Length-weight Regressions Research Articles

Length-weight relationships for five cladoceran species in an Amazonian lake

This work shows the length-weight regressions established for the five most frequent and abundant cladoceran species (Bosmina hagmanni, Bosminopsis deitersi, Ceriodaphnia cornuta, Diaphanosoma birgei, and Moina minuta) in two stations at Lake Batata. This lake has received for 10 years very fine bauxite processing tailings, which is responsible for the thick layer over the natural sediment still observed in its western section (impacted station). The individuals were separated into size classes, the dry weight values were determined for each class and were used for establishing weight-length equations. Bosminopsis deitersi and Ceriodaphnia cornuta were the species showing the smallest size in the two sampled areas (0.152 to 0.322 mm) and Diaphanosoma birgei was the largest (0.284 to 0.722 mm). In the natural station, Moina minuta and Bosminopsis deitersi were the lightest species (0.174 to 0.334 and 0.074 to 0.278 µg, respectively) and in the impacted station, Bosmina hagmanni and Moina minuta were the lightest (0.248 to 1.555 and 0.210 to 0.566 µg, respectively). In general, individuals from the impacted station exhibited smaller body sizes (0.152- 0.684 mm) and higher weight (0.208 - 1.983 mm), which can be explained by the ingestion of tailing particles. The equations established were shown to be adequate for weight estimates of the analyzed species since the differences found between the observed and estimated weights values were not statistically significant.

A preliminary investigation into the fisheries potentials of Doma Lake, Nasarawa State, Nigeria

A preliminary investigation into the fisheries potentials of Doma Lake in Nasarawa State, Nigeria was carried out from July to December 2000. Values of physico-chemical parameters (temperature, pH, dissolved oxygen, total alkalinity and free carbon dioxide) did not vary significantly (P > 0.05) between the sampling months. A total of 8 families made up of 11 genera and 16 species of fish were recorded in the lake. The family Cichlidae (67.56%) dominated while the family Hepsetidae was the least (0.45%). Length-weight regression analysis showed that six species of fish (Gnathonemus niger, Channa obscura, Hepsetus odoe, Oreochromis niloticus, Tilapia monodi and Tilapia zilli) exhibited positive allometric growth. Barilius niloticus showed negative allometric growth while Hemichromis bimaculatus showed isometric growth pattern. The mean standard length and weights of most of the species of fish correlated strongly except that of Barilius niloticus, which correlated weakly. The condition factor (K) showed that the smaller sized fishes thrived better in the lake. There were more male than female fish in the lake. Gnathonemus niger exhibited the highest fecundity while the lowest fecundity was observed in Hemichromis fasciatus and Tilapia zilli. The implications of the findings are discussed. Key Words: Fisheries potentials, Doma Lake, Nigeria Journal of Aquatic Sciences Vol.19(2) 2004: 59-64

Is weight an important parameter when measuring copepod growth?

We studied in situ weight increment of Calanus helgolandicus developing under field conditions. Weight increment between successive stages was rather similar for early nauplii (NII–NV ∼2.00 μgC μgC −1) and for early copepodites (NVI–CIII mean: ∼2.40 μgC μgC −1) but lower for late copepodites (CIV ∼0.80 and CV ∼0.20 μgC μgC −1). Weight increment of CIV and particularly CV was found to be closely linked to the method used to estimate the weight: either (i) directly measured weights, or (ii) weights estimated from a length–weight regression. The weight of CV, which has a relatively long stage duration, shows wide variations within the stage while length variations within stage are very low. For example, on the 17th of August, some CV had a carbon weight three times higher than other ones. The main cause of variation is the age of the individuals within the stage. We recommend direct weight measurement rather than the use of length–weight regression to estimate weight increment. However, and especially for stages with large variations in weight, whether the individuals are at the mid-point of their stage should be checked.

