Salmo trutta Linnaeus 1758
Creators: name: Fenkes, Miriam
name: Shiels, Holly A.
name: Nudds, Robert L.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Salmoniformes
Salmonidae
Salmo
Salmo trutta

description: 3 | RESULTS
3.1 | Geometric morphometrics
The shape changes associated with the first three between-group principal components (Figure 1 (b)) cumulatively explained 76.9% of variance in the data (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 (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 (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) were most strongly associated with PCs 1 and 3, respectively (Table 2). LDA achieved 85.19% correct group classification and 62.96% cross-validated correct classification for treatment groups across weeks (Figure 2 (b) and Table 3). Between-group Mahalanobis distances and permutated T 2 tests (Table S 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 (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 (b)), the difference between same-aged exercised and control groups was not statistically significant (p> 0.05; Table S 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). 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). 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).
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).
description: Published as part of Fenkes, Miriam, Shiels, Holly A. & Nudds, Robert L., 2018, Body shape and robustness response to water flow during development of brown trout Salmo trutta parr, pp. 360-369 in Journal of Fish Biology 93 (2) on page 364, DOI: 10.1111/jfb.13772, http://zenodo.org/record/10928744