| Water transparency is an important index of water quality, which has a greatinfluence on the growth of the organism in water and is mainly influenced by thesuspended substance in water such as algae of the plankton, debris anddissolvedorganic matter etc. Bivalve shellfish can deposit the suspended matter that is difficultto precipitate by depositing dung or false waste forms in its filter feeding. The filterfeeding of the bivalve shellfish can significantly improve water quality, increasing thetransparency of water. This study used three experimental groups: cultured Meretrixlyrata only, cultured Gomphina aequilatera only and cultured Meretrix lyrata andGomphina aequilatera mix in the same biomass. The three groups treatmented withdifferent baits, the same bait but different concentration, different stocking densityand mixed bait feeding, in orde to regularly determine the change of transparency,turbidity, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen content of the water.Andscreenen out the optimal culture conditions of the bivalve shellfish to improve itswater transparency. The major research contents and results were as follows:1. The effect of Meretrix lyrata feeding singlely on water transparency(1)Determining the transparency of the seawater after feeding flour, oceanic redyeast and Chlorella, we knew the three experimental groups had significantdifferences (P<0.05) in the transparency when cultured for20days. In this threegroups, Chlorella group had the highest transparency, yeast group secondly, and flourwas the lowest. The determination of water turbidity showed that Chlorella group hadsignificant difference (P<0.05) with the other two groups when cultured for20days,and after26days, flour group had significant difference (P<0.05) with yeast group inwhich Chlorella group had the lowest turbidity, then yeast group and flour was thehighest. After measuring the changed condition of the nitrate nitrogen, nitrite nitrogen,and ammonia, it showed that the average of Chlorella group inorganic nitrogennutrient was the lowest. According to the above conclusions the Meretrix lyratafilter~feeding to chlorella was better.(2)Analyzing the water transparency and the turbidity. After feeding differentconcentrations of Chlorella (low concentration of4×104cell/mL,middle concentrationof8×104cell/mL, high concentration of12×104cell/mL), it showed that the high concentration group had significant difference (P<0.05) with the other two groups,butthe middle concentration group and the low concentration group was not significant.So it had a good filtering absorption when feed Meretrix lyrata with the middleconcentration and the low concentration. After measuring the changed condition ofthe nitrate nitrogen, nitrite nitrogen and ammonia,it showed that the average of theinorganic nitrogen nutrient in the middle concentration group was the lowest.Accordingly, Meretrix lyrata could maintain better transparency and more effectiveindirectly remove inorganic nitrogen in water when the concentrations of Chlorellawas8×104cell/mL.(3)After measuring the water transparency and the turbidity when used the fixedamount of Chlorella to feed the different weight（300g,600g,900g）of the Meretrixlyrata, it showed that the three weight groups not significant difference(P>0.05), Thechanged trend of the turbidity value was consistent with the transparency. Aftermeasuring the changed condition of the nitrate nitrogen, nitrite nitrogen and ammonia,it showed that the average of the inorganic nitrogen nutrient of middle concentrationgroup was the lowest. The results showed Meretrix lyrata can maintain bettertransparency and had low levels of inorganic nutrients when the density was600g.2. The effect of Gomphina aequilatera feeding singlely on water transparency(1)Determining the seawater transparency by feeding flour with flour, oceanicred yeast and Chlorella, it showed that there was no significant difference among thethree experimental groups (P>0.05). the changed trend of th turbidity value andtransparency was consistent. And three groups had no significant difference. Afteranalyzing the turbidity Chlorella group was minimum with NTU0.06, Then yeastgroup and flour group was highest. Thus selected Chlorella as the optional feed.(2)After determining the water transparency of the different feed concentrationsof Chlorella (low concentration of4×104cell/mL, middle concentration of8×104cell/mL, high concentration of12×104cell/mL), it showed that no significantdifference among the three experimental groups (P>0.05). By the end of the26day,the low concentration group had the highest transparency (value was51.13cm),then the middle concentration group and the high oncentration group had the lowesttransparency value.In the changed of the turbiditythe high oncentration group wasmaximum (P>0.05), and the difference was not obvious between the middle and lowconcentration. The average of the middle concentration group inorganic nitrogennutrient was the lowest, So in contains abundance (8×104cell/mL) of chlorella in water, Gomphina aequilatera could better indirectly remove inorganic nitrogennutrient in water.(3)By feeding Gomphina aequilatera of different biomass (300g,600g,900g)with fixed amount of Chlorella, there were significant differences of transparencyamong the three experimental groups (P<0.05), which the biomass (600g) washighest, but water turbidity had no significant difference (P>0.05). After measuringthe changed condition of the nitrate nitrogen, nitrite nitrogen and ammonia, it showedthat the average of the inorganic nitrogen nutrient inthe middle concentrationgroupwas the lowest. Accordingly, middle density group of Gomphina aequilaterawas better than the other groups to keep the water transparency.(4)Feeding different size (small, middle and big) of Gomphina aequilatera withfixed amount of Chlorella,(biomass of each group was600g), it showed nosignificant difference in transparency among the three experimental groups (P>0.05).but water turbidity had significant difference (P<0.05), and middle size group waslowst in the three groups. After measuring the changed condition of the nitratenitrogen, nitrite nitrogen and ammonia, it showed that the average of inorganicnitrogen nutrient of the middle size group was the lowest. Accordingly, the middlesize group of Gomphina aequilatera was better to keep the seawater transparency.3. The effect of M.lyrata and G.aequilatera with the same biomass feeding on watertransparency(1) Determining the seawater transparency by feeding flour, oceanic red yeastand Chlorella, it showed the transparency was not significant among the threeexperimental groups (P<0.05), in which the value of Chlorella group was maximum,was46.91cm, followed the yeast group, and flour group was the lowest, The changedtrend of the turbidity and transparency value was consistent with transparency amongthem. According to the results, the Chlorella group was the best fed diets to keep theseawater transparency.(2) The transparency of seawater was not significant difference when feddifferent concentrations of Chlorella to polyculture group (low concentration of4×104cell/mL, the medium concentration of8×104cell/mL, a high concentration of12×104cell/mL)(P>0.05), but turbidity value had higher significant differences (P<0.05), inthat the medium and low concentration were the lowest. After measuring the changedcondition of the nitrate nitrogen, nitrite nitrogen and ammonia,it showed that theaverage ofinorganic nitrogen nutrient of the middle concentration group was the lowest. The results suggest that feeding the medium concentration Chlorella（8×104cell/mL）was best for polyculture group.(3) By feeding the mixed baits (Chlorella and marine red yeast) to M.lyrata.G.aequilatera and polyculture group showed the transparency was significantdifference (P<0.05), in which the transparency of G.aequilatera was highest, whith45.01cm, polyculture group secondly and M.lyrata was minimum. And the changetrend of the turbidity and transparency value was consistent, but the average ofinorganic nitrogen nutrient of the polyculture group was the lowest. Thus, the effect offilter feeders was better when culture of single Gomphina aequilatera, and the effectwas best that shellfish indirectly remove inorganic nitrogen of water under polyculturenutrient efficiency. |
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