by the depletion method, varied directly with water velocity and, inversely with discharge while species richness varied inversely with habitat width and, directly with ambient oxygen and alkalinity. Numerical abundance of cyprinids was well above that for any of the other 27 families of fishes represented in the catches. Incidence of occurrence was high only for a few cyprinid species in each watershed with most species present in ≤10% of the sites. Across all sites, cyprinids represented approximately 35% of all species captured and were absent from only two sites. Species richness was highest in the Maeklong watershed. Canonical correspondence analysis identified five significant habitat variables, temperature, habitat width, discharge, ambient oxygen and alkalinity, and the extent to which each influenced the distribution of the 41 cyprinid species. The results are discussed in relation to environmental factors and ecological adaptations.
The effects on standard length of storing laboratory-reared larval herring (9–19 mm live length) in 4% buffered formaldehyde
or 70% buffered ethanol with and without simulated capture by towed net were assessed. Lengths during storage were considered
stable after 15 days for larvae placed directly in formaldehyde, and after 30 days for larvae placed directly into alcohol
or for larvae treated by net-capture simulation before storage. The following linear regressions described the relationships
between live length and the stored lengths of larvae after these times: for larvae stored directly in formaldehyde, L = 1.765 + 0.867 × X1 for larvae stored directly in alcohol, L = 0.564 + 0.971 × X1; for larvae subjected to net-capture simulation then stored in formaldehyde, L = 0.984 + 0.993 × X1; and for larvae subjected to net-capture simulation then stored in alcohol, L = 0.532 + 0.989 × X1 where L = live standard length and X1 = standard length after storage. The non-linear regression formula parameterized by Theilacker (Fish. Bull US, 78,685–692, 1980) for northern anchovy larvae provided a good fit to the data for herring larvae subjected to net-capture
simulation and then stored in formaldehyde. However, the model had to be re-parameterized to provide a good fit for larvae
stored in alcohol. The precision achieved in length measurements using a computer-aided measuring system is also discussed.
Silurids were sampled, by electrofishing, from 159 sites on small rivers in four major watersheds across central Thailand, Eastern, Chao Phraya, Peninsula and Maeklong. Total abundance, estimated by the depletion method, was low across all sites at under 3% of all fishes and varied directly with water velocity, dissolved oxygen, iron and pH and, inversely with turbidity. Species richness was highest in Maeklong watershed and, across all watersheds, varied directly with ambient oxygen, iron and pH and inversely with turbidity. Incidence of occurrence was not high for any species within any but the lightly sampled Eastern watershed and no species was captured across all watersheds. Canonical correspondence analysis was applied and identified three significant habitat variables, temperature, conductivity and ambient oxygen, and the extent to which each influenced the distribution of the 17 silurid species. The results are discussed in relation to environmental factors and ecology.
Summary The relationships of total length (TL), fork length (FL) and standard length (SL) are presented for four fish species and the relationships between TL and wet weight for 23 fish species from the Chi River in northeastern Thailand. All length–length relationships were linear (r2 > 0.95). Slope (b) of the length–weight relationships showed values between 2.5073 and 3.4896.
Length–weight relationships of fish are often used to estimate the biomass of length distributions or to obtain indices of condition. Although large-scale spatial trends are known to exist, it is often assumed that length–weight relationships do not vary significantly within stocks or between neighbouring stocks. The present study examined length–weight relationships of 1334 haddock (Melanogrammus aeglefinus) and 1186 whiting (Merlangius merlangus) collected on a groundfish survey in the waters around Ireland in 2004. Additionally, condition indices were estimated for individual fish and for length-frequency samples in order to summarise the length–weight relationships. The length–weight regression showed a significant area effect but no significant differences existed between the sexes. The condition indices showed a moderate spatial structure for both species: around 25% of the variability could be explained by the location of the samples, the rest of the variability was due to other sources. Length–weight relationships did not appear to vary significantly within stocks, however differences between stocks were significant. In the present case, a bias of up to 10% could occur in biomass estimates as a result of applying length–weight relationships of one stock to length data of a neighbouring stock.
Sockeye smolts, pink and chum fry, and pink and chum fingerlings (Oncorhynchus) were sequentially weighed and measured when alive and after death in water and after killing and storage in formalin up to 225 days. The fish shrank within 12 hours to 97% and by 30–40 days to 96% of live length. Further changes in length were not significant. These same relative changes were observed from fish of different sizes, and the values were not significantly different among groups preserved in formaldehyde solutions of fresh or sea water. In fresh water, fish gained weight while yet alive but under anaesthesia. In freshwater formalin, fish gained weight rapidly for 1 or 2 days, then lost weight at a decelerating rate to the time of last measurement. Fish killed and stored in salt water formalin lost weight for the first few days, then gained weight at a decelerating rate. Relative magnitudes and rates of change were inversely related to size of specimens contained in the sample. These changes had pronounced effects on relative condition factors which varied from 97 to 135% of live values depending upon size of fish, type of formalin and time in preservative.
