Tài liệu Summary of phd thesis pecies composition of gobiidae and eleotridae and biological aspects of some commercial species distributed in the coastal areas of ben tre province

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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 A 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. B 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. 1 + 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. 2 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. 3 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 4 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 5 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). 6 Table 4.1: Thirteen commercial fishes in the study region. No. I 1 2 3 4 II Scientific name TP Eleotridae Butis butis (Hamilton, 1822) Eleotris melanosoma (Bleeker, 1853) Oxyeleotris marmorata (Bleeker, 1852) Oxyeleotris urophthalmus (Bleeker, 1851) 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. Occurrence BT BD + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 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 B. butis E. melanosoma O. marmorata O. urophthalmus A. viridipunctatus B. boddarti G. aureus O. acutipennis P. serperaster P. schlosseri P. elongatus M. chulae T. vagina Ave 14.6 7.45 347 18.7 24.8 24.2 28.4 7.8 28 112 20.8 2 16.5 Weight (g/fish) max min 25 7.5 20 1 900 30 40 10 35 15 50 12 80 10 10 4 50 15 400 5 40 14.5 3 1 20 10 Total length (mm) ave max min 98.4 175 45 48.2 80 10 214 270 120 105 150 30 115 160 75 138 200 100 127 300 75 71 80 50 183 250 110 189 250 100 33.6 200 15 25 30 20 147 200 110 Yield (kg/yr/family) min ave max 373 1092 20 217 700 2 335 2500 10 361 1500 5 1071 2548 50 463 1700 2 809 4500 10 180 700 10 299 1000 2 375 1500 1 811 5000 20 250 300 200 265 576 35 Price (Thousand VND/kg) ave max min 34 60 12 48 110 15 237 400 80 58 80 20 25 40 13 78 110 30 61 100 30 32 60 20 80 135 50 85 135 30 100 135 65 170 250 90 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 7 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). 8 Table 4.3: Fish composition of Gobiidae and Eleotridae families No. Scientific name R 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 Ecology Mu Ma + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 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 9 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 regions No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Scientific name Bostrychus scalaris Oxyeleotris marmorata Oxyeleotris urophthalmus Brachygobius sabanus Eugnathogobius microps Amoya moloana Gobiopsis macrostoma Mugilogobius chulae Periophthalmodon septemradiatus Pseudogobius yanamensis Redigobius chrysosoma Stenogobius mekongensis Stigmatogobius pleurostigma Periophthalmodon schlosseri Periophthalmus variabilis Periophthalmus gracilis Trypauchen vagina Tổng: A + + + + + + + + + + + + + 13 B + + + + 4 *Note: A: seasonal salinity effect areas; B: salinity areas. 4.2.5 The variation of fish composition between fishing gears The fish composition varied with fishing gears due to different feeding habit of fishes, and most of fishes (29/35 species) were caught by gill net and the bag net is the effective gear for mudskipper catching. It could be concluded that gobiids were wide range of salinity as they can live from fresh to marine water. 4.3 Digestive morphology and diet composition of G. aureus 10 and B. boddarti 4.3.1 Digestive morphology 4.3.1.1 Glossogobius aureus This species was carnivore based on its digestive morphology such shape tooth, wide mouth, J-shape stomach, short gut,… and low value of RLG which was 0.26 (<1). 4.3.1.2 Boleophthalmus boddarti This species was herbivore based on its digestive morphology such unshaped tooth, narrow mouth, long gut,… and high value of RLG which was 1.77 (>1). 