835-840Sagor catfish (Hexanematichthys sagor Hamilton, 1822) is one of the most popular fish caught in Can Gio reserve biosphere. A study on reproductive biology was conducted to evaluate the reproductive parameters, including male–female distinction, gonadal development stages, sex ratio, spawning season, fecundity, and size at first sexual maturity. The results showed that the number of males and females in the nature was not significantly different. Male and female fish can be distinguished when they reach the mature size. Gonadal of the fish pass through five stages of maturation. The histological screening of gonad, percentage of maturation stage and gonadal somatic index value of the fish showed all year round spawning with a peak of spawning female from March to August. The length at first sexual maturity of the fish is 25.39 cm. Fecundity ranged from 60 to 145 ovaries/individuals strongly related to weight and length. The current findings provide the scientific foundation for the purpose of fishery resource management and artificial breeding of the blue sagor catfish

Hai, Truong Ba

Lam, Ho Son

Sang, Huynh Minh

English

NOPR

Indian Journal of Geo Marine Sciences Vol. 48 (06), June 2019, pp. 835-840       Reproductive biology of sagor catfish (Hexanematichthys sagor Hamilton, 1822) in Can Gio water, Vietnam Huynh Minh Sang1,*, Ho Son Lam1, & Truong Ba Hai2 1Institute of Oceanography, Vietnam Academy of Science and Technology (VAST) 2Southern Branch, Vietnam Russia Tropical Center *[E-mail: hmsang2000@yahoo.com] Received 14 November 2017; revised 23 April 2018 Sagor catfish (Hexanematichthys sagor Hamilton, 1822) is one of the most popular fish caught in Can Gio reserve biosphere. A study on reproductive biology was conducted to evaluate the reproductive parameters, including male–female distinction, gonadal development stages, sex ratio, spawning season, fecundity, and size at first sexual maturity. The results showed that the number of males and females in the nature was not significantly different. Male and female fish can be distinguished when they reach the mature size. Gonadal of the fish pass through five stages of maturation. The histological screening of gonad, percentage of maturation stage and gonadal somatic index value of the fish showed all year round spawning with a peak of spawning female from March to August. The length at first sexual maturity of the fish is 25.39 cm. Fecundity ranged from 60 to 145 ovaries/individuals strongly related to weight and length. The current findings provide the scientific foundation for the purpose of fishery resource management and artificial breeding of the blue sagor catfish. [Keywords: Sagor catfish; Hexanematichthys sagor; Reproductive biology; Can Gio] Introduction In Vietnam, the marine natural resource, especially, the resource of high value species has been rapidly decreasing1. One of the main reasons for the decrease of the resource is overexploitation. In addition, there is no reasonable management strategy for sustainable and environment-friendly exploitation of the natural resource. The research on biology of a marine species including reproduction and growth is necessary for management of natural resource. The reproductive cycle of fish is closely tied to the environmental changes, particularly temperature, photoperiod and food supply2. Reproductive parameters, such as gonadal development stages, sex ratio, sex at first maturity, spawning season, and fecundity are of great value in fishery resource management and aquaculture practices. The availability of quality seeds and the ability to control fish reproduction are widely recognized as limiting factors in the farming of any commercial species3. Sagor catfish (Hexanematichthys sagor Hamilton, 1822) belongs to the genus Hexanematichthys, family Ariidae, the main economically valued group4. In Vietnam, the genus Arius distributes mostly in the South5. Sagor catfish is a high value species. Like other species, the fish is also not sustainably managed in Vietnam and in Can Gio seawater. Thus, there is a great need for a suitable management strategy of the natural resource of the fish as well as the strategy for effective breeding of this fish for supporting the demand. However, information available on the reproductive biology of this fish in Can Gio seawaters is still unknown. Hence, a detailed investigation on reproductive biology of this fish, including male-female distinction, sex ratio, gonadal development stages, spawning season, and fecundity and size at first sexual maturity in Can Gio seawater was conducted and the results discussed in this paper.  