Salmo trutta, Linnaeus, 1758
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publication ID |
https://doi.org/ 10.1111/jfb.13772 |
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DOI |
https://doi.org/10.5281/zenodo.10946252 |
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persistent identifier |
https://treatment.plazi.org/id/03F187DC-FFCB-5151-FFF9-F96A8023E9B9 |
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treatment provided by |
Felipe |
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scientific name |
Salmo trutta |
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3 | RESULTS View in CoL
3.1 | Geometric morphometrics
The shape changes associated with the first three between-group principal components ( Figure 1 View FIGURE 1 (b)) cumulatively explained 76.9% of variance in the data ( Table 1 View TABLE 1 ). PC1 described enlargement of head height at length, whereas PC3 was most strongly associated with reduced head and body depth. PC2 was associated with dorso-ventral arching of the body and, as an artefact of positioning the flexible fish bodies for photographing, was removed mathematically before further analysis (see § 2.4.1). While individual loadings on PC1 described a progressive, age-related shape change from a larger to smaller head size ( Figure 2 View FIGURE 2 (a)), loadings on PC3 appeared to describe an increase in body depth of exercised as opposed to control groups in the later stages of the experiment ( Figure 2 View FIGURE 2 (a)). This was partly confirmed by the results from linear discriminant analysis (LDA): the coefficients from linear discriminants 1 and 2, cumulatively explaining 88.33% of variance in the data ( Table 1 View TABLE 1 ) were most strongly associated with PCs 1 and 3, respectively ( Table 2 View TABLE 2 ). LDA achieved 85.19% correct group classification and 62.96% cross-validated correct classification for treatment groups across weeks ( Figure 2 View FIGURE 2 (b) and Table 3 View TABLE 3 ). Between-group Mahalanobis distances and permutated T 2 tests ( Table S 2 View TABLE 2 in File S1) confirmed a clear group separation along the age axis (weeks under treatment), associated with a decrease in head height/depth relative to lateral body depth (LD1, PC1; Figure 2 View FIGURE 2 (b)). Although body depth appeared to be greater in the exercised as opposed to control groups towards the end of the experiment (LD2, PC3; Figure 2 View FIGURE 2 (b)), the difference between same-aged exercised and control groups was not statistically significant (p> 0.05; Table S 2 View TABLE 2 in File S1).
3.2 | Mass–length relationships and condition at length
A comparison of log mass-log length relationships for the exercised v. control cohorts did not reveal a significant difference in the slopes (F 1,43 = 0.21; p> 0.05) or intercepts dependent on treatment (F 1,43 = 0.65; p> 0.05). Cohort-specific regressions of M and L S with the C00 individuals (n = 6) as a common origin described a mass– length relationship in the form of M ¼ 0:0143 L 3:0242 for the exercised s cohort and M ¼ 0:0146 L 3:0044 for the control cohort ( Figure 3 View FIGURE 3 ). Theres fore, exercised individuals were slightly (albeit not significantly) heavier for their length as they grew larger (stronger positive deviation of b from the cubic 3) than control individuals. Consequently, condition-at-length, K, derived from the regression parameters for each cohort, differed across weeks (i.e., age; F 3,39 = 194.038, d.f. = 3, p <0.001) as well as treatments (F 1,39 = 864.99, d.f. = 1, p <0.001) ( Figure 4 View FIGURE 4 ). In addition, the pattern of variation in K across weeks differed between treatments as indicated by the statistically significant interaction term (F 3,39 = 85.803, d.f. = 3, p <0.001). Specifically, K was higher in exercised compared with control groups over the whole experimental period. Within treatments, K consistently increased for exercised individuals over the experimental period, while for control individuals, K only increased from week 4 to week 20, week 4 to week 32 and week 10 to week 32 ( Figure 4 View FIGURE 4 ).
3.3 | Caudal-fin size
A CF: L S 2 did not differ between treatments at 20 weeks (mean S.E.; exercised = 0.029 0.002, control = 0.028 0.002; t = 0.291, d. f. = 9.36, p> 0.05) or at 32 weeks (exercised = 0.024 0.001, control = 0.024 0.001; t = −0.147, d.f. = 8, p> 0.05) after treatment initiation. However, overall and irrespective of treatment, A CF: L S 2 ratios were significantly higher after 32 weeks compared with 20 weeks (Figure 5) since treatment initiation (20 weeks = 0.028 0.001, 32 weeks = 0.024 0.001; t = 2.999, d.f. = 14.778, p <0.01).
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