4.3.2 Diet composition 4.3.2.1 Glossogobius aureus Small crustacean (40.46%) and small fish (46.3%) predominantly occupied the stomach content whereas detritus contributed 12.87% to the diet composition, conforming that this species was carnivorous category based on the scale of Das (1934). Similarly, the goby G. giuris mainly fed on small crustacean and small fish (Pham Thi My Xuan, 2012; Achakzai et al., 2015; Rao and Rao, 2002; Hora, 1935; Mookerjee, 1947). 4.3.2.2 Boleophthalmus boddarti Diatoms (87.84%) were the main prey found in the fish stomach, followed by blue algae (11.31%), indicating that this species was herbivore. In the mangrove forest in Pichavaram, India, this species was also fed mainly on diatoms (Ravi, 2013). This assumption was confirmed by the previous studies of Macnae (1968), Fenchel (1969). Heald and Odum (1970) showed that diatom was the most important prey in the mangrove forest ecosystem. 4.4 Growth of G. aureus and B. boddarti 4.4.1 Length-weight relationship The G. aureus weight ranged from 7.76 g (9.3 cm TL) to 219.95 g (30.1 cm TL), and B. boddarti weight was 7.9–44.2 g (10.3–16.5 cm TL). Both fishes displayed a positive relationship between weight and length. However, the former showed negative isometric growth (W = 0.012*L2.85, R2 = 0.958), whereas the later displayed isometric growth based (W = 0.007*L3.09, R2 = 0.8547) based on the scale provide by Froese (2006). 4.4.2 von Bertalanffy curve 4.4.2.1 Glossogobius aureus Pauly (1987) suggested that the analysis on the structure of a fish 11 population requires at least 1500 fish specimens collected over six months, and the length frequency distribution should display distinct peaks over time. In this study, a total of 2.395 individuals collected during 12 months that adopted to the sampling criteria. The von Bertalanffy curve parameters showed that L∞ = 300 mm; K = 0.77/yr, t0 = -0.02 yr, and total growth parameter Φ’ = 2.84. The longevity of this goby was 3.9 yr that was affected by mortalities (Dinh, 2008). The age and fish length relationship was recorded in Table 4.5 Table 4.5: Age and length relationship of G. aureus. Age 1+ Standard length (mm) 162 2+ 237 + 270 3 4.4.2.2 Boleophthalmus boddarti A total of 6884 individuals collected during 12 months adopting to the sampling criteria was used to obtain the von Bertalanffy parameters (L∞ = 160 mm; K = 0.55/yr and t0 = -0,01 yr) and total growth constant (Φ’ = 2.15). The longevity of this fish was 5.5 yr. The age and fish length relationship was recorded in Table 4.6. Table 4.6: Age and length relationship of B. boddarti. Age 1+ 2+ 3+ 4+ 5+ Standard length (mm) 69 107 130 142 150 The goby G. aureus reached 300 mm in total length at 3.9 year old. Compared to other gobiids, G. aureus grew faster but slower than that of Gobio gobio and Gobius niger (Table 4.7). Froese and Pauly (2015) showed that B. boddarti reach 220 mm TL, but in this study reached 160 mm TL, and this fish grew slowly compared to Periophthalmus babarus (Table 4.7). The variation in the longevity of some gobiids was recorded Table 4.7. 12 Table 4.7: Population parameters of some gobiids. Species Gobio gobio Gobius niger (male) Gobius niger (female) Gobius paganellus Periophthalmus papilio Periophthalmus babarus Pseudapocryptes elongatus Glossogobius aureus Boleophthalmus boddarti L∞ (mm) 106 117 151 138 193,9 216 255 300 160 K (/yr) 0,99 0,91 0,91 0,73 0,51 0,55 0,71 0,77 0,55 t0 Φ’ 0 0,32 0,32 -0,22 n.a n.a -0,09 -0,02 -0,01 2,05 2,1 2,32 2,14 2,28 2,41 2,66 2,84 2,15 Sources Bowker (1996) Vesey và Langford (1985) Vesey and Langford (1985) Azevedo and Simas (2000) Etim et al. (1996) Etim et al. (2002) Tran Dac Dinh et al. (2008) Present study Present study 4.5 Reproductive biology of G. aureus and B. boddarti 4.5.1 Sex ratio The male and female G. aureus ratio was 1:0.93 based on a total of 607 G. aureus (315 males and 292 females) collected during 18 months analysis, indicating that the sex ratio of this goby was close to 1:1 (χ2 = 0.87; p > 0.05). Although the number of female B. boddarti (302) collected was larger than that in males (257), the sex ratio of this fish (1:1.18) was not significant different with 1:1 (χ2, p > 0.5). However, the proportion of female Gobioides rubicundus was higher than that of males in the spawning time (April to July), whereas the revised case occurred post-spawning period (November to December) (Kader et al., 1988). The sex ratio is effected by spawning behaviour like male or female tend eggs (Miller, 1984; Rogers, 1988; Polgar and Crosa, 2009). The similar in the sex ratio of G. aureus and B. boddarti suggested that they shared the same spawning behaviour, or they may not do egg tending. 