USING ULTRASOUND IMAGES AS A TOOL FOR DETERMINING SEX OF STRIPED CATFISH (Pangasianodon hypophthalmus)

Hoa P. Nguyen*, Linh N.T. Bui, Trong T. Tran

Nong Lam University, Ho Chi Minh City, Viet Nam

^*Corresponding author: phuhoa@hcmuaf.edu.vn

Ultrasound images can be utilized as a non-invasive method for sex determination of striped catfish (Pangasianodon hypophthalmus) for future breeding in the reproductive program. Striped catfish of various sizes were examined with portable Mindray Model Z60Vet. The results showed that the best ultrasound images given by Convex probe. Probe frequency 3.5; 5; 7 and 10 MHz are allocated for determining the suitable frequency for this study. The 5 MHz probe was utilized due to viewing area and clearly image which this probe provided. Ultrasound gonad images of matured male and female striped catfish could be distinguished. There was 100 % accuracy on sex determination using ultrasound images when striped catfish were from weight of higher than 1 kg.

Keywords: Ultrasound, probe, frequency, sex determination, striped catfish

GONADAL DIFFERENTIATION AND EXPRESION OF WNT4 IN THE HERMAPHRODITIC ORANGE-SPOTTED GROUPER Epinephelus epinephelus

Long Ba Dam^1*

¹Institute of Aquaculture, Nha Trang University, No 2 Nguyen Dinh Chieu Str., Nha Trang City, Viet Nam

^*Corresponding author: longdb@ntu.edu.vn

Wnt4, a growth factor, have been reported  to have important effects in the process of mammalian gonadal sex differentiation. However, most of studies on roles of this gene in sexual differentiation have only been carried on mammal and very few in fish. The objectives of this study are to investigate expression of Wnt4 in early  gonadal differentiation as well as localization of this gene in gonad of orange-spotted grouper. Gonads at various stages were collected and fixed with 4% paraformaldehyde for 16 hours then dehydrated with methanol for purposes of IHC and ISH staining. The immunohistochemiscal data showed that Wnt4 protein was almost expressed during ovarian development and highly expressed in somatic cells surrounding oogonia (Fig. 1C) and in follicle of early vitellogenic oocytes (Fig. 1C, 1D and 1E). In situ hybridization also showed that Wnt4 transcripts were expressed in the somatic cells surrounding oogonia and primary oocytes (Fig. 1F). The study showed potential roles of Wnt4 in sex differentiation and during development of gonad in orange-spotted grouper.

Fig. 1. Wnt4 expression during ovarian development. Wnt4 immunostaining (brown) in different stages of oocytes includes before sex differentiation (A), starting sex differentiation (B), primary oocyte stage (C), and early vitellogenesis stage (D and E). In situ hybridization of Wnt4 in 1.5-yr-old fish with an antisense probe (F) and with a sense probe (F’’). BV- blood vessel, OG-oogonia, PO-primary oocyte, PVO- pre-vitellogenin oocyte.

Keywords: orange-spotted grouper, sex differentiation, Wnt4, gonad

SEXUAL DIMORPHISM AND REPRODUCTIVE BIOLOGY OF Cephalocassis borneensis  (SILURIFORMES: ARIIDAE)  IN THE MEKONG RIVER

Ngoc Son Le^1,*, Thuy Yen Duong¹

¹College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Viet Nam

^*Corresponding author: lengson02@gmail.com  

Reproductive biology of fish species is important information for fisheries management,  conservation, and culture potential assessment. Thus, this study aimed to understand morphological differences between two sexes and reproductive characteristics of Cephalocassis borneensis, an ariid species with a rapid decline in the Vietnamese Mekong River. Fish samples were collected from local fishermen monthly for a year (n=1092). Their morphological and reproductive parameters were then analyzed, including morphometric indices, length at first maturity (L_m), gonad development, gonadosomatic index (GSI), condition factor (K), fecundity and eggs diameter. The results revealed that sexual dimorphism was observed in mature fish but not in immature ones. Males reached a smaller L_m (11.5cm) compared to that of females (12.5cm). Mature males were characterized by larger head length and pre-pectoral distance compared to mature females. Conversely, females gained three larger head indices (head angle, head width and head deep) and three abdomen indices (body deep, ventral fin length and distance between pectoral and ventral fin). In term of reproductive characteristics, C. borneensis showed a year-round spawning mode, mainly occurring in the rainy season from June to October. At that time, the GSI values were higher in both females and males whereas K values depicted an opposite trend with lower values. The fecundity of this species was relatively low, from 10 to 31 eggs per female with quite large size about 7.30 ± 0.68mm in diameter. Besides, non-functional oocytes or “hyaline eggs” with smaller size (<3mm) were found in the females’ ovaries. Similar to some arrids, C. borneensis is also a paternal mouthbrooder as an important reproductive strategy to protect their offsprings from natural threats. These characteristics are critical in developing ariid species conservation plans, such as setting the time and mesh size for fishing as well as domestication programs in artificial conditions.