Modelling the effects of different quality prey fish species and of food supply reduction on growth performance of Roseate Tern chicks

We assessed the effects of different quality fish species and reductions in their abundance in the growth of Roseate Tern ( Sterna dougallii) chicks in the Azores. An energetic balance model was developed, which accounts for the energy available from ingested fishes and the energy expenditure by the chicks. Fish species ingested by Roseate Tern chicks were mainly Trachurus picturatus, Scomberesox saurus, Macroramphosus scolopax and Capros aper. Energy expenditure was defined by the basal metabolic rate (BMR), which depends on chick’s weight, plus a multiple of BMR, obtained by calibration and accounting for unspecified energetic losses. Real data obtained in June–July of 1996 and 1995 were used to calibrate and validate the model, respectively. Regressions between observed and predicted data showed a higher fitting level for 1996 than for 1995, which seems to be related with the need for more accurate estimations of assimilation efficiency and energy expenditure parameters. Of the four main prey species, T. picturatus was the most energetically favourable because of its high length–weight regression and to the capacity of chicks to swallow T. picturatus with an average length of 8.71 cm. C. aper had a higher length–weight relationship, but chicks were only able to ingest items <5 cm because this species is wider than T. picturatus. S. saurus and M. scolopax were energetically less efficient because they had a lower length–weight relationship. Observations suggest that the availability of less energetic fish (e.g. M. scolopax) leads to higher delivery rates by the parents and, consequently, to higher ingestion rates by the chicks. However, both observations and predictions suggest that the growth efficiency is lower than when the chicks were fed with T. picturatus with an average length of 8.71 cm. Additionally, the model predicts that chicks with 23 days of age will attain 85 and 56 g, according to a 25% reduction in prey within a year of energetically more and less favourable prey, respectively. Chicks in the first situation are still likely to fledge, while in the second case, chick survival is certainly compromised. In summary, the growth of Roseate Tern chicks in the Azores will be significantly reduced in response to a decrease in energy intake resulting from provisioning of low quality fish species and chick survival is compromised whenever this factor is associated with a significant (25%) reduction in fish stocks. This model proved to be a highly dynamic tool in assessing variations in postnatal growth of Roseate Terns in response to variations in food quality and quantity and it should be of interest in the conservation strategy of this species.

Growth and length-weight relationship of the juvenile anchovy, Engraulis encrasicolus, in the nursery ground (Zrmanja River estuary-eastern Adriatic Sea)

Growth and length–weight relationships of 2564 juvenile specimens of anchovy, Engraulis encrasicolus (Linnaeus, 1758), were examined over a 2-year period (August 1989 to April 1991) in the Zrmanja River estuary. Fish sizes ranged from 4.4 to 12.5 cm total length and 0.5 and 13.8 g, corresponding to age (in years) 0+ (98%) and 1+ (2%). Length–weight regression coefficient (b) varied between 2.95 and 3.42 and the regression constant (a) between 2.1 and 6.0 (×10−3). The von Bertalanffy growth equation of juvenile anchovy was: lt = 13.2 (1 − e−0.82(t+0.5)). Maturity was reached in June in males above 8.2 cm and females above 9.0 cm total length.

Age, growth and mortality of picarel, Spicara smaris L. (Pisces: Centracanthidae), from the eastern Adriatic (Croatian coast)

Age, growth and mortality of picarel Spicara smaris L. collected in the eastern middle Adriatic during April and May in 1999 were studied. The total lengths of individuals ranged from 6.3 to 19.8 cm, and the weight from 2.2 to 78.3 g. The slopes (b values) of the total length-weight regressions indicated negative allometric growth for females (b = 2.8+/- 0.03) and isometric growth for males (b = 3.08+/-0.04). The oldest female and male were 4 and 6 years, respectively. The von Bertalanffy growth parameters for the sexes combined were (L-infinity = 22.76 cm, K = 0.277, t(0) = -0.793). The overall sex ratio was 1 : 4.1 in favour of females. Individuals larger than 17.9 cm were all males.

