Sexual dimorphism and reproductive biology of bronze featherback ( Notopterus notopterus, Pallas 1769) from Kelekar River, Ogan Ilir, South Sumatra, Indonesia

Sexual dimorphism and reproductive biology are fundamental aspects of fish breeding studies. The aim of this research was to analyze the sexual dimorphism and reproductive biology of Notopterus notopterus . A total of 74 N. notopterus were collected from the Kelekar River in Ogan Ilir Regency, Indonesia, consisting of 38 males (TL: 18–23.6 cm; BW: 35.1–92.1 g) and 36 females (TL: 19.6-26.3 cm; BW: 49.4–133.8 g). Seventeen morphometric characters, three meristic characters, and five reproductive biological parameters were analyzed. The results showed the differences in the morphometric characteristics of male and female N. notopterus . However, there was no difference in the meristic characters. The male gonadosomatic index ranged from 0.15 to 0.61%, and the female from 1.12 to 9.10%. The hepatosomatic index of males ranged from 0.19 to 1.38%, and that of females ranged from 0.15 to 1.23%, with a sex ratio of 1.056:1, fecundity of 1.007–3.901 eggs, ova diameters of 1.1–3.9 mm, and maturity levels of developed gonads to mature for males and mature to spawning for females. In conclusion, the differences between male and female N. notopterus can be identified morphologically.

Fishery management mainly depends on knowledge of fish reproductive biology 27,28 .In adult fish, sexual dimorphism is a frequent and well-known phenomenon 29 .The majority of fishes are gonochoristic and have various sexually dimorphic characteristics in their secondary sexual characteristics 30 .Distinguishing characteristics for the morphological qualities of many teleosts have been documented, including body color, ornamental patterns, breeding tubercles on the snout, pectoral fins and scales, fin hooks, body shape, fin size and shape [31][32][33][34][35] .
N. notopterus is one of the most valuable freshwater fish in South Sumatra, Indonesia.This fish is utilized by the community in South Sumatra, especially as a daily side dish and a raw material for the culinary industries of pempek (fish cake) and kerupuk-kemplang (fish crackers

Materials and Methods
The fish collection was conducted in Kelekar   In the laboratory, fish were weighed using a digital scale (accuracy 0.01 g).Then observe the fish morphologically and count the meristic characters (number of rays of the dorsal fin, number of rays of the pectoral fin, and number of rays of the anal fin).Furthermore, the samples were measured for morphometric characters using a caliper (accuracy 0.01 cm) and a ruler (accuracy 0.1 cm).The morphometric characters measured were seventeen characters (Fig 2).Next, the fish were dissected, and the gonads and liver were taken, separated from other organs.Gonads and liver were weighed for the calculation of gonadosomatic index (GSI) = [gonad weight (g) / fish weight (g) x 100] and hepatosomatic index (HSI) = [liver weight (g) / fish weight (g) x 100] 36 .The calculation of fecundity was done gravimetrically, namely, the fish gonads were taken partially, and then the number of eggs in the partial gonads was calculated.Fecundity = [number of sample gonad eggs x (total gonad weight/partial gonad weight)] 37 .Oocyte diameter was observed under a digital microscope.The maturity level of fish gonads was categorized based on the morphology and color of the gonads, GSI, and oocyte diameter.The sex ratio was calculated based on the number of male and female fish.The data obtained were grouped into two categories, namely male and female fish.Data tabulation using the Microsoft Excel program was then analyzed descriptively to obtain differences between male and female fish.The dorsal fin of N. notopterus fused with the caudal fin and anal fin.Each fin contains only rays and no spine.Meristic characters have been successfully counted.The results showed that P.10-14, D.6-9, and A+C.107-118.The results of the study by 38 showed that P.11-14, D.5-7, and A.98-111.According to 39 , the number of rays on the P.13-14, D.7-9, and A.97-111.However, 40 stated that D.7-9, and A.97-111.According to 8 , P.13-14, and A. 99-111.

Results and Discussion
One of the vital physiological processes that is essential to the life cycle of any organism, including fish, is reproduction 41 .Planning improved conservation and management strategies for fishery resources requires a fundamental understanding of the reproductive cycle of fish 28,42 .Some aspects of N. notopterus reproductive biology observed in this study are presented in Table 2.The GSI utilized to ascertain the fish's reproductive periodicity 43 .Table 2 shows that the GSI value of female fish was highest in February, and the male fish was highest in March.The GSI of female fish is higher than that of male fish.The GSI value is also related to the stage of gonad maturity.The GSI value increases with increasing gonad maturity.The increase in GSI indicates a developmental process in the gonads.The GSI value will reach a maximum value before spawning occurs.In addition, the GSI value is influenced by environmental factors related to the food availability as an energy source for somatic development and fish reproduction 44 .
HSI values for female fish were highest in April and for males in May.HSI is the percentage value of the ratio between liver weight and total body weight.One of the organs that plays a role in fish reproduction is the liver.The liver plays an important role in the vitellogenesis process.This process is triggered by the increasing concentration of estradiol in the blood.Estradiol is an important hormone produced by the ovaries in female fish that is beneficial in the process of vitellogenesis.The higher the level of estradiol concentration in the blood, the earlier the liver will carry out the vitellogenesis process, and gonad maturation will be faster 45,46 .The HSI indicated an energy reserve in the liver 47 and a bio-indicator of contaminant exposure 48,49 .The fecundity of N. notopterus in this study ranged from 1.007 to 3.901 eggs per individual. 50showed that fecundity values ranged from 53 to 748 and from 175 to 4.494 51 .The value of fecundity is influenced by several factors, one of which is environmental.Variations in the number of fish fecundities are also caused by variations in the length and weight of fish.
The diameter of the ova of N. notopterus in this study ranged from 1.1 mm to 3.9 mm.Previous studies ranged from 1.05 to 2.2 mm 9 .The oocyte diameter is categorized as a mature ovary.The higher the oocyte diameter value, the higher the ovary's maturity.The results showed that the diameter of the oocyte in the ovary varied.This indicates that the development of oocytes in the ovary is not uniform.It is suspected that N. notopterus spawns gradually.This is by the opinion of 9 that N. notopterus releases mature oocytes gradually.N. notopterus spawns more than once during a spawning season.The sex ratio is an important component in the study of fish reproduction 42,52 .The balance of the number of male and female fish in a body of water affects the continued existence of a species.The results of this study show that the number of male fish is higher than the number of female fish, except in the May sampling period.This result indicates that the population of male fish is greater than that of female fish.

Conclusion
There are differences in the morphometric characteristics of male and female N. notopterus.However, there are no differences in meristic characters.The gonadosomatic index of male fish ranged from 0.15% to 0.61%, and that of females ranged from 1.12% to 9.10%.The hepatosomatic index of male fish ranged from 0.19% to 1.38%, and females ranged from 0.15 to 1.23%; the sex ratio of the sample fish obtained was 1.06:1.The fecundity value of the sampled fish ranged from 1.007 to 3.901.The oocyte diameter of the sample fish ranged from 1.1 to 3.9 mm.The gonadal maturity stage of the sample fish was at the developing to mature stage for males and mature to spawning for females.