Keywords
linear regression - otolith dimensions - shape indices
Introduction
Puntius sophore (Hamilton, 1822), commonly known as pool barb, stigma barb, and swamp barb, is a
freshwater to brackish-water fish belonging to the cypriniformes order and to the
cyprinidae family.[1] Cypriniformes are the largest group of fishes, with an estimated number of ∼ 3,500
species.[2] Puntius sophore is widely distributed in inland waters of Asia, including Bangladesh, Pakistan, India,
Nepal, Myanmar, Bhutan, Afghanistan, and China. This fish is benthopelagic (demersal),
inhabiting rivers, streams, and ponds of plains.[3] It is considered as a chief food source for poor people in Bangladesh,[4] and is used as an aquarium fish.[5] According to the red list (2010) of the International Union for Conservation of
Nature (IUCN), the status of this fish is regarded as of least concern.[6] However, studies from the Indian waters depicted that the fish is at lower risk
to near threatened in the Western Ghat and in the Harike wetland, due to heavy fishing
pressure.[7]
[8] Otoliths are paired calcified, aragonitic mineralizations located in the inner ear
of the fish, which contribute to audition and equilibrium.[9]
[10] Amongst the three otoliths, the sagitta is the largest, followed by the astericus
and by the lapillus.[11] The otolith continues to grow throughout the life of the fish, and its growth generally
follows an allometric increase with respect to fish size.[12] The variations in the shape of the sagitta otolith are immense and are species specific,
ranging from pinhead size to massive pieces of calcium carbonate (CaCO3).[11] Due to its interspecific variations and larger size, the sagitta otolith has been
used to estimate the taxon, age, size, migration, and feeding habits of fishes.[10]
[13]
[14]. Hence, knowledge of fish otolith morphometry is considered a valuable tool for
the identification of the stock,[15]
[16] population management,[17] determination of diet in predatory fishes,[18] ontogenic research,[19] ecomorphological studies,[20] and for the identification of specific species.[21]
Although the otolith chemistry of marine fishes has been extensively studied, information
on otolith of freshwater fishes concerning the Indian subcontinent is limited. Therefore,
the purpose of the present study was aimed to analyze the shape and morphometrics
measurements of the otolith of P. sophore.
Materials and Methods
A total of 41 specimens ranging between 66 and 109 mm in total length (TL) were procured
from the fish markets of the Faridabad (28.4211° N and 77.3078° E) and of the Yamunanagar
(30.133° N and 77.288° E) regions of Haryana, India, and brought to the laboratory
in an ice box. All of the fish specimens were cleaned and measured for TL, standard
length, HL, and body weight, nearest to 0.1 mm and 1 g, respectively. The sagitta
otoliths were removed by making a horizontal cut across the head of the fish. The
otoliths were cleaned manually by using 1% potassium hydroxide (KOH) solution to remove
otic fluid, blood, and tissue, and were air dried. The right and left otoliths were
kept separately in different labeled envelopes.
Digital images of both the right and left otoliths were obtained over a dark background
using a Magnus MSZ-TR stereo microscope (Magnus Analytics, New Delhi, India (fitted
with a Magcam DCS 5.1MP, ½.5′' CMOS SENSOR camera. Various morphometric measurements
of the otoliths,[22] as shown in [Table 1], were acquired using ProgRes CapturePro, version 2.80, software (Jenoptik AG, Jena,
Germany), in which the otolith length (OL) was the maximum distance from the rostrum
to the postrostrum, and the otolith width (OW) was the distance perpendicular to the
length passing through the dorsal and ventral rim ([Fig. 1]).
Fig. 1 Otolith of Puntius sophore (a) The distance between a and b is the otolith width, and the distance between c
and d is the otolith length, (b) various otolith morphometric measurements used for
the present study.
