Length-weight Relationship and Fecundity of Parastromateus niger from Gwadar Port Balochistan Province, Pakistan

Gwadar, a very important port city of Balochistan province located on the southwestern sea coast of Pakistan with a population of roughly 50,000, is found at the top of Arabian Sea and at the mouth of the Persian Gulf (FAO, 2002). Fish has importance from economic point of view (Pathak et al., 2019), as for several economically developing nations, fish is the first or second largest export product (FAO, 2002). Being a healthy choice over several animal proteins, sea feed is on an increasing demand around the world (FAO, 2002; Gowsalya et al., 2020), transported among various countries and therefore the freshness or quality of these products are of vital importance, because it reflects dominantly over its value (FAO, 2002).
       
Parastromateus niger, is one of the important fish species from the economic point of view (Salim et al., 2020; Islam et al., 2021), with systematic position of this species as among the perciform (Bloch, 1795). These fishes are exported to various countries of world like China, Sri Lanka, Thailand, Malaysia and Japan, which is an important factor to boost the economic growth of Gwadar. This fish is utilized for eating and medicinal purpose and huge number of Gwadar residents are involved in export of this fish species, thus employing it as a source of income (Fisheries Department, 2010).
       
In order to analyze the changing trend in fish populations and level of fish exploitation, studies on their age, growth and population dynamics are important (Liu, 2008). An essential factor for determining growth and biology of a fish in any sort of environment, is the length-weight relationship (Hubert, 1999; Qadri et al., 2017). Fish growing process is totally related to number of fishes specific to that area. The attributes of water, food provision and competition between fish species are used to find out the growth rate and increase in size. In the presence of all environmental factors and food supply, the fish will continue to grow, however, the growth of fish will reduce with the limitation of various crucial growth requirements (Hubert, 1999).
       
Apart from length-weight relationship, fecundity is also a crucial factor in revealing growth of fish. The term fecundity refers to the fish’s egg laying ability specifically in a spawning season (Lagler, 1956). In order to identify the biology of fish, its production and availability for human food and also for management of fisheries sector, fecundity is of extreme importance. Depending upon the species, fecundity is affected by the presence of food (Nandikeswari and Anandan, 2013; Prasad et al., 2005; Marquez et al., 2003; Tracey et al., 2007). To get idea about the production of eggs, fecundity is practical as it is related to size of female fish (Chondar, 1977). The reproductive capacity or fecundity, indicates increase of fish stocks (Marquez et al., 2003), additionally exact evaluation of fecundity helps to recognize the potential’s recovery of fish population (Lagler, 1956).
       
Research study is largely lacking on the part of this specific fish species (Parastromateus niger) from the coast of Balochistan. Present research study was designed to determine the growth and fecundity of Parastromateus niger from Gwadar Port Balochistan, Pakistan.

Sample collection
 
Parastromateus niger samples were collected every month from August 2017 to July 2019, from the landing station of Gwadar, Balochistan. A total of 600 fish samples were utilized in current research, with a collection of 25 fishes per month from August 2017 to July 2019. Samples were stored in sealed ice boxes and brought to Zoology lab of Sardar Bahadur Khan Women’s University for further study.
 
Growth (Length-weight)
 
Measurements of sample’s length and width were made in centimeters (cm) and body weight was measured in grams (g) respectively. A digital balance (Model No.805A with sensitivity 0.01 gram) was used to calculate samples weight. For measuring fish growth, Length-weight relationship (LWR) is a useful parameter. Data pertaining to length and weight was recorded in length and weight logs, obtained by inspecting male and female samples, accordingly.
 
Analysis
 
Le Cren equation was adopted to calculate length-weight relationship:

W = Total weight in gram (g).
L   = Represents total length of fish in centimeter (cm).
a and b  =  Constants, a shows body form and b show type of growth.
       
For determination of fecundity, only female fish samples were considered (Murua et al., 2003).
 
Dissection
 
The fish was dissected to remove ovary while length and weight were measured before dissection. Weight of ovary was measured by digital weighing machine (Model No.805A with sensitivity 0.01 gram), moreover two lobes of ovary were separated and divided into three equal parts, anterior, posterior and middle. Afterwards, 0.1 g from each portion was taken and soaked in 25% buffer solution (consisting 75 ml distilled water and 25 ml formalin) for 24 hours. Eggs were kept in Petri dish and counted under stereo light microscope (Nikon, YS-100). The sample from the three sub-samples were exploited to find the fecundity by gravimetric method (Yelden and Avsar, 2000).
   
Furthermore, the relative fecundity was calculated by dividing the mean fecundity of the fish to its total weight (g). Similar method was used by Murua et al., 2003, Mustafa et al., 1983, Dewan and Doha, 1979, Shafi et al., 2012 and Doha and Hye, 1970.

Growth
 
Determination of length-weight equation was based independently on sexes. Values of exponent (b) calculated for P. niger was from 2.82 to 2.92 in 2017-18 (Table 1), while the range of (b) value observed in 2018-2019 was from 2.50 to 2.70. The coefficient (b) of female (2.70) was higher than male (2.65) during second year. Value (b<3) shows that fish is lighter in weight and pattern of growth is negative allometry. The regression coefficient R² in 2018-19 was 0.889 in males, 0.912 in females and 0.898 in combine population (Table 1). The highest (b) value was 2.92 obtained in females during first year of research period and lowest value was seen in combine population of P. niger (2.50) in second year of research. The (b) values were less than 3.0 (b<3), showing negative allomertic growth (A-) for both sexes. Length-weight relation of fish gives indication about patterns of fish growth. Fig 1 illustrates the logarithmic relationship between weight and length of males, females and combine population of P. niger with regression values. The regression coefficient between log length and log weight in the year 2017-18 was 0.974 in males, 0.974 in females and 0.975 in combine population (Table 1). Weight and length relationship among combine population of P. niger was represented by R²=0.974 in 2017-18. The value of R² between length and weight in the year 2018-19 was 0.898. Fish weight was directly proportional to its length and hence showing a linear regression equation (Fig 1).
 

