Tóm tắt Luận án Species composition of gobiidae and eleotridae and biological aspects of some commercial species distributed in the coastal areas of Ben Tre province

A MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY SUMMARY OF PhD THESIS Major: Aquaculture Major code: 62620301 NGUYEN MINH TUAN SPECIES COMPOSITION OF GOBIIDAE AND ELEOTRIDAE AND BIOLOGICAL ASPECTS OF SOME COMMERCIAL SPECIES DISTRIBUTED IN THE COASTAL AREAS OF BEN TRE PROVINCE Can Tho, 2016 B THIS STUDY HAS BEEN COMPLETED AT CAN THO UNIVERSITY Supervisor: Assoc. Prof. Dr. Tran Dac Dinh The thesis was confirmed at the defence committee of Can Tho University Venue: . Time: . Reviewer 1: Reviewer 2: Reviewer 3: This thesis is available at: Learning Resource Centre, Can Tho University. Vietnam National Library. 1 Chapter 1: INTRODUCTION 1.1 General introduction In the Mekong Delta, the fish composition of Gobiidae and Eleotridae is high diversity with 66 species living from fresh to marine water (Tran Dac Dinh et al., 2013). Of these fishes, Glossogobius giuris, Oxyeleotris urophthalmus, Boleophthalmus boddarti are important commercial fishes for food and are widely distributed from inland to estuarine regions (Murdy, 1989; Clayton, 1993) and from tropical to subtropical areas (Chotkowski et al., 1999, Blaber et al., 2000). Boleophthalmus boddarti (Pallas, 1770) and Glossogobius aureus Akihito and Megugo, 1975 are two commercial fishes that contribute to the local fisheries products. The coastline of Ben Tre Province is the downstream of Tien River comprise four estuaries with large areas of muddy flats. The gobiids of Gobiidae and Eleotridae are important for food in this region, but there has been little published work on these fishes. Therefore, this study was conducted to provide useful information on gobiid composition and biological characteristics that will be a basis for sustainable exploitation of the gobiid resources in the region. 1.2 Study objectives - General objectives: determine the fish composition and biological characteristics of gobies (Gobiidae and Eleotridae) using for fishery management and sustainable development in the Mekong Delta in generally and Ben Tre Province in specifically. - Specific objectives: + Contribute to the fish composition of Gobiidae and Eleotridae families along the coastline of Ben Tre Province. + Provide new information on food and feeding habit, growth and reproductive biology of Glossogobius aureus Akihito and Megugo, 1975 and Boleophthalmus boddarti (Pallas, 1770). 1.3 Study contents - Investigate the fisheries status and economic species of Gobiidae and Eleotridae families along the coastal areas of Ben Tre Province. - Determine the species composition of Gobiidae and Eleotridae families along the coastline of Ben Tre Province. - Determine some biological characteristics of Glossogobius aureus and Boleophthalmus boddarti, including: + Digestive morphology characteristics and diet composition. 2 + Growth pattern: length-weight relationship and von Bertalanffy curves. + Reproductive biology: gonadal stage, sex ratio, gonadosomatic (GSI), hepatosomatic (HSI), condition factor (CF), fecundity, spawning season and length at first mature (Lm). 1.4 The significance of the thesis The results update the basic knowledge about the species composition of Gobiidae and Eleotridae distributed in coastal mudflats, status of fisheries and important comercial species; findings on biological characteristics of growth and reproduction of G. aureus and B. boddarti. The results can be applied for artificial breeding for aquaculture development of G. aureus, B. boddarti in the coastal areas. 