Materials and Methods  Sample collection The study was carried out from September 2016  to August 2017. Fish sample was collected from  Can Gio. Around 30 ramdom-size fish were  collected each month (Table 1). The fishes were transported to laboratory at the Institute of Oceanography, Vietnam, for analysis. At the laboratory, the fish were killed, weighed and their lenght measured. Reproductive gonad of the fish (testes or ovaries) were then dissected and weighed for further analysis. INDIAN J. MAR. SCI., VOL. 48, NO. 06, JUNE 2019   836Sample analysis and data collection The distinction between male and female was determined based on the appearance of anus and genital papilla, followed by determination of sex ratio. Chi-square test was used to test the difference in the number of males and females in the natural population of the fish.  The maturity stages of females were recognized based on the macroscopic appearance of the ovary in the body cavity and microscopic structure of ova; in males, only the macroscopic appearance of testes were considered. Gonadal development stages of fish were determined by methods of Nikolsky5 and Xakun & Buskaia6 using Olympus BX50 microscope at 10X magnification. Histological analysis of testes and ovary was performed following the method described by Gen et al7. Ovaries or testes of each gonadal development stage of fish were dissected and fixed in 4% buffer formalin for 24h. After dehydrating by passing the tissue through a series of alcohol solutions of 70, 85 and 98%, the samples were vacuum-embedded in paraffin. The histological sections (4-5 µm) were stained for general morphological purposes with haematoxylin and eosin. The samples were photographically analyzed and documented using the Olympus BX 50 microscope at 10X and 40X magnification.  Spawning season of the species was determined based on the availability of mature and spent individuals in the commercial landings during different months and the monthly gonado-somatic indices (GSI). The GSI was calculated using the formula: GSI = 100 * (GW/BW), where GW is weight of gonad and BW is weight of fish. To estimate the length at first maturity (Lm), the females were grouped separately into 8 mm class intervals and fish in stage-III and above were considered mature. Length at first sexual maturity (Lm) were defined as the length at which 50 per cent of all female fish having ovaries at advanced stage of development7. The proportion of the female fish with ovaries at advanced stage of development (P) of each size group was adjusted by correction factor, as the biggest size group was 100%. The linear relationship between size group and Ln(1-P/P) was determined and the Lm was calculated at P = 0.59.  Table 2 — Distinction between mature male and female of  sagor catfish Male Female Have the genital papilla Do not have genital papilla Belly is slim and rather hard Belly is larger than male, soft Genital hole is small and light in color. Genital hole larger, pink in color.  Mouth cavity is larger  Mouth cavity is small  To estimate fecundity, 30 ovaries in stage–IV were utilised. From formalin-preserved ovary of known weight, a small portion was removed and weighed to the nearest 0.001 g in an electronic balance and then kept in modified Gilson’s fluid for two days. All the oocytes in the sample ovary were counted under binocular microscope using a counting chamber. The absolute fecundity was estimated using the formula: Absolute fecundity (F) = (weight of ovary/weight of sample) x number of oocytes in the sample. The relationship between fecundity and total length and weight was determined using the formula: LogF = aLogX + b where F is demoted fecundity, X is total length or weight, a and b are constant. Relative fecundity was calculated using the formula: S=F/W where S is relative fecundity and W is fish weight (g).  Results Male–female distinction of the sagor catfish: In the sagor catfish that has not matured, it is not possible to distinguish between male and female based on the external characteristics. However, when the fish are mature, male and female can be distinguished by way of several signs (Table 2):  Sex ratio of the sagor catfish Ratio of male and female was 1:1.07. Number  of male and female was not significantly different  (χ2 = 0,41< 3,845 (df = 1, P < 0,05)).  Gonadal maturity stages of the sagor catfish in Can Gio The maturity stages of ovary and testes of the sagor catfish in Can Gio is represented in Tables 3 and 4. The histology of ovaries and testes of the blue tang fish in Can Gio is presented as Figures 1 and 2. Monthly change in the percentage of maturity stage of the sagor catfish in Can Gio The fishes at mature, stage-III to spent, stage-V  of  ovaries  are  presented  all  year  round.   