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Comparative Study
. 2016 May 20:6:26308.
doi: 10.1038/srep26308.

Key role of scale morphology in flatfishes (Pleuronectiformes) in the ability to keep sand

Marlene Spinner  1 , Mareike Kortmann  1 , Camille Traini  2 , Stanislav N Gorb  1
Affiliations
Comparative Study

Key role of scale morphology in flatfishes (Pleuronectiformes) in the ability to keep sand

Marlene Spinner et al. Sci Rep. .

Abstract

Flatfishes bury themselves for camouflage and protection. Whereas species-specific preferences for certain sediments were previously shown, the role of scales in interaction with sediment has not been investigated. Here, scale morphology and sediment friction were examined in four European pleuronectiforms: Limanda limanda, Platichthys flesus, Pleuronectes platessa, and Solea solea. All species had different scale types ranging from cycloid to ctenoid scales. On the blind side, the number of scales is higher and scales have less ctenial spines than on the eye side. The critical angle of sediment sliding (static friction) significantly depended on the grain size and was considerably higher on the eye side. The effect of mucus was excluded by repeated measurements on resin replicas of the skin. Our results demonstrate the impact of scale morphology on sediment interaction and give an insight about the ability of scales to keep sand. Exposed scales and a higher number of ctenial spines on the eye side lead to an increase of friction forces, especially for sediments with a smaller grain size. Our results suggest that the evolution of scales was at least partly driven by their interactions with sediment which confirms the relevance of sediment for the distribution and radiation of Pleuronectiformes.

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Figures

Figure 1
Figure 1. Scale density of S. solea, P. flesus, L. limanda, and P. platessa.
Scale density on the dorsal (d) and ventral (v) part of the eye side (gray fish symbol) and blind side (white fish symbol). Standard deviation is presented by error bars. Brackets indicate significant differences (One-Way ANOVA, P ≤ 0.001; multiple comparison procedures Holm-Sidak method, P < 0.05).
Figure 2
Figure 2. Scanning electron micrographs of scales of Pleuronectiformes.
(A) Scales of the blind side of S. solea. (B) Scales of the eye side of S. solea. (C) Scales of the blind side of P. flesus. (D) Scales of the eye side of P. flesus. (E) Scales of the blind side of L. limanda. (F) Scales of the eye side of L. limanda. (G) Scales of the blind side of P. platessa. (H) Scales of the eye side of P. platessa.
Figure 3
Figure 3. Scanning electron micrographs of ctenial spines of scales of Pleurenectiformes.
(A) S. solea. (B) P. flesus. (C) L. limanda.
Figure 4
Figure 4. CSAs of the three sediment types (fine, medium, and coarse) in three directions: cranial (black bars), caudal (gray bars), and lateral (white bars) on the eye side (gray fish symbol) and blind side (white fish symbol).
(A) S. solea (B) P. flesus. (C) L. limanda. (D) P. platessa. Brackets indicate significant differences of CSAs of the different sliding directions (Kruskal-Wallis One-Way ANOVA on Ranks, P ≤ 0.001, Tukey test P < 0.05). Lines indicate significant differences between the eye side and the blind side (Mann-Whitney Rank Sum test: *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001). Standard deviation is presented by error bars. Triangles indicate measurements that were not normally distributed. Data are presented separately as box plots in the supplementary material (S2).
Figure 5
Figure 5. CSAs of the three sediment types (fine, medium, and coarse) in three directions: cranial, caudal, and lateral on skin of S. solea (black bars), P. flesus (hatched bars), L. limanda (white bars), and P. platessa (gray bars).
(A) Skin of the eye side. (B) Skin of the blind side. Brackets indicate significant differences of CSAs in different sliding directions (Kruskal-Wallis One-Way ANOVA on Ranks, 3 DF, P ≤ 0.001; Dunn´s method, P < 0.05). Standard deviation is presented by error bars.
Figure 6
Figure 6. Light microscopy images of replicas of flat fish skin.
(A) Ctenoid scale of the blind side of S. solea. (B) Tubercle scale of the eye side of P. flesus. (C) Ctenoid scale of the eye side of L. limanda.
Figure 7
Figure 7. CSAs of the three sediment types (fine, medium, and coarse) in three directions: cranial (black bars), caudal (gray bars), and lateral (white bars) on resin replicas of the eye side (gray fish symbol) and blind side (white fish symbol).
(A) S. solea. (B) P. flesus. (C) L. limanda. (D) P. platessa. Brackets indicate significant differences of CSAs of the different sliding directions (Kruskal-Wallis One-Way ANOVA on Ranks, P ≤ 0.001, Tukey test P < 0.05). Lines indicated significant differences between the eye side and the blind side (*P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001). Standard deviation is presented by error bars. Triangles indicate measurements that were not normally distributed. Data are presented separately as box plots in the supplementary material (S2).
Figure 8
Figure 8. CSAs of the three sediment types (fine, medium, and coarse) in three directions: cranial, caudal, and lateral on resin replicas of the skin S. solea (black bars), P. flesus (hatched bars), L. limanda (white bars), P. platessa (gray bars) and on a smooth resin surface (black lines).
(A) Replicas of the eye side. (B) Replicas of the blind side. Brackets indicates significant differences of CSAs of the different sliding directions (Kruskal-Wallis One-Way ANOVA on Ranks, P ≤ 0.001, Tukey test P < 0.05). Standard deviation is presented by error bars.
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References

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