First reference on reproductive biology of Butis koilomatodon in Mekong Delta, Vietnam

Ovarian and spawning reference, size at first maturity and fecundity of Glossogobius giuris caught along Vietnamese Mekong Delta

Populations of Periophthalmus chrysospilos, the Gold‐spotted mudskipper, within the Mekong Delta are facing extirpation risks due to indiscriminate harvesting for the growing aquarium and food‐fish trade. This study provides some of the first information on reproductive ecology—such as spawning type and season, length at first maturity, and batch fecundity—of this species, to be used in their management. The sex ratio of wild populations, based on 1031 individuals (523 males and 508 females) is 1:1. The gonadosomatic index (GSI) values are exhibit a non‐normal distribution and changed with gender, season, and site. A combination of GSIs and the monthly appearance of mature gonads suggest that this species reproduces throughout the year, with peak from July to October. This species exhibits sexual and spatial variation in size at first maturity (Lm ) as Lm is 6.2–8.6 cm in males and 6.4–7.3 cm in females. The batch fecundity (F = 2614 to 23,465 eggs/female) exhibits non‐normal distribution and varies with site, with the highest values at Dam Doi, Ca Mau (13,336 ± 1,279 SE) and the lowest at Tran De, Soc Trang (6654 ± 851 SE). In addition, batch fecundity is directly proportional to body size due to high determination relationships between batch fecundity and fish size (r 2 > 0.64 for all cases). Information derived on the reproductive biology of this species can inform its conservation, sustainable exploitation, and ex situ propagation.

This study contributed to the variation of morphometric and meristic measurements of Glossogobius sparsipapillus , a target catching fish in the Mekong Delta. A total of 583 individuals (293 males and 290 females) were collected during dry and wet seasons (April 2019 to January 2020) at three studied sites from Vinh Hau, Hoa Binh, Bac Lieu to Dien Hai, Dong Hai, Bac Lieu and Tan Thuan, Dam Doi, Ca Mau. The analysis results showed that total length and body weight of this species varied with seasons and studied sites, but not genders. The variations of fish length and weight of males and females depended on seasons but not studied sites. The interaction of site and season variables influenced the change of fish length and weight. The results supplied additional knowledge for fish identification and ecological adaptation understanding in the study regions.

Caragobius urolepis has a wide range of distribution, from brackish to freshwater water, ranging from India to the Philippines and Fiji, including the Vietnamese Mekong Delta (VMD), where it lives mainly in the coastal regions and plays a vital role in food supply. Our preliminary observation showed that its population tended to decline, but little is known about this species. This study, therefore, was conducted to provide data on the ovarian structure, spawning pattern and season, length at first maturity, and batch fecundity of this fish. The study of 306 specimens caught with trawl nets from April 2022 to March 2023 in two coastal areas of VMD—Dong Hai, Bac Lieu (DHBL), and Dam Doi, Ca Mau (DDCM)—showed that this goby spawned more than once because the oocytes in stage IV ovary showed different stages of development. It could release eggs monthly during a 12-month study, with a peak in July–September since stage IV ovaries were found monthly during the study period and the GSI exhibited a high value in July–September. The fish length at first maturity and batch fecundity varied with the site, as they were 18.8 cm and 3,757–9,187 (6,142 ± 707 SE eggs/female) in DDCM and 20.5 cm and 3,760–11,118 (5,634 ± 750 SE eggs/female) in DHBL. The findings provide valuable foundations for exploiting their resources and serve as a basis for studying artificial reproduction. It is suggested to avoid catching these fish species during the breeding season to ensure sustainable exploitation in the future.

This study provides new data on the characteristics of the gastrointestinal morphology and the variation of Clark index according to sexes, fish size groups, seasons and sampling sites of mud sleeper Butis koilomatodon, one of the commercially valuable gobiid species in the Mekong Delta. Analytical results of 1,227 fish samples collected monthly from April 2019 to March 2020 in Duyen Hai (Tra Vinh), Cu Lao Dung (Soc Trang), Tran De (Soc Trang), Hoa Binh (Bac Lieu), Dong Hai (Bac Lieu) and Dam Doi (Ca Mau) showed that this species had a slightly sloping mouth, the length between two jaws was relatively equal, teeth were small and grew in long lines on both jaws with the outer row having larger teeth. The length of the gut was shorter than the total length of the fish and so this species belonged to predator group. The Clark index depended on length of fish, sampling time and site but excluding season and gender. It was also effected by interactions of fish length x season; fish length x site and season x site. Conversly, the interactions of gender x season and gender x site did not impact on the Clark index. The outcomes of research will provide useful data in artificial aquaculture Butis koilomatodon.

Reproductive biology of brownstripe snapper Lutjanus vitta (Quoy and Gaimard, 1824) from West Sulu Sea, Philippines