4.5.2 Gonadal development The goby G. aureus spawned from August to December due to stage IV of gonad mainly appeared in this period, whereas the B. boddarti released eggs monthly as its stage IV of gonad appeared during 12 months. 4.5.3 Gonadosomatic (GSI) and hepatosomatic Index (HSI) 4.5.3.1 Glossogobius aureus Both male and female G. aureus shared the same pattern in the GSI variation. Females’ GSI increased from July and reached a peak in October (8.52±3.77%) before decreasing from November onward and droping to the low point from January to June. By contrast, the HSI was stabled lower point during a period of 4 months (September to 13 December), matching with mature ovaries predominantly appared in that time. 4.5.3.2 Boleophthalmus boddarti The variation in GSI of males was similar to females. The female GSI grew from July to October 2012 and reached the highest point in October 2012 (4.87±3.02%) before declining from November 2012 onward and dropping to the lowest point in January 2013. The GSI of females stabled high value during 4 months (September to December), but HSI reached low point in this period, matching with mature ovaries during this period. Duong Tuan (1981) and Miller (1984) reported that during the maturity period, the energy was stored in muscle and liver, and the energy was supplied for gonad development during the spawning time. It lead to the variation in GSI and HSI of G. aureus and B. boddarti. 4.5.5 Condition factor (CF) The CF of male and female G. aureus varied monthly and increased from November to June and decreased from March to June. Similarly, the CF grew from October to June and declined from March to June in both male and female B. boddarti. The change of gonad weight is one of the factors affecting the variation in CF (King, 1995; Froses, 2006). The low value of CF from January to February of G. aureus CF showed this is the post-spawning time of this gobiid. 4.5.6 Spawning season This goby G. aureus spawned from September to Decmber, releasing mainly eggs in two months (November to December), whereas B. boddarti reproduced during 12 months, laying eggs mostly from October to November based on the GSI, HSI and CF analysis. The high precipitation in rainy season leads to an abundance of food supplied for fish and its fry (Nedeco, 1993; Nguyen et al., 2000; Dinh, 2008). It could result in the spawning season of G. aureus and B. boddarti coincided with the rainy season. 4.5.7 Fecundity The absolute fecundity of G. aureus was 69006±25616 eggs (35175–149932 eggs), and its relative fecundity was 1122±148 eggs/g, whish was higher than that of B. boddarti. The fecundity of B. boddarti was 18.224  2.940 eggs (12.607 – 27.270 eggs), and its relative fecundity was 724  104 eggs/g. The fecundity of fish is species-specific as Eciota lacrimae fecundity was less than 100 eggs (Sunobe and Nakazono, 1995) whereas Awaous guamensis fecundity was higher than 14 500000 eggs (Ha and Kinzie, 1996). The fecundity of two gobiid species in the present study was higher than that of other gobiid such as Neogobius melanostomus (84 – 606 eggs) (Macinnis and Corkum, 2000) Crystallogobius linearis (300 – 700 eggs) (Caputo et al., 2003), Gobius vittatus (560 – 3045 eggs) (Kovačić, 2007), and Periophthalmus papilio (508 – 15,700 eegs) (Lawson, 2011). However, the fecundity of G. aureus and B. boddarti was lower than that Parastromateus niger (71,305 – 3,895,449 eggs) (Dadzie et al., 2008). The goby fecundity of P. elongatus (10,200 – 113,100 eggs) (Dinh, 2008) was higher than that of B. boddarti but lower than that of G. aureus. The diffences in fish fecundity among these gobiids was affected by differences fish size of eggs size of regions (Pham Thanh Liem and Tran Dac Dinh, 2004). 