Length-Weight Relationships of Four Fish Species from Qinzhou Harbor, Guangxi, China

This study determined the total length-weight relationships of the four fish species, Inegocia japonica, Gerres decacanthus, Sillago asiatica, and Evynnis cardinalis, belonging to four families. Fishes were collected using commercial trawls from Qinzhou harbor, China. Samples were collected quarterly from March to December 2017. Total length and weight of each specimen were recorded with an accuracy of 0.1cm and 0.1g, respectively. During the sampling period, a total of 111 fish individuals were collected and measured. The allometric coefficient (b) of length-weight relationship varied from 3.08 for Evynnis cardinalis, 3.17 for Inegocia japonica, 3.18 for Sillago asiatica and 3.19 for Gerres decacanthus. Growth was found as isometric for this four fish species.


Introduction
The length-weight relationship (LWR) is often used to evaluate the standing stock biomass and is also used to analyze the ontogenetic changes and is also used in the assessment of fish in population dynamic [1]. There are very high number and endemic species of fishes in Chinese Sea [2]. However, biological characteristics of some fish species have seldom been researched. The length-weight relationship (LWRs) is an important tool for management and conservation of fisheries [3][4]. This study provides the first LWRs reports for these four fish species from Qinzhou harbor of China.

Materials and Methods
Fish samples were collected quarterly from March to December 2017 using commercial trawls from Qinzhou harbor of China. After captured, all specimens were stored on ice and transferred to laboratory. The species were identified according to studies by Lai (2016) [5], Liu (2016) [6] and He (2013) [7]. For each specimen, the total length was recorded with an accuracy of 0.1 cm, and body weight was measured with 0.1g accuracy in Laboratory. The total length was measured with a Vernier caliper from the end of snout to the base of tail. For each species, the length-weight relationships were determined by the function, W = aLb, where W is the weight (g) and L is the total length (cm), was fitted with a simple linear regression model using log-transformed data. The 95% confidence interval (CI) was determined for parameters "a" and "b" [8]. "a" is the intercept of the regression curve and "b" is the regression coefficients. The best appropriate model was selected based on R2 value [9]. The observed differences were evaluated statistically using SPSS 13.0 and Statistical Analysis System [10].

Results and Discussion
During the sampling period, a total of 111 fish individuals belonging to four species was collected and measured. Mean total length and weight in four fish species from the Qinzhou harbor is summarized in Table 1. In this study, the total length varied from 88.0 cm to 196.0 cm and weight between 3.5g to 55.5g, mean total length as 153.5 cm and weight as 28.7g for Inegocia japonica. The total length ranged from 53.0 cm to 124.0 cm and weight from 1.6g to 28.6g, mean total length as 91.8 cm and as 12.1g in weight for Gerres decacanthus. The total length oscillated from 78.0 cm to 178.0 cm, weight from 3.7g to 36.0g, mean total length as 128.5 cm and weight as 17.1g for Sillago asiatica. For Evynnis cardinalis, the total length ranged from 73.0 cm to 124.0 cm and weight from 7.5g to 41.6g, mean total length as 109.2 cm and weight as 28.7g.  Figure 1 shows the relationship between total length and weight of four different fish species sampled during the study, and the regression parameters "a" and "b", and the correlation coefficient (R2) are shown in Table 2.
The allometric coefficient "b" of LWRs varied from 3.08 for Evynnis cardinalis, 3.17 for Inegocia japonica, 3.18 for Sillago asiatica and 3.19 for Gerres decacanthus. The values of parameter "b" remained within the expected range of 2.5-3.5 (Froese, 2006). Comparing our results with the Bayesian LWRs predictions in Fishbase, the "b" values of these four fish species fell within the 95% confidence intervals of the prediction and were thus not significantly different. Length-weight relationships may change among individuals in different species can be affected by many factors, such as small juvenile specimen, the sample size, size-weight distribution, sampling time, sex, gonad maturity, habitat, season, stomach fullness, diet, the length ranges used, and ecological conditions [11][12].

Conclusions
In terms of fisheries biology and management, it is critical for sustainable ecosystem management of continuous monitoring in nature. Therefore, it is believed that these studies should be carried out to monitor fish resource in the region. In addition, the results of this study will be an important database for future studies of fish species. In general, the study provides basic information on the LWRs of these four fish species, which could useful for sustainable management of fishery in Qinzhou harbor of China.