Length and weight Assessment
The weight and length data of the examined specimens are presented in Tables 1 and 2. The investigated R. kanagurta exhibited total weight and length varying from 117.4 to 331 g (mean = 162.7 ± 26) and 20.3 to 32.7 cm (mean = 25.19 ± 2.54), respectively, in the years 2017–2018. Similarly, the weight and length of the observed R. kanagurta in the years 2018–2019 ranged between 130 and 284 g (mean = 269 ± 2.45) and 20.8 and 34.4 cm (mean = 36.6 ± 1.25), respectively. The findings embodied in the current study are in compliance with the results of Siddique et al. (2022), who reported that the length of P. niger ranged from 24.2 to 43.5cm (male) and 24.4 to 43.9 cm (female), while the weight ranged from 410.3 to 1280.3g (male) and 320.3 to 1282.9g (female), respectively.
Table 1
Descriptive statistics and estimated parameters of LWRs of R. kanagurta during 2017-18
Sex
|
n
|
Length range
|
Weight
Range
|
a
|
b
|
r2
|
(cm)
|
(g)
|
Male
|
184
|
20.3–31.5
|
117.4–235
|
0.002
|
3.14
|
0.89
|
Female
|
116
|
20.7–32.7
|
125.2–331
|
0.003
|
3.20
|
0.92
|
Combined sexes
|
300
|
20.3–31.5
|
117.4–235
|
0.004
|
3.07
|
0.88
|
Table 2
Descriptive statistics and estimated parameters of LWRs during 2018-19
Sex
|
n
|
Length range
|
Weight range
|
a
|
b
|
r2
|
(cm)
|
(g)
|
Male
|
162
|
20.8–31.6
|
130-277.5
|
0.002
|
3.20
|
0.94
|
Female
|
138
|
21-34.4
|
128–284
|
0.004
|
3.26
|
0.94
|
Combined sexes
|
300
|
20.8–31.6
|
130-277.5
|
0.003
|
3.10
|
0.93
|
Length weight relationship (LWR)
Tables 1 and 2 display the weight and length measurement, the weight and length relationship (a and b), and the coefficient of determination (r2) of the collected fish species. The LWRs of R. kanagurta during the 2017–2018 research period showed positive allometric growth. The allometric coefficients (b) for the examined fish species varied from 3.07 to 3.14. The highest (b) values were observed in female species, while the lowest (b) values were observed in the combined sexes of R. kanagurta. Likewise, in the first year of the study (2017–2018), R. kanagurta also illustrated a positive allometric pattern of growth in the second year of the study (2018–2019). The allometric coefficients (b) for the examined fish species varied from 3.10 to 3.26. The highest b values were observed in female species, whereas the lowest values were recorded in combined sexes. In both years of the study, significant variations were exhibited among the sexes of fish. A fish exhibiting positive allometric growth extends larger in weight as compared to length (Nguyen et al. 2023). Usually, fat fish show positive allometirc growth. The weight of the fish also increases during breeding seasons owing to enlarged ovaries. Consequently, LWRs are a sign of gonad development (Tran et al. 2021). A correlation was carried out to determine the relationship between the total weight and ovary weight of the corresponding fish (Table 7). The results showed that a linear positive correlation (r = 0.57) was exhibited between total weight and ovary weight. Moreover, the relation between fish total length and body weight of R. kanagurta was also positive, except in male species during 2017–2018 (Fig. 1). It is evident from the result that both studied parameters were correlated.
The regression analysis for all sampled male, female, and combined sexes was calculated separately, which indicated a high positive relationship between length and weight (Tables 1 and 2). The value of r2 calculated (2017–2018) ranged from 0.88 to 0.89, while in 2018–2019, the value was recorded in the range of 0.93 to 0.94. In both years of study, the weight and length of female species have shown a high association as compared to male species, indicating that fish total weight is strongly related to their length. The high coefficient values r2 obtained in the current study in the assessment of LWRs during the study period suggested a high prediction of the corresponding fish in this geographical area. Similar findings were reported by Jisr et al. (2018), who opined that a high coefficient (r) shows linear regression, predicting that the fish species under study are of good quality and that the results can be extrapolated for future catches. The calculated LWRs of R. kanagurta indicated positive allometric growth in males and females in both years of research. The LWR is crucial for measuring species growth, stock assessment, body transformation, gonadal growth, and feeding rate of fish (Alam et al. 2013). Generally, fish with thin, elongated bodies have values of b less than 3, while thicker ones have values greater than 3. This determines somatic growth (isometric or allometric). Values smaller, equal, and larger than 3 indicate isometry, negative allometry, and positive allometry, respectively (Kuriakose 2017). The present values of the growth parameters were found to be in the range of those recorded for the same species in other localities (Rahman and Hafzath 2012; Sivadas et al. 2006; Jayabalan et al. 2016). For instance, in agreement with our results, Nguyen et al. (2023) reported a positive allometric growth in Bostrychus sinensis inhibiting Indo-Pacific goby in Vietnam. Keyombe et al. (2015) reported positive allometric growth for Clarias gariepinus in Lake Kenya. Similarly, Epinephelus marginatus caught from the Atlantic displayed positive allometric growth (b = 3.094) (Condini et al., 2014). Furthermore, the findings in the current study are contradictory to Ahmed et al. (2022), who reported negative allometric growth in R. kanagurta collected from coastal areas of Balochistan. Variations in LWR among different species and even the same species collected from different parts of the world may be caused by the state of the species, its phenotypic characteristics, its particular geographic location, and consequently its environment (Jisr et al. 2018; Fetouh and El-Far 2023).
