Feeding Ecology And Ontogenetic Development Of The Digestive System Of Squaliobarbus Curriculus Larvae

Spualiobarbus Curriculus belongs to Cyprinidae.It is an important eurythermic and economic fish species,which lives in the upper water.Its reproductive season usually lasts from May to August.Due to the unstable survival rate and the increase of the market demand,we explored the phytoplankton community structure of cultivating pond of S.Curriculus fingerlings and feeding habits along with the growth of the larvae.Meanwhile the histologically development of the digestive organs and the activities of digestive enzymes AMS(amylase),TRY(trypsin),LPS(lipase),ALP(alkaline phosphatase)and pepsin of the larvae were analyzed.Such information will establish theoretic basic for improving the survival rate of S.Curriculus larvae.1.The dynamic characteristics of the plankton community in the ponds of S.Curriculus larvae.The pond used for cultivation of S.Curriculus fingerlings was selected for analyzing plankton community structure.Shannon-Wiener diversity index(H'),Pielou evenness index(J),Margalef richness index(d)and Mcnaughton dominance index(Y)were directed.A total of 119 species of the phytoplankton were collected: 13 species of Cyanophyta,60 species of Chlorophyta,18 species of Euglenophyta,10 species of Bacillariophyta,7 species of Chrysophyta,6 species of Pyrrophyta,5 species of Xanthophyta.A total of 105 species of zooplankton were detected: 47 species of Protozoa,46 species of Rotatoria,5 species of Cladocera,7 species of Copepoda.The abundance of phytoplankton ranged from 51.6 × 104 to 669.07 × 104 cells /L.The biomass of phytoplankton ranged from 0.99 to 5.04 mg/L.The abundance of zooplankton ranged from 220 to 25080 ind./L.The biomass of zooplankton ranged from1.171 to 35.374mg/L.The main dominant species of phytoplankton were Oscillatoria repens of Cyanophyta,then followed by Chlorella of Chlorophyta,pirulina,Coccomyxa Schmidle and Actinastrum hantzschii.The dominant species of zooplankton species were Pompholyx complanata,then followed by Branchionus leydign,Keratella valga,Holophrya vesiculosa,Aspidisca sp.Vorticella sp.,and Onychocamptus mohammed was the dominant species in the last sampling period.The Shannon-Wiener diversity index of phytoplankton changed from 1.8 to 4.42 with an average of 3.22.The evenness index of phytoplankton changed from 0.42 to 0.88 with an average of 0.67.The Richness index of phytoplankton changed from 1.76 to 4.18 with an average of 2.95.The Shannon-Wiener diversity index of zooplankton changed from 0.14 to 3.62 with an average of 2.39.The evenness index of zooplankton changed from 0.04 to 0.93 with an average of 0.57.The Richness index of zooplankton changed from 0.89 to 3.49 with an average of 2.42.In general,the diversity index of phytoplankton in the pond was higher than that of zooplankton.Phytoplankton community structure is relatively stable.2.Feeding habits and growth of S.Curriculus larvaeA regression analysis was performed on the total length and weight of the S.Curriculus larvae from hatching to 30 days post hatching(dph).The results showed that the specific growth rates of the total length and weight were 6.99% and 22.26%,respectively.The relationship between the total length(L/mm)and the age(D/ d)was L=5.081e0.07D(R2=0.91),the relationship between weight(W/g))and the age(D/ d)was W=0.905e0.235D(R2=0.897)and the relationship between weight(L/mm)and the age(W/g)could be expressed as W=0.004L3.381(R2=0.995).Studies on food composition and food selectivity in early stage of S.Curriculus larvae were conducted.Diet occurrence frequencies of larvae from high to low were Spirulina sp.,Microcystis sp.,Coccomyxa actinabiotis,Chlorella vulgaris,Cladophora sp.,and the proportion of Spirulina sp.,Microcystis sp.was higher,accounting for 57%and 47.67%.According to the analysis of diet composition,it was found that the main food was Cyanophyta and Chlorophyta on 4 dph,and the percentage of food was 73%and 27% respectively.The proportion of Cyanophyta and Chlorophyta were still high on5 dph,ratios of which were 55% and 45% respectively.The number of Cyanophyta increased,including Microcystis sp.,Spirulina and Oscillatoria and Chlorella of Chlorophyta increased.The proportion of Chlorophyta was increased to 57% on 6 dph,and the newly added species of Chrysophyta and Pyrroptata were 1.6% and 0.4%respectively.Organic detritus accounted for a large proportion of the food composition on 15 dph,with 55.5% of the food,followed by Cyanophyta and Chlorophyta,which accounted for 33% and 10.1% respectively.Food selectivity index analysis showed that larvae had strong preference to Microcystis sp.and Chlorella sp.on 4 dph.The larvae prefered Spirulina sp.and Coelosphaerium sp.to Microcystis sp.,Dinobryor sp.and Chlorella sp.on 6 dph.It began to choose rotifers on 8 dph and species and quantities of diets increased from 15 dph.Artificial feed became the major food source of larvae from 20 dph.3.Histologically development of the digestive organs in S.Curriculus larvaeOntogenetic development of the digestive system of S.curriculus larvae was studied histologically during 0-30 dph with paraffin section technique.The results showed that: larval development of S.curriculus could be divided into three phases:phase I(endotrophic period): 1–3 dph;phase II(endo-exotrophic period): 4–5 dph;and phase III(exclusively exotrophic period): from 6 dph onward.On 2 dph,the mouth had opened,connected with the esophagus,and larvae depended on the yolk sac for nutrition.On 4 dph,the anus had opened and the larvae started feeding.On 6 dph,the yolk sac was completely exhausted and digestive system differentiated obviously into esophagus,intestine,liver and pancreas.On 15 dph,intestinal folds increased distinctly and the striated border was obvious in the intestine,showing the maturation of the microvilli of the enterocyte.On 30 dph,the liver and pancreas developed progressively and occupied most part of the abdominal cavity as the fish grew,demonstrating maturation of the digestive system.4.Variation of digestive enzyme activities in S.Curriculus during the early developmental stagesWith the method of enzymatic assay,amylase,lipase,alkaline phosphatase,and pepsin activities were detected during 0-30 dph.The activity of digestive enzyme activity in S.Curriculus showed different trends between different types of enzymes.Amylase activity(AMS)and Lipase activity(LPS)were detected as early as hatching,and AMS peaked on 15 dph,and then decreased until 30 dph.LPS decreased during the first two days with the exhausting of yolk sac,and then fluctuated,remaining almost constant until 30 dph.Trypsin activity(TRY)was not detected until 8 dph,and reached the peak on 20 dph.Pepsin activity was low during the larval stage.It remained stable during the first 8 days after hatching,and then increased to reach the first peak on 10 dph.As an agastric fish,the activity of pepsin was still detected after hatching,and fluctuated during the ontogenetic development which could be related to acidic and neutral glycoproteins producing by the digestive tract.Alkaline phosphatase activity reached to the maximum on 15 dph,consistent with enterocyte maturation and its absorptive function,which marked the maturation of the digestive system.