However,  Table 1 — Number of fish collected each month during the study period Month Jan Feb Mar Apr May Ju Jul Aug Sep Oct Nov Dec No 30 30 30 29 31 30 30 32 28 30 30 31  SANG et al.: REPRODUCTIVE BIOLOGY OF SANGOR CATFISH   837  Fig. 1 — Ovary and histological section of the ovaries of the sagor catfish in Can Gio(a, b: stage-I; c,d: stage-II; e, f: stage-III; g, h: stage-IV)   Fig. 2 — Testes and histological sections of the testes of the sagor catfish in Can Gio(a, b: stage-I; c,d: stage-II; e, f: stage-III; g, h: stage-IV; ) Table 3 — Maturity stages of the female sagor catfish in Can Gio Maturity stages Particular of the gonads Stage-I, Immature Ovary was thin, short and glassy in appearance. It could not be distinguished ovary and testes by snake-eyes. The ovary contain only ovogony at the size about 0,08 ± 0,04 mm. The stages was observed in the fish sizeunder the first maturation size.  Stage-II, Maturing Ovary developing, ovary and testes can be distinguished by snake-eyes. The egg increase the size to2.8 ± 1.2 mm diameter.  Stage-III, Mature Ovary increase the size comparing to stage II. Egg diameter range from 4.4 to 5.8 mm. Histological sectionshow the round nuclear at the center of the egg. Stage-IV, Ripe/Oozing End of the maturation process, the ovary filling the entire body cavity, extending in the entire body cavity length. The egg diameter range from 6.7 to 12.3 mm.  Stage-V, Spent Ovaries are rather flaccid.  Table 4—Maturity stages of the male sagor catfish in Can Gio Maturity stages Particular of the gonads Stage-I, Immature Testes was thin, short and glassy in appearance. It could not be distinguished ovary and testes by snake-eyes. The stages was observed in the fish size under the first maturation size.  Stage-II, Maturing Testes start developing, ovary and testes can be distinguished by snake-eyes. Testes are moderately thick,flattened and white.  Stage-III, Mature Testes increase the size comparing to stage II. Testes are flat, well-developed and creamy white, extendingabout 2/3 body cavity length Stage-IV, Ripe/Oozing Testes are very thick, flat, turgid and creamy, extending in the entire body cavity length Stage-V, Spent Testes are sunken  INDIAN J. MAR. SCI., VOL. 48, NO. 06, JUNE 2019   838percentage of fish at maturation stages-III, IV and V was higher during the period from March to August than that during the period from September to February. The percentage of advance stage of ovaries (III, IV and V) in July was the highest (82%) and the lowest was in January 41 (%) (Fig. 3).  Monthly change in GSI of the sagor catfish in Can Gio GSI of the females was the highest in July (5.15 ± 2.85) and the lowest in November (0.85 ± 0.42). For males, the highest GSI was in July (1.12 ± 0.95) and the lowest GSI was observed in December (0.30 ± 0.25) (Fig. 4).  Length at first sexual maturity of the sagor catfish in Can Gio The length of the first sexual maturity of the sagor catfish in Can Gio was counted at 25.38 cm (Fig. 5).   Fecundity of the sagor catfish in Can Gio The absolute fecundity of the sagor catfish in  Can Gio was 120.50±25.48 ovaries/individual (ranged from 60 to 145 ovaries/individual). The relative fecundity of the fish was 0.165±0.043 ova/g of  female fish (ranged from 0.125 to 0.225 ova/g of female fish). The relationship between fecundity and the length and weight of the fish is presented in Figures 6 and 7.   Fig. 3 — Monthly percentages of maturation stages of the sagorcatfish in Can Gio    Fig. 4 — Monthly change of the GSI of the sagor catfish in Can Gio   Fig. 5 — Groups of size relationship and Ln ((1-P) / P) of the sagor catfish in Can Gio    Fig. 6 — Fecundity - total length relationship of the the sagor catfish in Can Gio    Fig. 7 — Fecundity - total weight relationship of the the sagor catfish in Can Gio SANG et al.: REPRODUCTIVE BIOLOGY OF SANGOR CATFISH   839Discussion Reproductive characteristic of fish is necessary for fishery resource management and aquaculture practices. The current study is the first attempt to investigate some reproductive parameters of the sagor catfish in Can Gio, one of the important reserve biospheres in Vietnam. Results show that the gonad of the sagor catfish was divided into five stages of maturity. This is normally observed in the tropical fish having the year-round reproduction cycles. At mature or ripe stages, beside the main component oocytes (oocyte at early vitellogenic and advanced vitellogenic stages), the primary growth oocytesalso exist in considerate number. This is the signal that the sagor catfish spawns continuously during the spawning season. In addition, the data on the changes in percentage of maturity stages and GSI in the current study suggests that the sagor catfish spawns all year round with a peak season from March to August. The results are consistent with other studies on tropical marine fish, such as Galeichthys felis, and Arius sciurus 9. The fishes in estuary and coastal seawater almost spawn year round and have one peak spawning season11; 12. The data on changes in GSI and the monthly change in the percentage of maturity stage of the sagor catfish in Can Gio also shows that the fishes have peak spawn in the month of July. The results are consistent with other studies on the fishes belonging to family Ariidae, such as Arius thalassinus from February to July13; Arius felis from May to August; Galeichthys felis from April to July14; and Barge marinus from April to June15. The fecundity of fishes is usually determined  from the number of ova of the mature group in  the ovary. In the present study, the fecundity of the sagor catfish was determined from the examination of 30 specimens. The fecundity showed high correlation coefficient with the total length of the fish. The regression of fecundity and total length can be expressed as LogF = 0.578 *Log(TL ) + 0.393 with R2 value as 0.930. The regression of fecundity  and body weight can be expressed as LogF = 1.8*Log(BW) - 0.913 with R2 value as 0.888. The absolute fecundity of the sagor catfish in Can Gio is higher than that of other fishes belonging to the family Ariidae: Arius felis (20–64 ova/fish)16, Galeichths felis (40–62 ova/fish)14, and Tachysurus thalassinus (25-42 ova/fish17. In contrast, the fecundity of sagor catfish is lower than that of Arius sciurus (Absolute fecundity range from 461–1,047 ova/fish and relatively fecundity range from 11.813–16.362 egg/kg)9. The fecundity of sagor catfish is similar to that of Arius thalassinus having absolute fecundity from 85–153 ova/fish and relatively fecundity from 11.5–21.5 egg/kg)13.  The current study also showed that the sagor catfish longer than 44 cm has the mature percentage of 100%, the fish shorter than 20 cm is not mature, and the fish longer than 26 cm has mature percentage of more than 50%. The calculated result show that the length at first sexual maturity of the sagor catfish in Can Gio is 25.39 cm with a very strong correlation between the length and percentage of maturation  (R = 0.9662). The length at first sexual maturity  of the sagor fish in Can Gio is similar to Arius felis (23.6 cm), larger than Arius melanopus (16.3 cm) and Galeichths felis (19 cm), but smaller than Tachysurus thalassinus (36 cm)17.   Conclusion The present study reveals that the sagor catfish in Can Gio seawater spawns year round with peak season from March to August; The length at first sexual maturity of the fish is 25.39 cm. The fecundity ranged from 60 to 145 ovaries/individual and is strongly related to weight and length. The currently findings provide the scientific foundation for the purpose of fishery resource management and artificial breeding of the sagor catfish.  Acknowledgement Authors would like to thank the Aquaculture Department – Institute of Oceanography for all the supports and facilities  References 1 Ronald, D. Z., Ha Xuan Thong, Le Thanh Luu, Jonathan R. C.k, Michael P. Viet Nam: Fisheries Sector Research. (2005), pp. 135. 2 Baganal, T. B., Aspects of fish fecundity. In: Ecology of freshwater fish production (Welly, Newyork) (1978), 75-101. 3 Shamsan, E. F. and Ansari Z. A., Studies on the reproductive biology of Indian Sand Whiting Sillago sihama (Forsskal). Indian J. of Mar. Sci., 39 (2010). 280-284. 4 Romero, P., An etymological dictionary of taxonomy. Madrid, unpublished (2002). 5 Nguyen, V. H., Freshwater fish in Vietnam, Three in a class of fish bone, Vol III, Agricultural Publishing press, Ha Noi, (2005), pp759. 6 Nikolsky, G. V., The ecology of fishes. Academic press, London, (1963). 7 Sakun, O. F. and Buckaâ, N. A.., Opredelenie stadii zrelosti i izuèenie polovyh ciklov ryb. 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Reproductive biology of sagor catfish (Hexanematichthys sagor Hamilton, 1822) in Can Gio water, Vietnam

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Reproductive biology of sagor catfish (Hexanematichthys sagor Hamilton, 1822) in Can Gio water, Vietnam

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