Condition Factors
Condition factors (Fulton’s condition factor (kc) and Relative condition factor (kn)) are widely used for assessing the health of fish species. It indicates physical and biological changes due to interactions with feeding conditions and physiological factors, indicating the general fish condition (Nguyen et al., 2023). It is important for effective culture system management as it provides producers with specific information about the specific conditions under which organisms are developing (Hammock et al. 2022). Kc in 2017–18 was observed from 1 to 1.33 (Table 3). The lowest value of kc was found in the male population (0.95), whereas the highest kc values (1.33) were observed in the female population. The kc in R. kanagurta fluctuates from 1 to 1.34 during 2018–19. The highest kc value was recorded in females (1.34), while the lowest was observed in combined sexes (0.95). Significant (p < 0.05) variations in kc were observed between the male and female, while temporal variations in kc were not statistically significant (p > 0.05). kc is used for evaluating fish health in both years of study; it was equal to and above 1, indicating fish in good health condition. The mean kn values in both years of the study were equal to 1 in all studied specimens (Table 4). The study found that female fish exhibited significantly (p < 0.05) higher kn values compared to male fish; however, there were no significant (p > 0.05) variations in the value of kn over time. The kn is a quantitative measure showing the degree of fatness and development stage of the fish and also reflecting the present and future population growth patterns. Moreover, studying condition factors is crucial for comprehending fish species' life cycle, including spawning season, and aiding in effective management (Karupiah et al. 2022). The findings of the current study revealed that the kn values for R. kanagurta were greater than one, indicating that the fish had good health, which could be due to prevailing favourable environmental factors resulting in higher productivity. The results of the study are in agreement with the findings of Santos et al. (2022), who reported that condition factor values were greater than one in fish caught from the Brazilian coast, indicating favourable environmental conditions and nutrient availability.
Table 3
Fulton’s condition factor (kc) of R. kanagurta during the study period
Sex
|
2017–2018
|
2018–2019
|
Condition
|
P value
|
Male
|
1 ± 0.092
|
1 ± 1.92
|
Suitable
|
0.0001
|
Female
|
1.33 ± 2.42
|
1.34 ± 1.22
|
Suitable
|
Combined sexes
|
1 ± 0.34
|
1 ± 0.45
|
Suitable
|
P = 0.08
|
Range
|
1-1.33
|
1-1.35
|
Suitable
|
Table 4
Relative condition factor (kn) of R. kanagurta during the study period.