Balitorids were collected, by electrofishing, from small rivers across central Thailand between October 2000 and March 2004. Total balitorid abundance for the 18 species averaged 3·8% of the cumulative total for all fishes. Balitorid species numbers and abundance varied directly with elevation to c. 400 m, substratum particle size and ambient silica concentration. Species numbers at stations were modest and few species were widely distributed. Species associations related significantly with elevation, temperature and ambient concentrations of dissolved oxygen and silica. Turbidity was also significant but probably an artefact. Habitat separation clearly occurs among some balitorids, particularly the less common species, and probably represents species-specific direct and indirect habitat effects. The more common balitorid species tended to occur in similar habitats where the significant factors approximated average values. For these species, coexistence is suggested to occur through food resource sharing possibly facilitated through adaptations. Balitorid distributions in low-order rivers are attributed to the direct and indirect influences of the environment on energy available for the performance of essential activities.
Estimates were made of the growth rates and proximate body composition of larval and metamorphosing P. marinus (L.) collected at various times of the year from Shelter Valley Creek, Lake Ontario. Analysis of length-frequency data indicates that the average duration of larval life was 6 years, with metamorphosis occurring predominantly in the length range above 13 cm. Increases in length were almost entirely restricted to the warmest months and did not take place during the final year of larval life. Three categories were thus recognized for the proximate analysis: ammocoetes <13 cm, ammocoetes > 13 cm and metamorphosing individuals. In ammocoetes <13 cm, seasonal differences were observed in the regression coefficients in the logarithmic relationships between wet weight and length and between each of water, lipid and ash and the wet weight. No such difference was found for the regressions between protein and wet weight. For a fixed length (9 cm), the wet weight varied only slightly during the year, although a small peak was seen in May. When considered on the basis of fixed weight (1 g), the relative amount of lipid deposited was greatest in May/July, coincident with a high diatom density. The water content followed an inverse pattern to that of lipid, while the protein and ash contents showed little seasonal variation and exhibited values lower than those normally found in teleosts. Throughout the last year of larval life, the animal stored a greater proportion of lipid, presumably to facilitate the energy demands of metamorphosis during which this food store underwent a marked reduction.
Two groups of 30 Sarotherodon mossambicus were weighed and measured when alive, after 5 days in 10% formalin, and after 5, 10, 15, 20, 25, 30 and 65 days in 37.5% isopropyl alcohol. Fish from two size classes were preserved and all fish initially increased slightly in length and increased greatly in weight. The greatest increases in length and weight were noted after 5 days in formalin solution. After 65 days in isopropyl alcohol, the length of the preserved fish decreased to approach the live length while the weight of the fish stabilized at a higher than live weight value. This study is the first report of slight length increases or no shrinkage in preserved fish. Comments on the use of standard correction factors for lengthweight studies of preserved fish are provided.
This study presents a historical review, a meta-analysis, and recommendations for users about weight–length relationships, condition factors and relative weight equations. The historical review traces the developments of the respective concepts. The meta-analysis explores 3929 weight–length relationships of the type W = aLb for 1773 species of fishes. It shows that 82% of the variance in a plot of log a over b can be explained by allometric versus isometric growth patterns and by different body shapes of the respective species. Across species median b = 3.03 is significantly larger than 3.0, thus indicating a tendency towards slightly positive-allometric growth (increase in relative body thickness or plumpness) in most fishes. The expected range of 2.5 < b < 3.5 is confirmed. Mean estimates of b outside this range are often based on only one or two weight–length relationships per species. However, true cases of strong allometric growth do exist and three examples are given. Within species, a plot of log a vs b can be used to detect outliers in weight–length relationships. An equation to calculate mean condition factors from weight–length relationships is given as Kmean = 100aLb−3. Relative weight Wrm = 100W/(amLbm) can be used for comparing the condition of individuals across populations, where am is the geometric mean of a and bm is the mean of b across all available weight–length relationships for a given species. Twelve recommendations for proper use and presentation of weight–length relationships, condition factors and relative weight are given.
The weight-length (W-L) relation was estimated for an endemic catfish, Horabagrus brachysoma (known also as Asian sun catfish, Gunther's catfish, Manjaletta, or Manjakoori). The fish were collected from the four major river systems of Kerala, part of the Western Ghats Mountain range, between January 2005 and February 2006. The estimates for the parameter b of the W-L relation (W = aL(b)) ranged between 2.7623 and 3.17968. Linear regressions on log- transformed data were highly significant (P < 0.01) for the species in all the riverine habitats studied. Analysis of covariance revealed significant difference between sexes of H. brachysoma in the Chalakudy River for the slopes of the regression line.
FishBase (www Database) World Wide Web electronic publication
- R Froese
- D Pauly
Froese, R.; Pauly, D. (Eds.), 2010: FishBase (www Database) World Wide Web electronic publication. URL: http://www.fishbase.org. (accessed on May 2010).
Siluriform fishes and their habitat in small rivers in central Thailand
- Beamish