1.5 The Significant Results - The species composition of Gobiidae and Eleotridae distributed in coastal areas in Ben Tre Province are 35 species, including 28 species of Gobiidae (80%) and 7 species of Eleotridae (20%). - There are 13 important commercial species of Gobbiidae and Eleotridae. - The results provide some biological characteristics of G. aureus and B. boddarti include: + G. aureus have digestive organs morphology suitable for fish species, animal feed and feed ingredients common crustacean and small fish predominate (86.8%); meanwhile, B. boddarti have digestive organs morphology consistent with herbivorous species and common properties of food ingredients dominant diatom (87.84%). +Length-weight relationship showed that G. aureus grows allometrically, meanwhile B. boddarti grows isometrically. The results also showed the growth parameters of G. aureus are L∞ = 300 mm; K = 0.77 / year and t0 = -0.02 years, and thoese of B. boddarti are L∞ = 160 mm; K = 0.55 / year and t0 = -0.01 years; which can be identified the relationship between length and age of those species. + Results showed that spawning season of G. aureus and B. boddarti in the rainy season, the absolute fecundity are high and fecundity G. aureus is higher than of B. boddarti. Determine the length at first maturity to help fishermen to catch fish larger than the length at first maturity in order to maintain the fish populations. 3 Chapter 3: MATERIALS AND METHODS 3.1 Methods 3.1.1 Time and region study Fish specimens were collected from 4/2012 to 3/2014 along the coastal areas of Ben Tre Province (downstream of Tien River). The pH and salinity were also recorded. Specimen analysis: at the field and the Laboratory of Fisheries Resources, College of Aquaculture & Fisheries, Can Tho University. 3.1.2 Materials Fishing gear: gill net, bag net and others; camera, macroscopic and microscopic, GPS (Global Positional System); electronic scale, ruler and fish surgery equipment; thermometer (pH–506) and refractometer (TI–SAT100(A)); formalin, alcohol (70%) and other chemicals. 3.2 Study 1: Investigate the fishing status of fish species of Gobiidae and Eleotridae along the coastal areas of Ben Tre Province. 3.2.1 Time and study areas: information on fishing status of gobiids was collected from 3/2012 to 4/2012 at 3 districts such as Binh Dai (30 samples), Ba Tri (30 samples) and Thanh Phu (30 samples). 3.2.2 Data collection method: the questionnaire was used to obtain the fishing status from fisherman based the method of Froese and Pauly (2012). 3.2.3 The content of questionnaire - Species composition; - Fishing gears, size of fishing species (g/fish); - Yield (kg/yr); price (VND/kg); - Fishingground; - Fishing season (month); - The change of yield compared to 5 yrs ago (±%). The main reason lead to the variation of each fish yield; - Potential fish species for aquaculture. 3.3 Study 2: Species composition determination. 3.3.1 Fish collection and fixation Collection Specimens were monthly collected from 4/2012 to 12/2013 using gill and bag nets at the muddy flat and mangrove forest along the coastal areas of Ben Tre Province. 5-10 specimens/species were used for identification; and the temperature, pH and salinity were also recorded. 4 Fixation Specimens were fixed using formalin (10%) after collection before transport to the Laboratory of Fisheries Resource, College of Aquaculture & Fisheries, Can Tho University for analysis. 3.3.2 External determination Fish external was determined based on the method of Pravdin (1973). The fish taxonomy was identified using the taxonomic suggested by Froese and Pauly (2015). 3.4 Study 3: The digestive morphology determination for G. aureus and B. boddarti. 