The selection of suitable indices for the measurement and analysis of fish condition

Abstract

A survey of the studies published in two leading fisheries journals revealed that the analysis and measurement of condition, based on length-weight data, has been performed using a wide variety of indices and statistical procedures. Eight forms of index were identified which can be categorized into those which measure thecondition of individual fish, i.e. 'condition factors '.and those which measure the condition of subpopulations as a whole, i.e. regressions of log,,, weight on log,, length and the parameters of such regressions. Analysis of a test data set indicated that both the form of index and properties of the data set size can dictate the patterns of condition observed. The various indices were reviewed in terms of appropriateness, simplicity and statistical correctness. It was concluded that an index should be selected only after a detailed examination of both the underlying assumptions of the index and the properties of the data set.

Relação peso-comprimento de duas espécies de peixes em um rio intermitente no nordeste do Brasil

“…This means a greater investment in growth rather than in weight gain. A negative allometric growth has been attributed to young individuals (Nomura, 1975;Vazzoler, 1996;Carvalho et al, 2008), as is the case of the present study. None of the species showed significant statistical difference in condition factor between the seasons (t-test, t A.bimaculatus = 4.5; d.f.= 558.5; p=0.651, t A.fasciatus = 1.3; d.f.= 182.2; p=0.195).…”

“…Subse- quently, the confidence level (95% CL) for the b parameter was determined. The condition factor (K) was obtained by the expression K=W/L b (allometric condition factor), where b is estimated by LWR after logarithmic transformation and setting by the method of least squares (Bolger and Connolly, 1989). Significance of differences in K or fish size between species or seasons were tested using student's t-test (α=0.05) for equality of variances not assumed by the log-transformed data (Sheridan and Lyndall, 2001).…”

Female mate choice and male red coloration in a natural three-spined stickleback (Gasterosteus aculeatus) population

“…Before releasing the male at the same site, we measured his (standard) length and weight to calculate his condition factor, 100 x weight (g)/length (cm)* where b is the slope of the regression of log(weight) on logflength) (Bolger and Connolly, 1989). To distinguish neighboring males, we marked nearest neighbors by clipping the tip of the first and/or second dorsal spine.…”

Hematological parameters of Hoplias malabaricus (Characiformes: Erythrinidae) parasitized by Monogenea in lagoons in Pirassununga, Brazil

“…The analysis of Kn variations between populations and individuals may be used to demonstrate a biological characteristic, such as environmental quality and the availability of feeding resources (BOLGER;CONNOLLY, 1989), and also of the parasite species on their hosts in a natural environment (PAIVA et al, 2000a) or in confinement . In the host-parasite relationship, it is common to observe a negative correlation between Kn and levels of parasitism.…”