Repeatability of fin length measurements using digital image analysis, and studies of fin morphology and erosion as indicator of social interactions of cod
Year: 2012
Type: dissertation
Abstract: Fin damage, commonly termed as fin erosion, has been paid considerable attention as a worldwide welfare issue especially in cannibalistic fish species. As cannibalistic fish, Atlantic cod (Gadus morhua) has been showed to have fin damage. The present study was conducted with 2100 juvenile cod with a mean initial body weight of 34.6g. The lengths of four fins (three dorsal and the caudal) for each fish were measured, and the measurements were made by three different assessors at three different points of time (recording 1-3) within six weeks of the experiment. This paper demonstrates the application of digital image analysis for analyzing fin length of cod. In order to provide an indication of the repeatability of digital image analysis, a reliability test was performed. The image of 42 randomly chosen juvenile cod taken at recording 3 was analyzed repeatedly by three different assessors. Significant differences in fin length measurements were found both between and within assessors. However the Pearson’s correlation in fin length measurements between each of the two assessor replicates was equal to or higher than 0.45. There were moderate correlations of fin length measurements between different assessors (r=0.45-0.84), and the correlations between replicates within same assessor were strong (r=0.57-0.94). In addition, majority of the variance was found to be attributed to the fish effect rather than assessor effect. Generally there were moderate repeatability of the fin lengths analyzed using digital image (R=0.46-0.61). With the support of all the statistical results from the reliability test, it is justified to say that this digital image based approach to measure fin length is accurate and feasible for genetic analyses. \n\nAll the data set obtained from 2100 juvenile cod was used to assess the changes for all four fins during the experiment due to growth or possible erosion. “Relative fin length” expressed as the percentage of fin length to the total body length, was applied in this study to assess the fin erosion. All four fins of fish suffered damages within the first two weeks (recording 1-2), and the caudal fin showed the most injury. In the following four weeks until the end of the experiment (recording 2-3), the cannibalism diminished with anterior dorsal fin still suffering degeneration. Later the incidence of fin erosion also reduced compared to that described for the first two weeks of the experiment. In general, the damage was concentrated on anterior dorsal and caudal parts of the fish. A possible hypothesis is that the fin erosion was probably due to attacks among the cohorts in the same rearing unit for the establishment of dominance hierarchy (i.e., social interactions). More relevant research is however needed to understand the underlying reasons that may explain the observed fin damage.
Author: Yajing He
Language: English
Subfield: Water Science and Technology
Field: Environmental Science
Domain: Physical Sciences
SDG: Life below water
Open Access status: green
Funders: Norges Forskningsråd, Nofima
OpenAlex ID: W2470400015