(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).