 

 
Correlation of fish weight and ovary weight
 
Fish weight and ovary weight relationship expressed as R² was 0.384 in 2017-18. Moreover, ovary weight was not related with total weight of fish, therefore, non-linear relationship was observed. The R² value (0.384) indicates negative correlation. The relation between weight of fish and ovary was R²=0.864 in 2018-19, indicating a strong positive relation.
 
Fecundity
 
The mean ovary weight of P. niger was higher in July 2017-18, which indicates a weight gain in ovary from July onwards. The number of eggs per gram of ovary was comparatively greater in July than in other months, whereas, the number of eggs per kg fish (relative fecundity) was higher in July. Fish weight of P. niger ranged from 410.3 to 954.8 g and ovary weight of fish was between 1.43 g to 25 g, moreover, 43165 was the mean number of eggs in ovary. Mean annual relative fecundity of P. niger was 73 eggs/g and ranged from 5 eggs/g to 172 eggs/g. Highest and lowest values of relative fecundity were obtained in 2017-18 (Table 2).
 

       
In 2018-19, the mean ovary weight of P. niger was maximum in August. The mean annual fecundity in second year of study was recorded as 39759 eggs, which is lower than first year of study. Number of eggs per kg of fish weight was highest in July (158). The fecundity was highest (153175 eggs) in August (Table 2).
 
Fecundity and total length correlation
 
The correlation R² between total length and fecundity was 0.602 and 0.578 in first and second year of study which indicates that the total length and fecundity were positively associated to each other (Fig 2 and 3). Fecundity of P. niger was directly related to fish length.
 

 

 
Correlation of fecundity and fish weight
 
A value of R² 0.596 and 0.809 was calculated for the year 2017-18 and 2018-19 showing a linear relationship among fecundity and fish weight. Fecundity of P. niger was highly related with total weight of the fish. A highly significant linear regression equation was obtained. The R² values 0.596 and 0.809 were significant, indicating a moderate and strong positive correlation (Fig 2 and 3).
 
Correlation of fecundity and ovary weight
 
Correlation among ovary weight and fecundity of fish was determined as R²=0.751 and 0.951 in 1^st and 2^nd year of research, displaying a strong positive correlation (Fig 2 and 3). Fecundity was directly proportional to weight of female fish ovary.
 
Correlation of fecundity and relative fecundity
 
The R² value between fecundity and relative fecundity was 0.545 and 0.968 during 2017-18 and 2018-19 of study showing moderate and strong positive association between relative and mean fecundity of P. niger (Fig 2 and 3).
       
Present findings support the finding of Yadollahvand and Rahnama (2014), who studied P. niger growth and age from Oman Sea. Their research was conducted on 94 fish samples and the value of coefficient (b) was 2.386, which is consistent with our results. Regression analysis between length and weight was R²=0.982. Range of length in Yadollahvand and Rahnama research was 21 cm to 56 cm, which is in accordance with our findings. The value (b) for length and weight calculated in our study was less than 3, which indicates negative allometric growth. Hoque et al., (2018), measured the length weight relation of P. niger with total length of 36.5 to 43 cm, which was quite close to our results and they observed that total weight was between 850 to 1500 g. Fish weight was positively related with fish fecundity, which is similar to current research.
       
Relative fecundity of P. niger in our research work was from 0 to 172 eggs/g. Ovary weight and relative fecundity of fish was high in July. Fecundity relationships with fish length (0.602), total weight (0.596) and weight of ovary (0.751) were linear, indicating normal to strong relation. In many reports, similar association of fecundity with total length, weight and ovary weight was observed. High fecundity in P. niger was reported by earlier researcher from India in 2002, compared to our research (39759.5-43165.4). Simpson (1951), reported the fecundity (84030) of P. niger, from Southern Bight North Sea, which differ from our results, due to various reasons including type of species, size of fish, age of fish and environmental conditions like presence of fish food, salinity and temperature of water. Normal fecundity of P. niger was reported in present work, indicating various reasons that might be responsible for that level of fecundity i.e., genetic makeup of fish or unavailability of feed for fish species that disturb the growth of fish and also cause imbalance development of gonads. Hoque et al., (2018), studied the fecundity of P. niger from Bangladesh, that was between 112170 to 1116228 eggs. Annual mean fecundity was recorded as 512585 eggs. These results do not support our findings, as they observed that there was positive relationship between fecundity and total body weight of fish.

Value of (b) in Parastromateus niger was less than (3), which indicates that fish grows negative allometrically because there are many parameters which are responsible for changing the condition factors of a fish. These parameters include acquiring data, division of obtained data into various groups, type of sex, stages of fish maturity and condition of fish stomach. Values of condition factors also change due to variation in ecological conditions. Observation in this research represents the coefficient of correlation for length-weight relationship being higher, which shows that these two parameters are directly related with each other in studied fish. Fecundity of studied fish in first year of research work was higher in the month of July, while in second year of research, the fecundity was found highest in August. Fecundity of this fish was positively correlated with fish weight, ovary weight, fish length and relative fecundity.

No funding was acquired in this research study.

All the authors declare no conflict of interest in this research study.