Intrabasin variations in age and growth of Barbus bocagei populations

The age and growth of the Iberian cyprinid Barbus bocagei Steindachner 1865, were studied in six different streams in the River Tagus basin. The fish were aged by scale reading and their lengths were back-calculated. Age structures were similar at four sites (R. Ocreza, R. Rio Frio, R. Sever and R. Canha), where six to seven age classes were present. In contrast, 10 age groups were detected in the R. Erges and 11 in the R. Nabao. The slopes (b) of the length–weight regressions did not differ significantly between the six populations. The growth of the populations was compared with that available throughout the study area (another two sites). Classification analysis of the lengths-at-age by sites matrix revealed three major groups (by decreasing order of growth rate): 1, Belver Reservoir; 2, R. Tagus, Nabao and Erges; 3, Rio Frio, Sever, Canha and Ocreza. We hypothesize that highly stressful conditions in the summer diminish growth rates and longevity in the Rio Frio, Canha and Ocreza rivers and that lower temperatures all year round could limit growth in the Sever. Higher growth rates were observed in warm-water streams with more stable environmental conditions (group 2) and in a highly productive lentic system (group 1). Among the sites that were studied, the one that revealed the highest growth performance by B. bocagei was the most polluted, the R. Nabao. This offers evidence of the species plasticity and of its successful adaptation to streams displaying significant degradation in water quality.

Growth and reproduction of largemouth bass ( Micropterus salmoides Lacépède, 1802) in Lake Trasimeno (Umbria, Italy)

Growth and reproductive biology of largemouth bass was investigated to study aspects of its biology as well as possible effects upon other fish species as a result of its introduction to Lake Trasimeno. From April 1993 to May 1994, 182 specimens (87 males, 83 females, 12 sexually indeterminate) distributed among seven age classes were captured. The length–weight regression was W=0.00988LT 3.1512±0.027 (males) and W=0.00888LT 3.184±0.032 (females) without any significant differences between sexes. The growth of the 1+age-class is not continuous throughout the year; it slows to almost nothing in the winter. The parameters of the von Bertalanffy growth curve for length were L ∞=46.88, K=0.33 and t 0=0.056 for the females and L ∞=39.4, K=0.42 and t 0=0.019 for the males. The condition factor indicates that the Lake Trasimeno population is in excellent condition. Reproduction occurs mostly in May. Sexual maturity is reached at 2 years for males and 3 years for females, at lengths and weights of 22 cm and 160 g for males and 30 cm and 397 g for females, respectively. Largemouth bass has adapted well to Lake Trasimeno where physical and trophic conditions favour growth and reproduction.

Food and condition of the catfish &lt;i&gt;Synodontis&lt;/i&gt; in Upper Benue River Basin, Yola Area, Nigeria

Investigation was carried out on food and condition of the Catfish, Synodontis species in the Upper Benue River Basin, Nigeria from March to June, 2000. Fish samples were obtained twice monthly from different fish landing sites. Analysis showed that there was no significant difference between the sizes of males and females. Length-weight regression analysis indicated isometric growth of the species sampled. Correlation analysis between length and weight was highly significant. Monthly mean condition factor was constant during the period of investigation. The fish species exhibited diversity in their diets with insect parts, larvae and Algae as the main diets. The overall sex ratio showed a close proximity to 1:1 ratio. Key words : Food, condition, Synodontis sp. Journal of Aquatic Sciences Vol.17(2) 2002: 105-108

Assessment of Tolerant Sunfish Populations (Lepomis sp.) Inhabiting Selenium-Laden Coal Ash Effluents: 1. Hematological and Population Level Assessment

Sunfish were collected from coal ash effluent-receiving streams and Ohio River watershed reference sites to assess the effects of exposure to low-level selenium concentrations. Selenium, copper, and arsenic concentrations were statistically higher in tissue samples from exposed fish than in reference fish. Leukopenia, lymphocytosis, and neutropenia were evident in exposed fish and were indicative of metal exposure and effect. White blood cell counts and percent lymphocyte values were significantly correlated with liver selenium concentrations. Plasma protein levels were significantly lower in exposed fish than in fish from the Ohio River, indicating that exposed fish may have been nutritionally stressed. Condition factors for fish from the ash pond-receiving streams were the same as, or lower than, those of fish from the reference sites. There was no evidence that the growth rate of fish in the receiving streams differed from that of fish in the reference streams. Despite liver selenium concentrations which exceeded reported toxicity thresholds and evidence of significant hematological changes, there were no significant differences in fish condition factors, liver–somatic indices, or length–weight regressions related to selenium.