Gulamah fish is a bycatch that is commonly found in the waters of the City of Tarakan. Gulamah fish in Tarakan City is processed into salted fish which produces offal waste and swimming bubbles. Swimming bubbles are known to have high collagen content. The purpose of this study was to obtain information about the length relationship between fish weight and swim bladder as well as the collagen characteristics of the gulamah swim bladder. The research was conducted in 2 stages, namely the length-weight analysis stage with swimming bubbles, and the second stage, namely the extraction and characterization of collagen from the swimming bladder of gulamah fish. The relationship between fish length and weight is a positive allometric, while the relationship between fish length and fish weight and swimming bladder of fish is a negative allometry. The physical chemical parameters of collagen obtained water content values of 29.28% - 29.30%, protein 2.86% - 2.88%, fat 9.53% - 9.55% and viscosity 11.5 ?sp.Gulamah fish is a bycatch that is commonly found in the waters of the City of Tarakan. Gulamah fish in Tarakan City is processed into salted fish which produces offal waste and swimming bubbles. Swimming bubbles are known to have high collagen content. The purpose of this study was to obtain information about the length relationship between fish weight and swim bladder as well as the collagen characteristics of the gulamah swim bladder. The research was conducted in 2 stages, namely the length-weight analysis stage with swimming bubbles, and the second stage, namely the extraction and characterization of collagen from the swimming bladder of gulamah fish. The relationship between fish length and weight is a positive allometric, while the relationship between fish length and fish weight and swimming bladder of fish is a negative allometry. The physical chemical parameters of collagen obtained water content values of 29.28% - 29.30%, protein 2.86% - 2.88%, fat 9.53% - 9.55% and viscosity 11.5 ?sp.

Spatial and interannual variability in Baltic sprat batch fecundity

Summary This work focuses on reproductive biology aspects of Uranoscopus scaber from the coast of the Aegean Sea. In total, 175 U. scaber specimens were collected in Izmir Bay using trawl nets from January to December 2005. The reproduction period according to gonadosomatic index (GSI) values extents from March to September, with a peak in May (6.32 ± 1.2). Oocyte diameters taken from 59 mature gonads ranged from 62 to 1860 μm. Maximum batch fecundity (BF) was 58091 (mean: 11556 ± 1445) in large oocytes in May, and 8408 (mean: 2821 ± 945) in hydrated oocytes in September. The BF increased with total length and body weight, excluding the ovaries. Total length (TL)–BF relationships and fish weight–BF relationships were BF = 0.0034TL4.6248 (r = 0.47) and BF = 59.166W−3101 (r = 0.49), respectively, according to the oocyte size frequency method. There was a linear relationship between BF and fish size.

This study provided new knowledge on reproductive traits of the unique mudskipper Periophthalmodon septemradiatus that is also a potential aquarium pet. Fish specimens were obtained by using fishing rods at the muddy flat in tributaries of the Hau River from August 2017 to July 2018. Data analysis of a collection of 1,504 individuals (930 males and 674 females) showed that the sex ratio of this species was significantly different from the ratio 1:1. As mature gonads were found monthly during the study period, it is suggested that P. septemradiatus is an iteroparous species releasing eggs for a year‐round cycle. The fish length at first mature (Lm) showed an increase from estuary to upstream areas. Male P. septemradiatus had higher Lm values than that of females. Likely, the batch fecundity increased from estuary region (5,916 ± 312 SEM eggs) towards upstream area (11,451 ± 953 SEM eggs). The fish total length and weight values had strong positive relationships with batch fecundity, as shown by high determination values (r2), suggesting that batch fecundity increased with fish size. This study provided more information on reproductive biology of P. septemradiatus, which can be utilized for fish population conservation and artificial reproductive study.

Temporal variation in length-weight relationship, growth and condition factor of Acentrogobius viridipunctatus in the Mekong Delta, Viet Nam

Flood dynmics in the Vietnamese Mekong Delta : Current state and future projections

The reproductive biology of the European hake ( Merluccius merluccius , Linnaeus, 1758) was studied on the eastern central Atlantic Moroccan coast from November 2001 to December 2003. The sex ratio was close to 1:1 for the specimens with a total length of less than 45 cm. European hake spawned all year round, though two spawning peaks were recorded with a certain interannual variability: the first and main peak in winter and a secondary intermittent peak in summer. Length at first maturity was estimated as 28.6 cm and 33.8 cm total length for males and females, respectively. These values are closer to Mediterranean than Atlantic hake values. The mean batch fecundity was 299872 eggs ind –1 . The relative batch fecundity was estimated as 228 eggs per gram of gutted weight. Batch fecundity increased proportionally with fish length and weight. The batch fecundity of European hake in the Moroccan Atlantic area is higher than that in northern Atlantic and northwestern Mediterranean areas.

Tongue Fish (C. lingua) is a fish that has a flat body like a tongue, has a non-bilateral symmetrical body, a blunt head, and belongs to the family Cynoglossidae. Tongue fish (C. lingua) usually lives on the bottom of muddy waters or mud mixed with sand and in river estuaries. The purpose of this study was to obtain related information about the analysis of the length and weight of the Tongue Fish (C. lingua) in the Berombang River, Panai Hilir District, Labuhanbatu Regency. This research lasted for 3 months, starting from October-December 2021. The sampling location was based on information from local fishermen. Fish samples were taken using nets, starting at 08.00 WIB - 16.00 WIB. The analysis carried out is the biological aspect of the relationship between length and weight of fish using a linear allometric model (LAM), while the ecological aspect that is measured is the condition factor using the K Fulton equation and the relative weight equation (Wr). In this study, 60 samples of Tongue Fish (C. lingua) were caught, with different lengths and weights. Where the total length ranges from 195-370 mm, with the total length of the dominant tongue fish on average 250 mm. While the weight of the Tongue Fish (C. lingua) ranged from 30-213 grams, and had an average dominant weight of 87 grams. The results of the long-weight relationship explained that the growth of the Tongue Fish (C. lingua) was positive allometric with the b value obtained, namely b > = 3, which was 3.3226.

Phylogenics of the genus Glossogobius in the Mekong Delta based on the mitochondrial cytochrome b (cytb) gene