3.4.1 Fish collection and fixation Time and study area: + Glossogobius aureus: this study was conducted from 1/2013 to 12/2013 at Thanh Phu. + Boleophthalmus boddarti: this study was conducted from 4/2012 to 3/2013 at Ba Tri. Number of specimens: + Glossogobius aureus: 411 individuals and 35 individuals were used for length-weigh relationship analysis and diet composition analyses, respectively. + Boleophthalmus boddarti: 436 individuals and 30 individuals were used for length-weigh relationship analysis and diet composition analyses, respectively. The gill nets with 15 mm mesh size of the cod end (2a) were used to collect G. aureus, whereas the bag nets used to collect the B. boddarti. Fish were fix in formalin (10%) after collection and transport to the Laboratory of Fisheries Resource, College of Aquaculture & Fisheries, Can Tho University for analysis. 3.4.2 Specimen analysis 3.4.2.1 Digestive morphology and structure: Fish tooth, mouth, structures were observed, and the gut and fish length ratio (was calculated based on the method of Al-Hussainy (1949). RLG = gut length (cm)/fish length (cm) 3.4.2.2 Diet composition: The occurrence and gravimetric methods were applied for G. aureus, whereas the occurrence and point methods were used for B. boddarti based on the method of Biswas (1993). 3.5 Study 4: Growth pattern of G. aureus and B. boddarti 3.5.1 Length-weight relationship 5 W = a*Lb (Jennings et al., 2001) where: W: fish weight (g); L: total length (cm); a: initial growth constant; b: growth parameter. 3.5.2 The von Bertalanffy growth equation The parameters (L, K and to) of the von-Bertalanffy equation were determined using FiSAT II software based on the 12-month length frequency data (Gayanilo et al., 2006). Lt = L (1-e-K (t-to)) where: Lt : the length of fish at t age L∞: asymptotic length; t0: the age at which egg is fertilised; K: growth parameter. * The index of growth performance: Φ’ = logK+2log L (Pauly and Munro, 1984). * The longevity (tmax): tmax = 3/K (Taylor, 1958): 3.6 Study 5: The reproductive biology of G. aureus and B. boddarti A total of 607 G. aureus and 559 B. boddarti were collected monthly during a period of 18 months were used for this study. Gonadal development determination * The gonadal development was determined based gonads’ external and histologically based on the method of Nikolsky (1963). * The gonadal histologically was done based method of Drury and Wallington (1980) and Gabe (1976). The development of oocytes was determined based on scale of Pham Quoc Hung et al. (2014). Sex ratio determination Fish specimens were sexually differentiated based the external morphology of gonads that were removed from specimens after surgery. The sex ratio was calculated as: Sex ratio = number of females/number of males Gonadosomatic index: GSI (%) = (GW/W)*100 where: GW: gonad weight (g); W: fish weight (g). Hepatosomatic index: HSI (%) = (LW/W)*100 6 where: LW: liver weight (g); W: fish weight (g). Condition factor: CF = W/Lb (King, 1995) where: W: fish weight (g); L: total length (cm); b (growth parameter) and a (initial constant) obtained from length-weigth relationship; Spawning season The spawning season was determined based on the variation of GSI, HSI and CF. Fecundity * Absolute fecundity (F): F = (n*G) /g where: F: fecundity; G: gonad weight (g); g: representative gonad weight (g); n: number of eggs in the representative gonad weight. * Relative fecundity Relative fecundity (egg/g) = absolute fecundity/weight of fish) Length at first mature (Lm) The length at first mature is the length at which 50% fish reach maturity (King, 2007): P = 1/{1+exp[-r(L-Lm)]} where: P: Proportion of maturity; r: relative constant; L: mean of fish length; Lm: length at first mature. 3.7 Data analysis Mean, standard deviation, max, min and χ2 test were performed using Excel. FiSAT II (FAO) was used to obtain the von Bertalanffy curve parameters, and Lm determined using STATISTICA 8.0. Chapter 4: RESULTS AND DISCUSSION 4.1 The fishing status of Gobiidae and Eleotridae families in Ben Tre Province. 4.1.1 Fish species composition Thirteen commercial fish species of Gobiidae (9) and Eleotridae (4) families has been caught in the study region (Table 4.1). 