Early Development Of Mudskippers And Its Effect On The Tidal Marshes

Mudskippers (Perciformes: Gobiidae) widely habitat in the mudflat and mangroveecosystems of the Ind-Pacific and the Atlantic coast of Africa, which are small inindividuals. Mudskippers are consist of31species including4genus (18speciesincluding Periophthalmus,3species including Periophthalmodon,6species includingBoleophthalmus and4species inlcluding Scartelaos).There are6species mudskippersof3genus (Periophthalmus, Boleophthalmus and Scartelaos) distributing on the tidalmarshed from Bohai bay to Hainan island in China. Periophthalmus is consist of P.modestus, P. argentilineatus and P. magnuspinnatus, Boleophthalmus contain1speciesB. pectinirostris, Scartelaos is consist of S. viridis and S. gigas.Mudskippers play an important part in the biodiversity of wetlands, whichcommunity structure and dynamic changes reflect the stability and health of wetlands.Hangzhou Bay Wetland as the transition zone of coastal wetlands in China, lies in thewest part of Hangzhou Bay Sea-crossing Bridge and has many advantages indeveloping tourism resources and protecting the biodiversity. But there are rarelyresearches about the food web of the south bank of Hangzhou Bay Wetland and thebiology of the mudskippers.In this paper, embryonic development and post-embryonic development wereobserved, and the effect of temperature and salinity on embryonic development wasdiscussed. The study showed the food sources and trophic levels of mudskippers on thetidal marshes in south bank of Hangzhou Bay and illuminated the characters of the tidalmarsh.The main results were as follows:1. The ratio of female and male was4.6:1of P. magnuspinnatus on the tidalmarshes in south bank of Hangzhou Bay, the range of the total length (TL) was5.7-8.4cm (average7.56cm), the range of body weight (BW) was2.60-5.83g (average4.72g).Fertilized eggs were got through a semi-dry artificial fertilization method and werecultured in constant temperature in seawater with weak aeration. The individualabsolute fecundity (F) ranged from2249to3472eggs, with an average of2746eggs.The individual relative fecundity per millimeter (FL) ranged from32to44(average35)eggs per millimeter and the individual relative fecundity per gram (FW) ranged from643to1320(average698) eggs per gram. After Injection of LHRH-A3(luteinizing hormone releasing hormone-analogue)0.2μg and HCG20IU into female fish and HCG20IU intomale, most of experimental fish were able to develop to mature. Under the watertemperature (27℃), salinity (10) and pH (7.8±0.3), the embryonic development required158h46min and accumulated temperature was up to4286.7h℃. Before hatchs theorgans are normally differentiated, such as distinct gut, visible anus, and air bladderelliptical in shape, melanophore of eyes and283/min of heart beating. The optimumtemperature for embryo development is24-30℃, and the time of embryo developmentwas negative correlative with incubation temperatures. The fertilized eggs can notachieve the embryonic development in the higher and lower incubation temperatures(32℃,20℃and22℃), and died in the embryo formation stage.The optimum salinityfor embryo development is5-15. Under high salinity concentrations (35,30,25and20),the fish larvae were not be hatched from the fertilized eggs.2. The ratio of female and male was4.8:1of P. modestus on the tidal marshes insouth bank of Hangzhou Bay, the range of the total length (TL) was4.4-7.3cm (average6.47cm), the range of body weight (BW) was2.36-5.35g (average4.22g). Embryonicdevelopment was characterized by continual viviperception. The results indicated that Franged from1432to2978eggs, with an average of1998eggs (n=83). The individualrelative fecundity per millimeter (FL) ranged from36to62eggs (average45eggs) andthe individual relative fecundity per gram (FW) ranged from528to1530eggs (average864eggs, n=83). The Gonadosomatic Indexes (GSI) for female and male were8.47%-25.39%(average14.49%, n=83) and0.10%-0.57%(average0.25%, n=76),respectively. The fertilized eggs were demersal with adhesive filaments and elliptical inshape (0.75±0.02mm and0.56±0.01mm in long-axis and short-axis diameter,respectively (n=300)). At the water temperature of27±0.5℃, salinity of10and pH of7.8±0.3, the embryonic development required124.13h and the accumulatedtemperature was up to3351.51h℃. Before the larvae were hatched, the organs hadalready differentiated normally, such as distinct gut, visible anus, air bladder elliptical inshape, and melanophore of eyes. The heart rate could up to154.33±5.87per minute(n=20). Newly hatched larvae (2.17±0.09mm in total length, n=9) possessed a yolk sac(0.98-1.87mm in diameter, n=9). The larvae completely absorbed the yolk and startedfeeding at the third to fourth day after hatching at the water temperature of27±0.5℃;eleven days after hatching, the tail notochord of larvae became askew up; the upper andlower jaw teeth occurred at eleven and fifteen days after hatching, respectively;twenty-three days after hatching, all fins except the first dorsal fin had been formed. Atthe whole course, the larvae were feeding on rotifers (Brachionus plicatilis) with thesize0.038-0.074mm. There were two death peaks, the first death peak was five to seven days after hatching, the reason was the larvae cannot eat the food; the second wastwenty to twenty-three days after hatching, the reason was the larvae was in the periodof metamorphosis and it cannot fit the circumstance and get the suitable food.3. The ratio of female and male was2.0:1of B. pectinirostris on the tidal marshesin south bank of Hangzhou Bay, the range of the total length (TL) was8.6-13.3cm(average10.47cm), the range of body weight (BW) was10.36-21.35g (average17.24g). Mature testis was milk-white thin strips, the left and right sides testis is symmetrical,the length was3.3±0.56cm. Seminal vesicle was wing structure and had melanophoresdistributing on it, the belly of mature female fish was swollen and soft, gonopore wasred and protruding. The optimum temperature for embryonic development of B.pectinirostris is24-30℃, during these incubation temperatures, the embryodevelopment time is132.10-215.18h. The optimum salinity for embryo development ofB. pectinirostris is5-15. The total length (TL) of newly hatched larvae is (2.67±0.09)mm，cleft length (CL) is0.135mm. Larvae begin to eat B. plicatilis about4-5days afterhatching at water temperature27±0.5℃, the TLof lavae is3.10-3.22mm at this pointand the corresponding CL is0.18-0.19mm. the larvae were cultured11d.4. C4plant Spartina alterniflora contributed96%and86%of total organic carbonof B. Pectinirostris and S. viridis. C4plant S. alterniflora contributed44%and50%oftotal organic carbon of P. magnuspinnatus and P. modestus. So C4plant S. alterniflorawas the primary organic carbon sources for four mudskippers. The trophic levels of fourmudskippers were3.03-3.97in autumn, P. modestus occupied the highest trophic level(3.97), B. pectinirostris occupied the lowest trophic level (3.03), P. magnuspinnatus andS. viridis occupied the intermediate trophic level (3.94and3.38). There was nosignificantly difference in the trophic levels of four mudskippers during the differentseasons (P>0.05). P. magnuspinnatus and P. modestus were carnivorous, the adult of P.magnuspinnatus prefered to crabs, and P. modestus mainly feeded on polychaetes, B.Pectinirostris was herbivorous, mainly feeded on benthic diatoms, S. viridis wasomnivorus, the TL of the four mudskippers were consistent with its diets. Overall, P.modestus and P. magnuspinnatus occupied higher trophic position, S.viridis and B.Pectinirostris occupied lower trophic position.5. S. alterniflora, a C4plant, had a significantly more enriched δ13C value(-13.48±0.17‰) than other primary producers (P<0.05), C3plants S. mariqueter(-28.10±0.28‰) and P. australis (-27.76±0.46‰) had most depleted δ13C values，andthere was no significantly difference in the δ13C values of those two kind plants(P>0.05). The δ13C values of benthic microalgae, surface sediment organic matter andparticulate organic matter were intermediate. The stable nitrogen isotope ratiosindicated a total of three trophic levels on the tidal marsh food web in south bank of Hangzhou Bay. The lowest TL of consumers was2.0, the corresponding species wasBullacta exarata, and the highest TL of consumers was3.97, the corresponding specieswas Odontamblyopus lacepedii.14species macroinvertebrates and1species fish wereprimary consumers, its corresponging TL range was2.00-2.91;8speciesmacroinvertebrates and7species fishes were secondary consumers, its correspondingTL range was3.03-2.91;4species fishes occupied the highest TL (3.97), those speciewere O. rubicundus、Acanthogobius ommaturus、P. magnuspinnatus and P. modestus.The TL of macroinvertebrates ranges from2.00to3.66, most macroinvertebrates(64.0%) ocupped the primary consumers (TL2). The TL of fishes ranges from2.82to3.97, most of fishes (91.2%) represented the secondary consumers (TL3). The δ15Nvalues of co-ocurred species in south bank of Hangzhou Bay were enriched than in theYangtze River estuary and Yancheng coastal wetlands, this result indicated thatHangzhou Bay was more eutrophic.