Sex
|
2017–2018
|
2018–2019
|
Condition
|
p value
|
M
|
1.03 ± 1.23
|
1 ± 0.34
|
Suitable
|
0.0000
|
F
|
1.04 ± 0.48
|
1.26 ± 0.29
|
Suitable
|
C
|
1.01 ± 3.49
|
1 ± 0.9
|
Suitable
|
p = 0.1
|
Range
|
1-1.63
|
1-1.26
|
|
Note: Male (M), Female (F) and combined sexes (C) Kn ≥ 1.0 suitable |
Fecundity
Fish fecundity, influenced by aquatic environment diversity, is crucial for species survival and population size, resulting in variations in egg amounts across individual species and populations. (Malick et al. 2023). Table 5 displays data regarding the fecundity of the female fish. In the current study, the mean fecundity was 51450.4 eggs (2017–2018) and 46671.1 eggs (2018–2019), the relative fecundity was 352.91 eggs/g (2017–2018) and 277.8 eggs/g (2018–2019), the ovary weight was 9.11 g (2017–2018) and 8.1 g (2018–2019), the mean total length was 25.3 cm (2017–2018) to 25 cm (2018–2019), and the fish weight was 150.3 g (2017–2018) and 162.1 g (2018–2019). The highest fecundity was seen in July, while the lowest fecundity was observed in February 2017–2018, whereas in the 2nd year of study (2018–2019), the highest rate of fecundity was observed in June and the lowest fecundity was recorded in February (Fig. 2). The fecundity rate began to rise from March to October and then decreased from November to January. The findings of the study were contrasted with research conducted in a different region of the world (Table 6). Several investigations have assessed the fecundity potential of R. kanagurta in other parts of the world. The comparison illustrated that the fecundity reported in the current study was lower than reported in Indonesia. Oman and India. It has also been noted that the fecundity increased with an increase in the length of fish in both years of study (Fig. 3). The study examined the correlation between mean fecundity and body length, weight, ovary weight, and water quality parameters from 2017–2019 (Table 7). Fecundity is positively correlated with body length (r = 0.82), body weight (r = 0.89), and ovary weight (r = 0.59), as well as its correlation with water quality parameters, i.e., temperature (r = -0.52), DO (r = 0.82), EC (r = -0.78), TDS (r = -0.51), and salinity (r = -0.51). Fecundity in fish is influenced by factors like fish size, weight, age, and life-history traits, as well as environmental conditions like food supply, population density, and temperature. Numerous authors have reported similar observations, such as Bakht et al., 2020, Burbank et al., 2022 and Fasya et al., 2022. Hansen et al. (2012) analysed the impact of water temperature on fecundity in Atlantic cod brood stock. Results showed that the May and July spawning groups produced more eggs per kg of fish and had higher egg fertilization success. Siddique et al. (2022) reported an increase in the mean fecundity of P. niger in July and also determined a positive correlation between fecundity and body weight, length, and ovary weight. Temporal variations in the studied parameters were statistically non-significant (p < 0.05).
Table 5
Reproductive characteristics of female R. kanagurta during the study period.
Variables
|
2017–2018
|
2018–2019
|
P value
|
Mean fecundity
|
51450.4 ± 3.89
|
46671.1 ± 3.69
|
0.38
|
Relative fecundity
|
352.91 ± 2.90
|
277.8 ± 2.21
|
0.28
|
Ovary weight (g)
|
9.11 ± 5.90
|
8.1 ± 4.3
|
0.05
|
Total length (cm)
|
25.3 ± 2.59
|
25 ± 2
|
0.07
|
Fish weight (g)
|
150.3 ± 3.91
|
162.1 ± 4.1
|
0.05
|
Table 6
Comparison of the fecundity of R. kanagurta in the current study with other countries.
Study Area
|
Mean fecundity
|
Reference
|
Present study ( Gawadar, Pakistan)
|
51450.4- 46671.1
|
……………..
|
Java Island, Indonesia
|
70,945.5
|
Nurfaiqah et al., 2023
|
India
|
1,08,266
|
Bhendarkar et al., 2018
|
Indonesia
|
14,800
|
Olii et al., 2023
|
Oman
|
98,273
|
Zaki et al., 2016
|
Western Waters of Aceh, Indonesia
|
56,635
|
Arrafi et al., 2016
|
Maharashtra, India
|
91,258
|
Hulkoti et al., 2013
|
Table 7
Pearson correlation coefficient ( r) of mean fecundity with body length and weight ,ovary weight and with the water quality parameters.
Variables
|
Mean fecundity
|
Body Length
|
Body weight
|
Ovary Weight
|
Relative fecundity
|
pH
|
Temperatue
|
|
DO
|
EC
|
TDS
|
Salinity
|
Mean fecundity
|
1
|
|
|
|
|
|
|
|
|
|
|
|
Body Length (cm)
|
0.82
|
1
|
|
|
|
|
|
|
|
|
|
|
Fish Body weight
|
0.89
|
-0.47
|
1
|
|
|
|
|
|
|
|
|
|
Ovary Weight
|
0.59
|
0.84
|
0.56
|
1
|
|
|
|
|
|
|
|
|
Relative fecundity
|
-0.18
|
0.81
|
-0.43
|
0.94
|
1
|
|
|
|
|
|
|
|
pH
|
0.21
|
-0.19
|
0.09
|
-0.02
|
0.12
|
1
|
|
|
|
|
|
|
Temperature
|
-0.52
|
0.44
|
0.16
|
0.32
|
0.55
|
0.28
|
1
|
|
|