7 Table 4.1: Thirteen commercial fishes in the study region. No. Scientific name Occurrence TP BT BD I Eleotridae 1 Butis butis (Hamilton, 1822) + + + 2 Eleotris melanosoma (Bleeker, 1853) + + + 3 Oxyeleotris marmorata (Bleeker, 1852) + + + 4 Oxyeleotris urophthalmus (Bleeker, 1851) + + + II Gobiidae 5 Acentrogobius viridipunctatus (Valenciennes, 1837) + + 6 Boleophthalmus boddarti (Pallas 1770) + + + 7 Glossogobius aureus Akihito & Meguro, 1975 + + + 8 Oligolepis acutipennis (Valenciennes, 1837) + 9 Parapocryptes serperaster (Richardson, 1846) + + 10 Periophthalmodon schlosseri (Pallas 1770) + + + 11 Pseudapocryptes elongatus (Cuvier, 1816) + + + 12 Mugilogobius chulae (Smith, 1932) + 13 Trypauchen vagina (Bloch & Schneider, 1801) + *Note: TP:Thanh Phu; BT:Ba Tri; BD: Binh Dai. 4.1.2 Fishing status and economic values The information on fishing status and price of 13 commercial fishes based on the survey of 90 fishermen (Table 4.2). Table 4.2: Fishing status and economic values of 13 fish species. Species Weight (g/fish) Total length (mm) Yield (kg/yr/family) Price (Thousand VND/kg) Ave max min ave max min ave max min ave max min B. butis 14.6 25 7.5 98.4 175 45 373 1092 20 34 60 12 E. melanosoma 7.45 20 1 48.2 80 10 217 700 2 48 110 15 O. marmorata 347 900 30 214 270 120 335 2500 10 237 400 80 O. urophthalmus 18.7 40 10 105 150 30 361 1500 5 58 80 20 A. viridipunctatus 24.8 35 15 115 160 75 1071 2548 50 25 40 13 B. boddarti 24.2 50 12 138 200 100 463 1700 2 78 110 30 G. aureus 28.4 80 10 127 300 75 809 4500 10 61 100 30 O. acutipennis 7.8 10 4 71 80 50 180 700 10 32 60 20 P. serperaster 28 50 15 183 250 110 299 1000 2 80 135 50 P. schlosseri 112 400 5 189 250 100 375 1500 1 85 135 30 P. elongatus 20.8 40 14.5 33.6 200 15 811 5000 20 100 135 65 M. chulae 2 3 1 25 30 20 250 300 200 170 250 90 T. vagina 16.5 20 10 147 200 110 265 576 35 24 35 13 There are many types of fishing gear such as gill net, bag net, trawl net, casting net, and hook and line were used to catch fishes. Of them, bag net was the main fishing gear for mudskipper catching at the muddy flat whereas other fishes were caught by other gears. Nguyen Bach Loan (2003) reported that mudskippers had sub-respiration organs that enable 8 they can move on the mud regions (Macnae, 1968; Clayton and Vaughan, 1988). Oxyeleotris marmorata was the largest size ranged from 347 g (214 mm in TL) to 900 g (270 mm in TL) among these species, and it is the most important fish and currently aquaculture in Ben Tre Province, whereas Acentrogobius viridipunctatus and Trypauchen vagina were low price. Although the goby G. aureus and B. boddarti cost from 60.000 VND/kg and 80.000 VND/kg respectively, their yield was high. They were also potential aquaculture fish due to high demand for food, especially G. aureus has been farming in some extensive shrimp at Thanh Phu district. However, the yield of this fish was low since the fry or juvenile were collected from the wild in the Mekong Delta. Therefore, there is a need to study on the reproductive biology of G. aureus that will be a basis for artificial reproductive study supplying the fry for aquaculture. Comparing to 5 years ago, the yield of 13 commercial fishes decreased gradually due to high exploitation, suggesting that aquaculture for gobiids was the fundamental demand. Among these fishes, P. elongatus and O. marmorata have been farming in this region and G. aureus and B. boddarti were two potential fish for future aquaculture. 4.2 Environmental factors and fish composition of Gobiidae and Eleotridae families in Ben Tre Province. 