Table 1
Variables utilized to study otolith morphology[22]
|
Variables
|
Measurements
|
Description
|
|
Relative dorsal length, (D)
|
d-d'
|
|
|
Relative medial length, (M)
|
m-m'
|
|
|
Relative antirostrum height, (A)
|
m-a
|
|
|
Relative rostrum height, (R)
|
m-r
|
|
|
Relative antirostrum length, (AL)
|
al-d
|
|
|
Relative rostrum length, (RL)
|
rl-l
|
|
For the analysis of the shape of the otoliths, morphometric parameters such as OL,
OW, area (Ar) and perimeter (P) were utilized to calculate four dimensionless shape
indices (form factor (FF); circularity (C); rectangularity (REC); and aspect ratio
(AR)[23]
[24] ([Table 2]). Form factor is a mean to estimate the surface area irregularity, C gives information
on the similarity of various features to a perfect circle, REC describes the variations
of length and width with respect to the area, and AR expresses the shape tendency
of the otolith.[23] To statistically analyze the data, SPSS for Windows, Version 16.0 (SPSS Inc, Chicago,
IL, USA) and Microsoft Excel, version 2007 (Microsoft Corp., Redmond, WA, USA) were
employed. The difference between the OL and the OW of the right and left otoliths
was examined by employing the independent t-test. The relationship between the TL and the HL of the fish and the OL and OW was
described by a linear equation.
Table 2
Shape indices calculated using otolith morphometric parameters[23]
[24]
|
Parameters
|
Shape indices
|
Formulae
|
|
Area (Ar)
|
Aspect ratio (AR)
|
OL/OW
|
|
Perimeter (P)
|
Form factor (FF)
|
4ԉAr/P2
|
|
Otolith length (OL)
|
Rectangularity (REC)
|
Ar/OL/OW
|
|
Otolith width (OW)
|
Circularity (C)
|
P2/Ar
|
Results
A total of 82 otolith samples were collected from 41 specimens. The OLs and OWs ranged
between 0.54 and 1.07 mm, and between 0.61 and 0.98 mm, respectively. Various morphometric
parameters of the fish were taken into consideration ([Table 3)]. The measurements of Otolith length (OL) and otolith width (OW) of both right and
left otoliths were tested and no statistically significant difference was observed
(p > 0.05). Therefore, either the left or right sagitta otolith can be used for the analysis.
For the present study, the left sagitta otolith was utilized. The shape of the otolith
of P. sophore was described as rectangular and less elongated, possessing well-defined antirostrum
and rostrum. The antirostrum was observed as short and narrow, with average height
and length of 28.8 ± 1.68 and 8.51 ± 0.6 0mm, respectively, whereas the rostrum was
noticed to be wide and round with a mean height and length of 55.4 ± 2.05 and 14.3 ± 1.25 mm,
respectively ([Table 4]). The otolith has smooth dorsal and ventral margins with an obtuse excisural notch.
The sulcus was found to be round and deep ([Fig. 2b]). By comparing the mean values of 4 shape indices of the otolith of P. sophore ([Table 5]), it was concluded that the average value of REC was the highest, while the value
of AR was the lowest (AR: 0.82 < C: 1.36 < FF: 31.91 < REC: 34.03). Furthermore, the
OL was found to be positively correlated with the AR, whereas the FF was found to
be negatively correlated with REC and C. The present study explains the relationship
between the TL and the HL of the fish with the OL and the OW described by the linear
equations y = 0.0052x + 0.309 ([Fig. 3a]); y = 0.0095x + 0.1114 ([Fig. 3b]); y = 7.2851x + 9.5285 ([Fig. 3c]), respectively. The results depicted that the OL and the OW were linearly correlated
to the TL and to the HL of the fish. The OW was found to be a better parameter in
estimating fish length than the OL.
Table 3
Mean, standard deviation, standard error, minimum and maximum values of various body
measurements of Puntius sophore
|
Parameter
|
Mean
|
SD
|
SE
|
Min
|
Max
|
|
Total length (TL)
|
83.9
|
10.4
|
1.6
|
66
|
109
|
|
Standard length (SL)
|
67.5
|
8.6
|
1.3
|
52
|
89
|
|
Head length (HL)
|
15
|
2.1
|
0.3
|
12
|
20
|
|
Body weight (BW)
|
104
|
36.9
|
5.8
|
40
|
210
|
Abbreviations: Max, maximum range; Min, minimum range; SD, standard deviation.