Keywords: Arridae catfish, Maturity size, Mouthbrooding, Reproduction, Sexual maturation

PRIMARY PITUITARY CELL CULTURE AS A TOOL TO ESTIMATE THE BIOACTIVE LEVELS OF LUTEINIZING HORMONE AND EXPRESSION VARIATION OF GONADOTROPIN RELEASING HORMONE RECEPTOR AT DEVELOPING GONADAL STAGES OF Chub Mackerel

Sanny David Pacheco Lumayno^ab*, Hirofumi Ohga^a, Sethu Selvaraj^a, Mitsuo Nyuji^a, Akihiko Yamaguchi^a, Michiya Matsuyama^a

^aLaboratory of Marine Biology, Kyushu University, Fukuoka 812-8581, Japan

^bInstitute of Aquaculture, College of Fisheries and Ocean Sciences, University of the Philippines Visayas, Miagao, Iloilo, 5023, Philippines

Corresponding author email address: splumayno@up.edu.ph

Puberty is the time in which reproduction becomes possible for the first time. The brain-pituitary-gonad (BPG) axis is a classical neuroendocrine hormonal pathway regulating reproductive processes, including puberty. The gonadotropin releasing hormone (GnRH) regulation to the synthesis and release of pituitary gonadotropins (GtHs), comprised of follicle stimulating hormone (FSH) and luteinizing hormone (LH), are essential events for pubertal onset. Its action is mediated through GnRH receptor (GnRHR) in the pituitary gonadotrophs. Previous study demonstrated that chub mackerel brain expresses three GnRH forms (gnrh1, gnrh2 and gnrh3), and that only GnRH1 neurons innervated anterior pituitary regions. Furthermore, chub mackerel gnrh1 mRNA exhibits significant increase at the timing of pubertal onset on this species. The present study developed a method on estimating bioactive levels of GtH in cultured medium from the pituitary cells of chub mackerel. Nine pituitaries were excised and diced for enzymatic treatment. Dispersed pituitary cells were then cultured on a 96-well cultured plates at 20˚C in L15 culture medium. After 8 days of culture, cells were exposed for 6 h at different concentrations of the three GnRH ligands. Bioctive levels of LH in culture medium were then estimated through Reporter Gene Assay. Results showed that all three GnRHs stimulated LH release. In addition, gene expression of the GnRH receptor in chub mackerel named as cmgnrhr1 was mainly detected in the pituitary. The cmgnrhr1 expression also showed an increasing trend at developing gonadal stages for both sexes during pubertal process synchronous with the previous study in fsh beta and lh beta gene expression of chub mackerel. This technique has provided an effective way to evaluate LH levels in chub mackerel. Furthermore, the data suggest that cmgnrhr1 is a functionally important receptor to the puberty of chub mackerel.

Keywords: Chub mackerel, Gonadotropin releasing hormone, Gonadotripin releasing hormone receptor, Luteinizing hormone, Puberty, Reproduction

SPECIES AND GENETIC DIVERSITY OF Labiobarbus GENUS IN THE MEKONG DELTA

Damien Habinshuti^1*, Ngoc-Tran Thi Nguyen², Thuy-Yen Duong²

¹International Master’s program in Aquaculture, Can Tho University, Viet Nam

²College of Aquaculture and Fisheries, Can Tho University, Viet Nam

*Corresponding author: habinshuti.damien@gmail.com

Labiobarbus genus (Roberts, 1993), belongs to the family Cyprinidae. This genus is freshwater fish, mainly distributed in several parts of Asia. Due to their morphological similarities, it can be difficult to distinguish between different species, which may result in an inaccurate assessment of species diversity. This study aims to determine the number of species and quantity genetic diversity of the Labiobarbus genus in the Mekong Delta. Samples will be collected in the flooding areas along the Tien and Hau Rivers, including Dong Thap, An Giang, and Can Tho. Species identification will be based on morphological and DNA barcoding methods using the mitochondrial DNA cytochrome c oxidase subunit I (COI) gene. The genetic diversity of collected species will be quantified based on COI data. The study has been on-going. The results will be expected to provide the update information on the number of species of this Labiobarbus genus and their levels of genetic diversity in the Mekong Delta.

Keywords: DNA barcoding, genetic diversity, Labiobarbus genus, species identification

GENETIC DIVERSITY AND POPULATION STRUCTURE OF THE GIANT MOTTLED EEL, Anguilla marmorata IN CENTRAL VIETNAM

Tuan A. Nguyen ^*1, Hoc T. Dao ², Quang T. Hoang ³, Thanh D. Nguyen¹, Seishi Hagihara ⁴, P. Mark Lokman ⁵, Erin L. Damsteegt ⁵

¹ University of Agriculture and Forestry, Hue University, 6 Le Loi Street, Hue city, Vietnam

² Institute of Oceanography, Vietnam Academy of Science and Technology, 01-Cau Da, Nha Trang, Vietnam

³ Institute of Biotechnology, Hue University, Tinh lo 10 Street, Hue city, Vietnam

⁴ Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8564, Japan

⁵ Department of Zoology, University of Otago, 340 Great King Street, PO Box 56, Dunedin 9054, New Zealand

^*Corresponsence: nguyenanhtuan@hueuni.edu.vn

The giant mottled eel, Anguilla marmorata is at high risk of extinction due to overfishing of glass eels and elvers to provide stock for eel farming. In Vietnam, information on the genetic diversity and population structure of this species, which is necessary for resource management, is limited. To address this paucity of information, sequencing of the entire mitochondrial control region (mtDNA) was carried out for 176 individuals collected from central Vietnam. The sequences were investigated using various genetic, phylogenetic and population analyses. A total of 165 distinct haplotypes were identified. The percentage of variation within and among populations was 99.26% and 0.74%, respectively. The fixation index was low (0.007) and not significant (p = 0.096). Therefore, panmixia and a lack of significant population genetic structuring seem likely for A. marmorata in central Vietnam. Most sampled eels were genetically similar to eels found in North Pacific populations (Japan, Taiwan and the Philippines), except for one sample from Quang Tri and two samples from Binh Dinh which had high values of genetic identity (97% to 99%) with South Pacific populations (Tahiti, Fiji, New Caledonia and Papua New Guinea). Taken together, we suggest that A. marmorata from the North and South Pacific populations co-exist in central Vietnam.

Keywords: Anguilla marmorata, panmixia, central Vietnam