Length–weight relationships and condition factors of mullets Liza macrolepis and Moolgarda engeli (Pisces: Mugilidae) harvested from Lambada Lhok waters in Aceh Besar, Indonesia

Introduction

Mullets (Mugilidae) represent a family of euryhaline fish that can tolerate a wide range of salinity^1,2. This fish is frequently found in marine environments, brackish and fresh water^2–7. To date, a total of 30 genus belonging to 78 species of mullets have been described worldwide^8,9. A total of 21 species of mullets have been reported in Indonesian waters, and among them, four species have been recorded in the waters of Aceh province; these are Liza melinoptera, Mugil chepalus, Valamugil cunnesius, and V. speigleri^4,10,11. Our previous study recorded three additional mullets from Aceh waters, namely, L. macrolepis, Crenimugil crenilapis, and Moolgarda engeli (Yulianto, thesis in preparation), which accounted for a total of seven species of mullets in the Aceh region. These additional species are commonly found in Lambada Lhok, Aceh Besar district close to Banda Aceh City, the capital of Aceh province, Indonesia. Moreover, our field observation showed that L. macrolepis and M. engeli were the predominant species among other mullets in this area.

The coastal area of Lambada Lhok has a mangrove forest; however, the forest area has been significantly decreased due to tsunami disaster in 2004, land conversion for settlement and aquaculture ponds. The other potential threats are pollution from domestic waste, fishing port, and tourism activities^12,13. Mullets are a species of shoaling and schooling fish commonly found in river mouths for feeding^14,15, which then subsequently migrate to deep waters for spawning¹⁶. Therefore, these fish are highly susceptible to exposure to pollution from coastal areas; for instance, Chelon subviridis from Donan River estuary, Central Java, have been contaminated by cadmium and copper¹⁷. A similar finding has been reported in M. cephalus from the Ligurian Sea in Italy¹⁸. In addition, L. macrolepis and M. engeli have been harvested intensively by local fishermen, thereby increasing the pressure on these fish. Thus, research related to bioecology as basic information is crucial in planning an effective conservation strategy. The two important pieces of information are length–weight relationships (LWRs) and growth pattern and condition factors.

The study of the LWRs and condition factors has become popular and is therefore commonly conducted by fish biologists¹⁹. The objectives of LWRs study are to determine the specific weight and length variations of fish individually or the population a whole to determine the age, obesity status, health, productivity, and physiological conditions, including gonadal development^20,21. LWRs analysis is also useful to estimate the fish condition or plumpness index, which is an important variable in the evaluation of the health conditions of fish populations or individuals^22–24. The condition factor indicates the biological and physical conditions of fish and its fluctuations by interaction among feeding condition, food reserves, and parasite infestation^25–27.

Several studies on LWRs and condition factor of mullets have been conducted, such as, that on M. dussumieri in Ujung Pangkah, East Jawa, Indonesia¹⁴; on LWRs in L. macrolepis from Indian waters^28,29, and on L. macrolepis from Taiwanese waters³⁰. In addition, the study of LWRs in several species of mullets in Aceh waters, Indonesia has been reported by Mulfizar et al.³¹ in M. chepalus from the waters of Kuala Gigieng, Aceh Besar, and by Muttaqin et al.³² in the same species from Madat waters in East Aceh. However, no study has been published on L. macrolepis and M. engeli. Thus, the objectives of the present study are to analyze LWRs and condition factor of these two types of mullet harvested from Lambada Lhok waters.

Methods

Time, site, and sampling

The sampling was conducted from July to November 2018 in the Lambada Lhok estuary, Aceh Besar regency in Aceh province, Indonesia (Figure 1). The location is a small river mouth and deforested mangrove areas and fishing port (5°36'57.6" N, 95° 23'25.6" E). The sampling was done purposively at these locations as they were easy to access and fish were reported to be present. Sampling was conducted four times a month for five months. The target species in this study were determined based on preliminary survey and observations on the composition of local fishermen catches, where Liza macrolepis and Moolgarda engeli were the dominant species caught.

Figure 1. Map of Lambada Lhok coastal area showing the sampling location (5 ° 36'57.6 "N, 95 ° 23 '25.6" E).

The fish was caught using gillnets with a mesh size of 2.0 inch. The gillnets were set up in the waters for 4 h (06.00 AM –03.00 PM) and were monitored in 30 min intervals. The sampled fish was washed, euthanized with cold water 4 °C for 5 min. This euthanize method was chosen as it is easy to apply, non-toxic and inexpensive. Then the fish was preserved temporarily in crushed ice in a styrofoam box, and then transported to a laboratory for further analysis. Other species of fish caught were separated from the mullets, and released back to the waters if still live, but the fish taken for consumption if they died during sampling. All efforts were made to ameliorate harm to the animals by complying to the guidelines of ethics animal use in research of Syiah Kuala University.