Length–weight relationships for 18 Lessepsian (Red Sea) immigrant fish species from the eastern Mediterranean coast of Turkey

Length–weight relationships were estimated for 18 Red Sea immigrant fish species from the eastern Mediterranean coasts of Turkey. The values of the exponent b in the length–weight regression (W= aLb) ranged between 2·482 and 3·355. The median value was 3·018 and 50% of the values ranged between 2·835 and 3·121.

In situ versus laboratory estimations of length–weight regression and growth rate of Daphnia magna (Branchiopoda, Anomopoda) from an aerated waste stabilization pond

The present paper questions the adequacy of using length–weight regressions and growth rates calculated in the laboratory under constant physico-chemical and food conditions for the estimation of biomass and secondary production of animals living in a variable environment from the physico-chemistry and food availability point of view. Length–weight regressions (LWR) and growth rate of Daphnia magna were determined in situat five key periods of the year. In parallel, LWR and growth rate were determined in laboratory incubators at temperature adjusted to the mean temperature measured during the in situexperiments. LWR estimated from pond daphnids collected during the in situ experiments were, on the whole, not significantly different from LWR established during laboratory experiments, indicating that the food availability was globally similar in the laboratory and in situexperiments, even though food items were substantially different between the experiments. In situ algal biomass was indeed low compared to the algal biomass in laboratory experiments, but high biomasses of bacteria, protozoa and detritus were available for daphnid feeding in the tubes incubated in situ. Growth rate of D. magnawas monitored in situusing 50-ml tubes closed with Nylon net (mesh size = 80 μm) and in the laboratory using 50-ml glass flasks. The physico-chemical, bacteriological and algological variables were checked to be similar in the tubes and in the pond. Growth rates varied according to the size of the animal and according to the water temperature. The maximum growth rates were observed for juveniles at 20.2 °C. Growth rates were also determined in the laboratory at temperature corresponding to the mean temperature recorded in the pond during the in situ growth experiments. Differences between in situ and laboratory body length–growth rate regressions (LgR) were observed for the experiments conducted at 15.6 °C and 23.6 °C. Due to differences in LWR and LgR between in situ and laboratory experiments, biomass and daily production estimated from laboratory cultures were found to be significantly, but not severely, higher than biomass and daily production estimated on the basis of in situ experiments. It has been, therefore, concluded that, when the constraints linked to the realization of in situ growth experiments are too strong, the laboratory approach is fully justified.

Dry weight carbon and nitrogen content of some euphausiids from the north Atlantic Ocean and the Celtic Sea

Euphausiids were identified, measured and then dried during a research cruise to sites in the north-eastern Atlantic Ocean and shelf waters of the Celtic Sea in late summer. The lengths of furcilia larvae and later stages were measured in three ways, and regressions relating each pair of measures were calculated for different developmental stages of each species. Four hundred and ninety-three dried specimens of nine species were weighed and length-weight regressions were calcu- lated. A subset of 187 specimens was selected for analysis of carbon (C) and nitrogen (N) content soon after return to the laboratory. The C and N contents of a further 122 specimens were determined after the specimens had been stored for 9 years. No consistent differences in percentage C and N content were found between the two groups, indicating no systematic change during prolonged storage in desiccators. Calyptopes of Nyctiphanes couchi contained a lower percentage of both C (mean 36.2%) and N (mean 8.6%) than later stages (means: 40.6% C, 11.0% N). Carbon content and C:N ratios of a group of specimens of Thysanoessa longicaudata, including some juveniles, adult males and adult females, were distinctly higher (>46% and >5.0, respectively) than those of the majority of specimens of the same species.

Length-Weight Relationship and Relative Condition of Bundh and Hatchery-bred Labeo rohita (Ham) During the Early Period of Development

Length-weight relationship and relative condition factor for the early period of development of Labeo rohita (Ham) collected from hatchery and bundh and reared in experi­mental hoopnets have been calculated. The source wise difference in the exponent value 'b' was significant (P&lt;0.001) at 236 d.f. From the length-weight regression the exponent value 'b' was 3.125 for the hatchery and 3.306 for the bundh-bred species and these values from both sources were found to depart significantly (P&lt;0.001) at 118 d.f. from the conventional 'cubic law'. The correlation coefficient 'r' was found to be 0.998 for bundh and 0.997 for hatchery and was highly significant (P&lt;0.001). Low 'Kn' values of the species at 6.0 mm size, gradually increased upto 7.5 mm size may be related to the 'lag phase' period of the growth of the species. In the 8.0-35.0 mm size range, 'Kn' value stabilized above '1' prob­ably due to good fertility and food supply of the pond as well as the high feeding intensity of the fishes. The results are reported in the text.