4.2.1 Environmental factors The temperature and pH were not significantly different between seasons whereas the salinity was dramatically higher in the dry that in the rainy season. In the annual salt effect regions, salinity increased gradually from 12/2012 to 3/2013 reaching the highest point of 28±1‰, but there was a downtrend of salinity from 4/2012 onward and dropping the lowest point of 8±2,7‰. In the seasonal salt effect, the salinity grew to 14,2±4‰ from 1/2013 to 3/2013 after decreasing from 5/2012 onwards and stabilising at 0‰ during a period of 5 months (8/2012 – 12/2012). The variation of salinity caused by the heavy precipitation in the rainy season and the intrusion of marine water to freshwater in the dry season. The change in salinity was one of the factor lead to the diversity of fish composition in this study area. 4.2.2 Fish composition A total of 35 species belonging to 24 genera was recorded in the study region (Table 4.3). 9 Table 4.3: Fish composition of Gobiidae and Eleotridae families No. Scientific name Ecology R Mu Ma I Eleotridae 1 Bostrychus scalaris Larson, 2008 + 2 Butis butis (Hamilton, 1822) + + 3 Butis humeralis (Valenciennes, 1837) + + 4 Butis koilomatodon (Bleeker, 1849) + + 5 Eleotris melanosoma Bleeker, 1853 + 6 Oxyeleotris marmorata (Bleeker, 1852) + 7 Oxyeleotris urophthalmus (Bleeker, 1851) + II Gobiidae 8 Acentrogobius canius (Valenciennes, 1837) + 9 “Acentrogobius” globiceps (Hora, 1923) + + 10 Acentrogobius viridipunctatus (Valenciennes, 1837) + + + 11 Amoya moloana (Herre, 1927) + 12 Aulopareia unicolor (Valenciennes, 1837) + + 13 Boleophthalmus boddarti (Pallas 1770) + 14 Brachygobius sabanus Inger, 1958 + 15 Caragobius urolepis (Bleeker, 1852) + 16 Eugnathogobius microps Smith, 1931 + 17 Glossogobius aureus Akihito & Meguro, 1975 + 18 Glossogobius giuris (Halminton, 1822) + 19 Glossogobius sparsipapillus Akihito & Meguro, 1976 + 20 Gobiopterus chuno (Hamilton, 1822) + + 21 Gobiopsis macrostoma Steindachner, 1861 + 22 Mugilogobius chulae (Smith, 1932) + 23 Oligolepis acutipennis (Valenciennes, 1837) + 24 Parapocryptes serperaster (Richardson, 1846) + 25 Periophthalmodon schlosseri (Pallas, 1770) + 26 Periophthalmodon septemradiatus (Hamilton, 1822) + 27 Periophthalmus variabilis Eggert, 1935 + + 28 Periophthalmus gracilis Eggert, 1935 + + 29 Pseudapocryptes elongatus (Cuvier, 1816) + 30 Pseudogobius yanamensis (Rao, 1971) + + 31 Redigobius chrysosoma (Bleeker, 1875) + 32 Stenogobius mekongensis Watson, 1991 + 33 Stigmatogobius pleurostigma (Bleeker, 1849) + + 34 Taenioides gracilis (Valenciennes, 1837) + 35 Trypauchen vagina (Bloch & Schneider, 1801) + *Note: R: River; Mu: Muddy flat; Ma: Mangrove forest Gobiidae family with 28 species and 20 genera mainly contributed to fish composition in the present study region (80%), which was 4 times higher than that of Eleotridae family (7 species and 4 genera, 20%). These fishes widely distributed from estuarine to mudflat and mangrove forest regions, but Boleophthalmus boddarti và Periophthalmodon schlosseri mostly occurred at the muddy and mangrove forest habitats. 4.2.3 The variation of fish composition between seasons 10 The fish composition was more diversity (35 species) in the rainy season than in the dry season (22 species). Gobiidae family displayed more variation in fish composition compared to Eleotridae family between dry and rainy seasons. In the dry season, B. scalaris, A. globiceps, A. viridipunctatus, A. unicolor, B. sabanus, E. variegates, G. macrostoma, P. yanamensis, R. chrysosoma, S. mekongensis, S. pleurostigma, T. gracilis, T. vagina were not found, resulting from the difference in salinity and prey items in the environment. 4.2.4 The variation of fish composition between habitats The fish composition was high diversity in the seasonal salt effect region (31/35 species) than in the annual salt effect region (22/35 species). Some species was only found in the later region as they were brackish species that cannot live in the former area (Table 4.4). Table 4.4: Species only found at the seasonal or annual salt effect