Field observations

During this process, the weather condition, tides, and water turbidity are also observed visually during the sampling.

Results

Length-weight relationships

The field observation of the catch composition showed that Liza macrolepis and Moolgarda engeli were predominant. A total of 242 L. macrolepis and 109 M. engeli were sampled and measured in the study. The length of male L. macrolepis ranged from 141.4 – 202.1 mm (164.8 ± 15.03 mm), and ranged from 129.2–185.4 mm (159.1 ± 12.66 mm) for females. The body weight of male L. macrolepis ranged from 34.7 g to 89.6 g (54.1 ± 13.3 g in average), and 28.8 g to 75.13 g (47.9 ± 9.52 g in average) in females. The length of the male M. engeli ranged from 109.9–188.5 mm (161.9±20.83 mm) and 116.5–182.3 mm (154.1 ± 18.94 mm) for females. The body weight of the males was 13.6 – 108.5 gram (47.6±19.3 gram), and that of the females was 14.2–75.1 gram (41.4 ± 16.43 gram). Raw data are available as underlying data³⁷.

The results of the LWRs analysis on L. macrolepis showed that the male fish had a b value of 2.49 with a correlation coefficient of 0.93, and the female fish had a b value of 1.81 and a correlation coefficient of 0.82 (Figure 2a and 2b). Therefore, the male and female L. macrolepis displayed negative growth patterns, and a moderate correlation between body weight and total length of the fish. The results of LWRs analysis of male M. engeli revealed that the average b value was 3.22 with a coefficient correlation of 0.89. The female M. engeli had an average b value of 3.41 with a coefficient correlation of 0.93 (Figure 3a and 3b). These data indicate that the male and female M. engeli have a positive allometric growth pattern, and a strong correlation between body weight and total length.

Figure 2.

The length-weight relationship of Liza macrolepis based on linear allometric model (a) male, (b) female; Comparison of observed and predicted growth for male (c), and female (d) of Liza macrolepis. R2 - determination coefficient, r - correlation coefficient, N - number of fish sampled.

Figure 3.

The length-weight relationship of Moolgarda engeli based on linear allometric model (a) male, (b) female; Comparison of observed and predicted growth for male (c), and female (d) of Moolgarda engeli. R2 - determination coefficient, r - correlation coefficient, N - number of fish sampled.

Based on sampling season, the average b value of L. macrolepis (male and female) was 2.78 during the dry season and 2.28 during the rainy season (Figure 4a). The b value of M. engeli was 3.42 during the dry season and 2.48 during the rainy season (Figure 4b). These data indicate that the b value is lower during the rainy season for both species. The scatter plots of predicted standard weight for respective observed length, as calculated from the composite of length–weight regression, are presented in Figure 2c and 2d and Figure 3c and d. The regression models show a difference between the observed and predicted growth patterns in both species.

Figure 4.

The length-weight relationship of Liza macrolepis (a) during dry season (b) during rainy season and Moolgarda engeli (c) during dry season (d) during rainy season. R2 - determination coefficient, r - correlation coefficient, N - number of fish sampled.

Condition factors. The results showed that the male L. macrolepis had a Fulton’s condition (K) factor of 1.19, and relative weight condition factor (Wr) of 100.11; while the females had a Fulton’s condition factor of 1.19, and relative weight condition factor of 100.01. In addition, male M. engeli had a Fulton’s condition factor of 1.05, and relative weight condition factor of 101.08; whereas the females has Fulton’s condition factor of 1.06, and relative weight condition factor of 100.61 (Table 1). Based on sampling season, the Fulton’s condition of L. macrolepis during the dry season was 1.22 and 100.49 for the relative weight; during the rainy season these were 1.19 and 101.74, respectively. In addition, the K and Wr values of M. engeli during the dry season were 1.03 and 102.09, respectively; during the rainy season these were 1.09 and 100.47, respectively (Table 2).

Table 1. The b value, coefficient of correlation and determination, and condition factors of Liza macrolepis dan Moolgarda engeli sampled from July-November 2018 according to sex.

Species	Sex	Body weight (mean ±SD) (gram)	Total length (mean ± SD) (mm)	N	b value	Coefficient of correlation (r)	Coefficient of determination (R2)	Fulton condition factor (K)	Relative weight condition factor
									(Wr)
L. macrolepis	Male	34.7 – 89.6 (54.1 ± 13.3)	141.4 - 202.1 (164.8 ± 15.03)	172	2.49	0.93	0.85	1.19 ± 0.12	100.11 ± 09.38
	Female	28.8 – 75.1 (47.9 ± 9.52)	129.2 – 185.4 (159.1 ± 12.66)	70	1.81	0.82	0.65	1.19 ± 0.19	100.01 ± 11.23
M. engeli	Male	13.6 – 108.5 (47.6 ± 19.3)	109.9 – 188.5 (161.9 ± 20.83)	68	3,22	0.89	0.90	1.05 ± 0.15	101.08 ± 14.74
	Female	14.2 – 75.1 (41.4 ± 16.43)	116.5 – 182.3 (154.1 ± 18.94)	41	3.41	0.93	0.94	1.06 ± 0.25	100.61 ± 11.72

Table 2. The b value, coefficient of correlation and determination, and condition factors of Liza macrolepis dan Moolgarda engeli sampled from July-November 2018 according to sampling seasons.