Biological parameters of the saddlead bream Oblada melanura in the eastern Adriatic

Age, growth, sex ratio, and mortality were analysed for saddlead bream collected in the eastern Adriatic from June to August in 1993 and 1994. The slopes ( b values) of the total length–weight regressions, which differ significantly between sexes, indicate positive allometric growth for females ( b=3.123) and isometric growth for males ( b=3.017) ( N=5341). Fish aged 1–11 years were present in the samples ( N=1729). Growth in length for both sexes was expressed using the Bertalanffy equation, L t =34.13(1−exp(−0.208( t+0.750))). Females grew slower ( K=0.201) than males ( K=0.233). The overall ratio was 1:1.20 in favour of females ( P<0.05). Males were dominant in length classes 11.0–20.0 cm, females in length classes 21.0–33.0 cm. All individuals larger than 29.3 cm were female. Total and natural mortality were Z=1.08 years −1 and M=0.47 years −1. The exploitation rate, E=0.56, revealed a high fishing pressure on the stock in the studied area.

Length-Weight Relationship and Relative Condition of Hatchery- and Bundh-Bred Catla catla (Ham) Spawn During Development

The length-weight relationship and relative condition (Kn) of hatchery- and bundh-bred Indian major carp, Catla catla (Ham) during the early developmental period were studied. The correlation coefficient (,2) was found to be 0.9799 (bundh) and 0.9430 (hatchery). The source-wise difference in the exponent values 'b' were significant at the 1% level. From length-weight regression, the exponent 'b' was 3.284734 for the bundh- and 2.767123 for the hatchery-bred species. The regression coefficient of log weight on log length of C. cat/a of both sources was found to depart significantly at I% level from the conventional cubic law. Low Kn of the species at 5.5 mm increased gradually up to 8.0 mm size. In the 8.0-18.5 mm size range, the value of Kn stabilized above 1 indicating a good supply of food in the pond.

Vegetational succession - Mediated spatial heterogeneity in the environmental biology of Periophthalmus Barbaras (Gobiidae) in the estuarine swamps of Imo River, Nigeria

Some aspects of the environmental biology of the amphibious gobiid, Periophthalmus barbanis, were studied to evaluate the impacts on the fish of the aggressive successional replacement of the native mangroves (Rhizophora mangle, Rhizophora racemosa, Rhizophora harrizonii, Avicenia afticana, Laguncularia racemosa) by the alien nipa palm (Nypa fruticans) in the estuarine swamps of Imo River, Nigeria. The unimpacted biotope with mangroves was referred to as ‘mangrove swamp’ while the impacted biotope with nipa palm was designated ‘nipa swamp’. This vegetational succession resulted in decreases in the nipa swamp of the sizes of the fish, diet diversity, foraging performance, reproductive investment and length-weight regression coefficient. Mean and intrapopulational variability in hepatosomatic index increased in the nipa swamp. No significant spatial variation was evident in body condition albeit intrapopulational variability was higher in nipa swamp than mangrove swamp

Factors Influencing Retention of Visible Implant Tags by Westslope Cutthroat Trout Inhabiting Headwater Streams of Montana