|
|
|
DO
|
0.82
|
-0.42
|
0.92
|
-0.37
|
-0.31
|
-0.09
|
0.27
|
|
1
|
|
|
|
EC
|
-0.78
|
0.32
|
0.55
|
0.27
|
0.37
|
0.02
|
0.77
|
|
0.61
|
1
|
|
|
TDS
|
-0.51
|
0.44
|
0.09
|
0.35
|
0.57
|
0.25
|
0.80
|
|
0.13
|
0.68
|
1
|
|
Salinity
|
-0.51
|
0.45
|
0.22
|
0.44
|
0.58
|
0.01
|
0.85
|
|
0.40
|
0.85
|
0.64
|
1
|
Gonadosomatic Index (GSI)
The GSI is a measure of fish's gonadal development and maturity, indicating their spawning season, which increases with maturity and then drops abruptly (ElGazzar et al. 2022). In the current study, GSI was measured month-wise to assess the spawning season of R. kanagurta (Fig. 4). The results embodied in this study revealed that it spawns throughout the year. According to the 2017–2018 results, the GSI value peaked in March and April, decreased in May and June, then surged once again in July and August, and finally showed a declining tendency from September to December. The 2018–2019 statistics show that the GSI values peaked in April to June, fell in July, then surged once again in August to October, and finally decreased in November and December. The GSI values ranged from 2–31 to 12.87 (2017–2018) and from 1.03 to 9.47 (2018–2019), respectively. The correlation coefficient (R2) indicated a positive relationship between GSI and body weight and length in both years of the study (Fig. 5). These findings illustrate that the spawning seasons of R. kanagurta showed temporal variations at the study sites. Overall, the data suggest that R. kanagurta has two spawning seasons: the first occurs from March to April (2017–2018) and April to June (2018–2019), and the second takes place from June to August (2017–2018) and from August to October (2018–2019).
Researchers reported seasonal variations in GSI values for different areas, with peaks in spawning occurring in a few months in a year (Shim et al. 2017; Jayabalan et al. 2021; Mascarenhas et al. 2023). In R. kanagurta, mature gonads were observed throughout the year, with some species spawning in April, May, June, September, and October (Pour et al. 2014; Piah et al. 2016; Kantun et al. 2018). R. kanagurta was found to have varying gonadal maturity levels, tend to spawn as partial spawners, and breed multiple times throughout the year (Piah et al. 2016). The findings of the study are in agreement with the study of Soe et al. (2022), who examined the reproductive biology of R. brachysoma, a short mackerel species off Pattani Bay, revealing two GSI peaks during different spawning seasons. Variations in GSI in the two years of the study were statistically non-significant (p < 0.05).
Physicochemical analysis of Water
The physico-chemical parameters such as pH, EC (µs/cm), temperature (˚C), DO (ppm), TDS (ppm), and salinity (ppm) were assessed monthly during the study period. The results are presented as the annual mean during the study period, along with desirable limits for the growth of fish (Table 8). The pH was 7.8 ± 0.38 (2017–2018) and 8.16 ± 0.74 (2018–2019), Temperature was 25 ± 3.82 (2017–2018) and 24.9 ± 4.56 (2018–2019), DO was 9.4 ± 1.99 (2017–2018) and 10 ± 3.12 (2018–2019), EC was 14 ± 0.87 (2017–2018) and 14.68 ± 0.89 (2018–2019), TDS was 133 ± 3.67 (2017–2018) and 130.79 ± 3.9 (2018–2019), and salinity was 35.8 ± 1.7 (2017–2018) and 34.9 ± 2.1 (2018–2019), respectively. Generally, the assessed water quality parameters except DO lie in the range recommended for the optimal growth of fish (Stone and Thomforde 2004). A correlation matrix analysis was carried out to assess the association between the analysed water quality parameters (Table. 7). The study reveals an association between water quality variables, with significant positive correlations indicating a close connection between these parameters. For instance, a positive correlation was shown between temperature and EC, TDS, and salinity, whereas DO has exhibited a positive correlation with EC, and EC has shown a positive correlation between TDS and salinity. Similarly, a positive correlation was also found between TDS and EC. Temporal variations among the studied parameters were statistically significant (p < 0.05) except temperature and DO.
Table 8
Assessment of water quality parameters during the study period.
Variables
|
2017–2018
|
2018–2019
|
Desirable limits
|
P value
|
pH
|
7.8 ± 0.38
|
8.16 ± 0.74
|
6.5 to 9
|
0.03
|
Temperature (°C)
|
25 ± 3.82
|
24.9 ± 4.56
|
25–32°C
|
0.46
|
D O (ppm)
|
9.4 ± 1.99
|
10 ± 3.12
|
4–5 ppm
|
0.17
|
EC (µS/cm)
|
140 ± 0.87
|
140.68 ± 0.89
|
30 − 5,000 µS/cm
|
0.001
|
TDS (ppm)
|
133 ± 3.67
|
130.79 ± 3.9
|
400 ppm
|
0.002
|
Salinity (ppm)
|
35.8 ± 1.7
|
34.9 ± 2.1
|
34–36 ppm
|
0.03
|