(a) (b) (c)
FIGURE 3: Linear measurements used for the estimation of focal index (Fi), (a) length of scale (LS). (b) Width of scale (WS). (c) Anterior focus length (AFL).
Results
Scale morphology and microstructural design
The general morphology of scales from the two selected regions is shown in figure 4. The scales of the studied cyprinid fish were cycloid, lacking ctenii on the posterior part. Each scale had a focus, dividing it into anterior, posterior, and lateral fields. The anterior field was embedded in the skin and overlapped by the next scale’s posterior side. The ventral part was shiny and smooth, while the dorsal part was rough and convex. From the focus, circuli (growth lines) emerge, densely packed in the anterior part and more widely spaced in the posterior part. The scales feature three types of radii: primary radii extending from the focus to the margin, secondary radii not reaching the margin, and tertiary radii extending from midway to the margin. Lateral line scales have a canal along the anterior-posterior axis with distinct openings.
(a)
(b)
FIGURE 4: Morphological characteristics of the fish scale used in this study.
(a) Key scale (b) Lateral line scale.
Scale type
Cycloid type of scale was shown by Schizothorax plagiostomus due to absence of any ctenii on its posterior region (Figure 5a).
Scale shape
Polygonal and cordate shaped scales were found in the studiedSchizothorax species. The rostral margin or front edges of the scales were often smooth, rounded and occasionally wavy (Figure 5b-c).
Focus
A clear focus, rounded in shape, was present (Figure 5d-f). The area enclosed by the focus was smooth. The mean value of size of focus was 122.90 μm (Table 1). It can be concluded that the position of focus in this species was antero-central as the mean value of focal index was 0.316 (Table 1).
Circulus/ circuli
The circuli were distinct and discontinuous and arranged in circular patterns (Figure 5g-i). In the anterior field, the circuli were closely spaced with mean value of intercircular space of 14.91 μm (Table 1). The mean value of number of circulii were 24 (Table 1) in the anterior field. There was an almost equal number of circuli in the transitional area between the anterior and posterior fields, while their number decreases in the posterior field. The shape of circuli was convex. Smooth circuli were present in this species due to the absence of lepidonts on circuli.
Radius/radii
Scales possess radii in nearly all four fields (anterior, posterior, and laterals) and was thus categorized as tetra-sectioned type (Figure 5j-l). The radii extending towards the posterior were longer compared to the others. Generally, the scales exhibited three types of radii: primary, secondary, and tertiary with primary radii being more numerous than secondary and tertiary ones. All radii were oriented parallel to each other, with a well-aligned arrangement in the posterior field .The average number of radii were 11 and the width of radii was 9.70μm in the anterior field (Table 1).
Lateral line scale
Lateral line scales in Schizothoracids included four parts viz. anterior, posterior and two lateral regions. The focus on these scales was absent and instead they have a channel existing along the anterior-posterior axis of the scales with two openings: anterior opening and posterior opening (Figure 5m-n). The mean value of length of lateral line canal was 1.52 mm and size of anterior opening of lateral line canal was 354.61 μm (Table 1).