Retention of visible implant (VI) tags by westslope cutthroat trout Oncorhynchus clarki lewisi inhabiting 20 reaches of 13 isolated headwater tributary drainages in Montana was evaluated during 1993 and 1994. In 1993, 2,071 VI tags were implanted in westslope cutthroat trout (100–324 mm fork length) and adipose fins were removed as a secondary mark to evaluate tag retention. Of 348 westslope cutthroat trout recaptured during the year they were tagged, 201 (58%) had retained their tags. Of 616 westslope cutthroat trout recaptured the year after tagging, 355 (58%) had retained their tags. Logistic regression analyses indicated that fish length was the most significant variable that positively influenced tag retention. Other significant variables were wetted width and channel gradient of the stream in which fish were tagged and quality of tag insertion (rated at time of tagging). Fish condition did not significantly improve deviance performance of logistic regression models that included fork length and tag insertion quality. Neither slopes nor intercepts of log10(length)–log10(weight) regressions were significantly different (P > 0.10) between fish that retained tags and fish that lost them. Fish condition was not significantly different (P > 0.951; analysis of covariance) between previously tagged and untagged westslope cutthroat trout after differences between drainages and years were accounted for. We found no significant differences in slopes (P > 0.50) or intercepts (P > 0.05) of log10(length)-log10(weight) regressions between previously tagged and untagged fish. However, for 11 drainages where comparisons could be made, we found significant differences (P < 0.05) in length-weight regression slopes between previously tagged and untagged fish for one drainage and in regression intercepts for an additional three drainages. Ninety-five percent of all tags were readable at recapture, A logistic regression model predicted that tag retention would be 75% or higher for westslope cutthroat trout 155 mm FL or larger if tag insertion quality was good. In spite of relatively poor tag retention (<75%) by smaller (<155 mm) westslope cutthroat trout, VI tags were a valuable tool to assess movements of those fish retaining tags.

Shell Morphometry and Tissue Condition ofAmblema plicata(Say, 1817) from the Upper Mississippi River

ABSTRACT We examined shell length-weight relationships and shell shape in the unionid Amblema plicata (Say, 1817) from Pool 10 through Pool 26 of the upper Mississippi River. There were differences in both the intercepts and slopes of the relationships between size and other measured characteristics among the various pools examined. There was a much greater degree of variability in the tissue related factors than in any of the shell factors. There were no apparent upstream-downstream trends in any of the dependent variables. We also found that the shell can contain a significant amount of organic material and the percentage of organic material varied considerably, particularly in larger mussels. This indicates the need to consider the shell in studies of the energy dynamics of unionids. Tissue condition varied with mussel size; larger mussels had proportionally lighter shells and thus higher condition indices than smaller mussels. Because of the significant intra- and inter-pool variability in shell and tissue parameters which we observed, we urge that biomass estimates based on shell length-weight regressions for this and other species should be based on empirical relationships observed for the particular population under study rather than from literature values.

Annual biomass and production of the oceanic copepod community off Discovery Bay, Jamaica

Monthly samples were collected in oceanic waters off Discovery Bay, Jamaica, in 60- and 200-m vertical hauls, using 200- and 64-μm mesh plankton nets, from June 1989 to July 1991. Length-weight regressions were derived for twelve genera of copepods (R2=0.79 to 0.97). For eight occasions spanning the study period, biomass estimates generated from these length-weight regressions differed by only 3% from direct weight determinations. The mean ash content of copepods was 7.1%, and the energy density was 20.8 kJ g-1 ash-free dry weight (AFDW). Mean annual biomass of the total copepod community in the upper 60 m was 1.83 mg AFDW m-3 (range 1.14 to 2.89 mg AFDW m-3), and for the 200-m water column was 0.96 mg AFDW m-3 (range 0.12 to 1.99 mg AFDW m-3). Estimates of generation times for five common taxa ranged from 16.1 to 33.4 d. None of the taxa investigated displayed isochronal development; in general, stage duration increased in later copepodite stages. Weight increments showed a significant decrease in later copepodite stages, but with strong reversal of the trend from stage 5 to adult female in most species. Daily specific growth rates also declined in later copepodite stages, and ranged from 1.49 d-1 in stage 1–2 Paracalanus/Clausocalanus spp. to 0.04 in stage 5-female of Oithona plumifera. Progressive food limitation of somatic copepodite growth and egg production is postulated. Naupliar production was 50.4 to 59.5% of copepodite production, and egg production was 35.1 to 27.7% of copepodite production in the 60-and 200-m water columns, respectively. Total annual copepod production, including copepodites, nauplii, eggs and exuviae, was 160 kJ m-2 yr-1 for the upper 60 m and 304 kJ m-2 yr-1 for the upper 200 m. Secondary production of the copepod community in oceanic waters off Discovery Bay approaches 50% of the corresponding value in tropical neritic waters.