4.5.8 Length at first mature The goby G. aureus reached 142 mm TL for males and 122 mm TL for females at firs mature. The length at first mature of B. boddarti was 128 mm and 126 mm TL for males and females, respectively. Chapter 5: CONCLUSION AND RECOMENDATION 5.1 Conclusion The fish composition of Gobiidae and Eleotridae families in the present study region was high diversity and fishes widely distributed from estuarine to mangrove forest habitats and from fresh to marine water. Of 35 species, 13 commercial fishes were being caught, and P. elongatus and O. marmorata has been farmed. The goby G. aureus was carnivore since small crustaceans and fish were found in its stomach, whereas B. boddarti was herbivore as its stomach contained mainly diatoms and bluealgae. The former showed negative allometric growth whereas the later displayed isometric growth and both these fishes belonged to fast growth pattern category, suggesting that they were potential fish for future aquaculture. The sex ratio of two gobiid species in this study was close to 1:1. They were multiple-spawner laying eggs mainly in the main rainy season. The goby G. aureus reached 142 mm TL for males and 122 mm TL for females at firs mature. The length at first mature of B. boddarti was 128 mm and 126 mm TL for males and females, respectively. 5.2 Recommendation - There was a need to find the suitable method to conserve the fishery resources of E. microps and G. macrostoma due to few fish caught. 15 - The length at first capture should be higher than 142 mm and 128 mm TL for G. aureus and B. boddarti for future sustainable exploitation and management. - Future artificial aquaculture and reproduction of G.aureus and B. boddarti should be conducted based on initial knowledge on its feeding habit and reproductive biology. 16 PUBLICATIONS Journal 1. Nguyen Minh Tuan, Tran Dac Dinh, Nguyen Hoai Anh, Tran Trung Kien and Hoang Lam Truc, 2013. The species composition of goby (Gobiidae and Eleotridae) and some feeding, reproductive biology characteristics of the goby Boleophthalmus boddarti (Pallas, 1770), in the Bentre coastal areas. Science and Technology Journal of Agriculture & Rural Development, (12/2013): 175-182. 2. Nguyen Minh Tuan, Huynh Thi Ngoc Lanh, Nguyen Thanh Phuong and Tran Dac Dinh, 2014. Some Biological Characteristics Of The Glossogobius aureus Akihito and Meguro, 1975 Distributed In Ben Tre Province, Journal of Science, Can Tho University (2014): 169-176. Conferences 1. Nguyen Minh Tuan, Tran Dac Dinh, Nguyen Hoai Anh, Tran Trung Kien and Vo Hoang Lam Truc, 2013. The species composition of goby (Gobiidae and Eleotridae) and some feeding, reproductive biology characteristics of the goby Boleophthalmus boddarti (Pallas, 1770), in the Bentre coastal areas. National Scientific Workshop on marine fisheries in 2013, Hai Phong November 2013. 2. Nguyen Minh Tuan, Huynh Thi Ngoc Lanh, Nguyen ThanH Phuong and Tran Dac Dinh, 2014. Some Biological Characteristics Of The Glossogobius aureus Akihito and Meguro, 1975 Distributed In Ben Tre Province, Aquatic Science Meeting times V in Can Tho University August 2014. 3. Nguyen Minh Tuan, Tran Dac Dinh, 2014. Species Composition of Gobiidae và Eleotridae and Some Biological Aspects of Glossogobius aureus Akihito and Meguro, 1975 Distributed in The Coastal Areas Of Ben Tre Province, Mekong Delta, Vietnam. International Fisheries Symposium 2014 “Development of Fisheries and Marine Technology for Sustainable Biodiiversity Conservation and Respoonsible Aquacuture Industries”. Surabaya, Indonesia. October 3031th, 2014. 6-O-18. 17
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