All of the values depicted in the table are in millimeters (mm)
Table 4
Mean, standard error, minimum and maximum values of various parameters of otolith
dimensions
|
Parameters
|
Mean ± SE
|
Min
|
Max
|
|
Otolith length (OL)
|
0.74 ± 0.1
|
0.54
|
1.07
|
|
Otolith width (OW)
|
0.91 ± 0.0.2
|
0.61
|
0.98
|
|
Relative antirostrum height (A)
|
28.8 ± 1.68
|
14.03
|
65.74
|
|
Relative antirostrum length (AL)
|
8.51 ± 0.60
|
17.89
|
2.75
|
|
Relative rostrum height (R)
|
55.4 ± 2.05
|
18.10
|
75.79
|
|
Relative rostrum length (RL)
|
14.3 ± 1.25
|
4.53
|
33.27
|
Abbreviations: Max, maximum range; Min, minimum range; SE, standard error.
All the values depicted in table are in millimeters (mm).
Table 5
Descriptive statistics of shape indices of Puntius sophor
e
|
Shape indices
|
Mean
|
SD
|
SE
|
Min
|
Max
|
|
Form factor
|
31.91
|
5.20
|
0.81
|
0.31
|
34.57
|
|
Aspect ratio
|
0.82
|
0.1
|
0.02
|
0.61
|
0.98
|
|
Rectangularity
|
34.03
|
2.57
|
0.40
|
28.52
|
39.86
|
|
Circularity
|
1.36
|
3.93
|
0.61
|
2.35
|
27.72
|
Abbreviations: Max, maximum range; Min, minimum range; SD, standard deviation; SE,
standard error.
Fig. 2 Puntius sophore otolith (a) dorsal view of the left sagitta otolith, (b) ventral view of left sagitta
otolith showing the cauda, the rostrum, the antirostrum, and the angle of excisura.
Fig. 3 Relationship between (a) otolith length and fish total length, (b) otolith width
and fish total length, (C) head length and otolith length, and (d) head length and
fish total length.
Discussion
Otolith morphology has proven to be a powerful and vital tool in various taxonomic
studies. Among the three otoliths, the sagitta otolith has been extensively utilized
in various taxonomic studies related to age, growth, feeding habits, and stock identification,
due to its larger size and great interspecific variability.[10]
[13]
[14]
[25] The present study has aimed to examine the relationship of fish TL and HL with otolith
dimensions (OL and OW) by a linear regression model. The otolith dimensions (OL and
OW) and fish body relationships have been studied in various marine fish species by
linear regression models.[15]
[26]
[27]
[28]
[29]
[30]
[31]
[32] The results of the present study depicted that the OL and the OW were linearly correlated
to the TL of the fish. The HL of the fish also showed positive correlation with the
OL. The OW was found to be a better parameter than the OL in estimating fish length.
Hence, it is suggested that otolith dimensions increase as fish length increase and,
therefore, otolith growth can be correlated with fish growth. These results are similar
to previous studies.[33]
[34]. However, other studies depicted that the relationship of otolith variables and
fish somatic growth are not necessarily linear.[35]
[36] In studies on the relationship between otolith and fish size, the OL was usually
used.[15]
[26]
[37]
[38]
[39] The present study supplies supplementary information by considering both the OL
and the OW, as well as the HL of the fish. The present study also described various
other morphometric parameters to give a detailed observation of the shape of the otolith.
When comparing the values of the OL and of the OW of both right and left otoliths,
no statistically significant difference was observed, which was consistent with the
previous findings of different authors.[29]
[32]
[35]
[40] But some studies of sciaenid fishes, such as Micropogonias furnieri and Macrodon ancylodon, and of teleost fishes, such as Lycodes palearis (Zoarcidae) revealed inverse findings.[15]
[41] Concerning the findings of the present study, it becomes evident that the knowledge
of the otolith morphometrics is considered an important marker in the identification
of species and in many other ecological studies that aimed to determine the prey size
based on otoliths obtained from the stomach contents of piscivorous predators, because,
when the relationship between the OL and the TL in a species is determined, the TL
or standard length of a fish can be easily estimated from its OL, or vice versa.[28]
[31]
[33] The present study also provides a better understanding in the identification of
the stock.