Species	Season	Body weight (mean ±SD) (gram)	Total length (mean ± SD) (mm)	N	b value	Coefficient of correlation (r)	Coefficient of determination (R2)	Fulton condition factor (K)	Relative weight condition factor
									(Wr)
L. macrolepis	Dry	30.4 – 80.2 (49.6 ± 11.17)	138.4 - 193.7 (158.9 ± 11.37)	92	2.78	0.90	0.82	1.22 ± 0.11	100.49 ± 59.56
	Rainy	34.7 – 85.5 (53.9 ± 13.35)	129.2 – 202.1 (159.1 ± 12.66)	150	2.28	0.89	0.79	1.19 ± 0.15	100.58 ± 10.89
M. engeli	Dry	13.6 – 108.5 (32.1± 18.42)	109.9 – 182.9 (142.4 ± 17.51)	59	3.42	0.79	0.82	1.03 ± 0.29	102.09 ± 24.18
	Rainy	41.2 – 74.5 (56.2 ± 9.31)	153.1 – 188.5 (172.1 ± 8.97)	50	2.48	0.78	0.63	1.09 ± 0.11	100.47 ± 09.81

Discussion

The study revealed that male and female L. macrolepis had negative allometric growth patterns. However, the b value of the females was less than that of the male. The b value of the male M. engeli showed a positive allometric growth pattern. Based on these growth pattern data, the study indicated that M. engeli grows better than L. macrolepis, thereby indicating that M. engeli is more adaptable to the environmental condition of Lambada Lhok waters. Furthermore, the field observation on the catch composition of the fishermen showed that M. engeli was also predominant. The Fulton’s condition factor showed a slight difference in K value between the male and female for both species, where the K value was higher than 1. According to Morton and Routledge³⁶, a fish population is in good condition when the K value is higher than 1. The study showed that the K value of L. macrolepis ranged from 1.16 to 1.22, and 1.03 to 1.09 for M. engeli; therefore, both populations are in good condition, in dry and rainy season, respectively. In addition, the relative weight condition factor of both species is close to 100, indicating a balance between prey and predator²⁰. These results show that these waters provide a sufficient food source for these species. The relative weight condition factor also corresponds to fish health conditions, stock estimates, and management levels^{23,35,36,38,39}. Therefore, the Lambada Lhok waters provide sufficient food sources for mullets.

The results also showed differences in growth patterns during the dry and rainy seasons, and that the fish grew better during the dry season. The probable reason is that the waters are clear and a maximum rate of sunlight penetrates into the waters, triggering the growth of phytoplankton and algae. Algae is a primary food item for the mullets^40–43. By contrast, turbidity and currents were higher during the rainy season⁴⁴, and thereby presume to inhibit the growth of phytoplankton and algae as important food item for mullets. A similar phenomenon was reported by Chu et al.³⁰, who found a negative growth pattern in L. macrolepis in Taiwan during winter, and an isometric growth pattern during summer and spring. Moreover, Sandhya and Shameem²⁹ observed a negative growth pattern in L. macrolepis in polluted waters, in contrast to an isometric growth pattern in unpolluted waters. According Muchlisin et al.²², besides being affected by the environmental factors, the growth pattern of fish is also influenced by fish behavior; for example, the fish that were active swimmer had a lower b value than those that were passive swimmers^45–47.

The average correlation coefficients of L. macrolepis were 0.93 and 0.89 in females and males, respectively, whereas M. engeli had a correlation coefficient of 0.89 for males and 0.93 for females. In general, the correlation coefficients of L. macrolepis and M. engeli tend to be similar (above 75%), indicating a strong correlation between total length and body weight. The determination coefficients of L. macrolepis were 0.85 and 0.65 for the male and female fish, respectively, which means that approximately 65%–85% of total variants can be explained by the model, while M. engeli had a value of 0.90 and 0.94 for males and females, respectively, indicating that 90%–94% of variants can be explained by the model.

Conclusion

The results of this study showed that L. macrolepis had a negative growth pattern, whereas M. engeli had a positive allometric growth pattern. These growth patterns were better during the dry season for both species. Condition factors showed that the environmental condition of Lambada Lhok remains suitable for the growth of the mullets, and the density of prey and predator is balanced.

Data availability