Study On The Effect Of Different Culture Environment On The Ecophysiology Of Grass Carp (Ctenopharyngodon Idellus) Using Photosynthetic Pigments And Fatty Acids As Biochemical Markers

To assess the effects of different cultural modules, including the monoculture ofgrass carp (Ctenopharyngodon idellus), monoculture of silver carp(Hypophthalmichthys molitrix) and the polyculture of grass carp and silver carp, onthe community structure of phytoplankton, the community structures ofphytoplankton in the culture waters were analyzed by means of HPLC analysis ofdiagnostic pigment and fatty acid profiles. In addition, the effect of differenttemperatures on the fatty acid composition of grass carp muscle was examined.Finally, to elucidate the nutrient metabolism of grass carp, the C, N, P budgets ofgrass carp in different temperature were examined. The main results are listed asfollows:1． Effect of grass carp-silver carp polyculture on the community structure ofphytoplankton using diagnostic pigment analysisTo assess the effect of the filter-feeding silver carp on the community structure ofphytoplankton in the grass carp-silver carp polyculture module,3cultural modulesincluding the monoculture of grass carp (G group) and silver carp (S group), andpolyculture containing grass and silver carps (GS group) were set up in ShandongFreshwater Fisheries Institute from August to October2011. Samples ofphytoplankton were collected and the community structure of the phytoplankton was determined by means of HPLC analysis of diagnostic pigment and microscopicenumeration. The results showed that phytoplankton community structure wassignificantly different between the three farming waters. Phytoplankton biomass of Sgroup was significantly lower than those of G and GS group, and the dominantspecies in the three farming waters appeared significant difference. In S group, thedominant species included Scenedesmaceae, Closterium Nitzsch and Synedra,whilefor G group, the phytoplankton composition was dominated by Achnanthes,Phormidium, Aphamnizomenon and Synedra. In GS group, Scenedesmaceae was themost dominant species.The highest content of photosynthetic pigments waschlorophyll a, followed by chlorophyllide a. The concentrations of some charactisticpigments were significantly correlated to the phytoplankton biomass, such as thecorrelations between fucoxanthin and Bacillariophyta, Lutein and Chlorophyta,zeaxanthin and Cyanophyta (P<0.01). The pigment concentrations and inorganicnitrogen, labile phosphorus were not correlated significantly in S or GSgroup(P>0.05) while some pigment concentrations and ammonium nitrogen, nitritenitrogen showed significant correlations in G group(P<0.05).2. Effect of grass carp-silver carp polyculture on the community structure ofphytoplankton using fatty acid analysisTo assess the effect of the filter-feeding silver carp on the community structure ofphytoplankton in the grass carp-silver carp polyculture module,3cultural modulesincluding the monoculture of grass carp (G group) and silver carp (S group), andpolyculture containing grass and silver carps (GS group) were set up. Fatty aicdcompostion of the phytoplankton which was collected from the3groups wereanalyzed. The results showed that the phytoplankton community structure and contentof fatty acids were both significantly different between the farming waters.Phytoplankton biomass of S group was significantly lower than those of G and GSgroup, and the dominant species showed significant difference between the farmingwaters. In S group, the dominant species included Chlorophyta and Bacillariophyta, while for G group, the phytoplankton composition was dominated by Cyanophyta. InGS group, Chlorophyta sp. was the most dominant species. C16:0was the mostprincipal fatty acid in terms of concentration, and the content of C16:0andCyanophyta sp. biomass were correlated significantly（r=0.979,P<0.01）. The highestconcentration of fatty acids was saturated fatty acid, and for the total fatty acids,Ggroup>GS group>S group.3. Effects of different temperatures on the fatty acid composition of grass carpmuscleGrass carp was cultured in4different temperatures including15℃,18℃,24℃and30℃. The comparisons of neutral lipid fatty acids and phospholipid fatty acidsextracted from the muscle of grass carp were analyzed and compared between4different temperatures. The results showed that a total of18fatty acids inphospholipids and neutral lipids were determined with significant difference in theproportional compositions of the fatty acids. Fatty acid composition of the neutrallipids did not change with regular trend following the increasing temperature. For thephospholipid, the length of fatty acid chains were more elongated compared with thatof the neutral lipids and the concentrations of unsaturated fatty acid (UFA) increasedwith decreasing temperature.4. Effects of temperature on the C, N, P nutrient budgets of grass carpThe present experiment simulated the temperature fluctuation during theculture period of grass carp Hypophthalmichys molitrix so as to examine the effects ofthe changes in temperature on the nutrient budgets of C, N and P. Grass carp werecultured in the temperatures of15℃、18℃、24℃and30℃and the process of C, Nand P budgets were examined. The results showed that C, N, P nutrient budgets ofgrass carp were significantly different between the4temperature groups(P<0.05).With increasing temperatures, the oxygen consumption rate and absorption rates of C, N and P of grass carp increased while nitrogen excretion rate,phosphorusexcretion rate, feed uptake rate and fecal egestion rate increased at the beginning ofthe experiment and then decreased. As a result, the scope for growth (SGF) of C, Nand P of grass carp increased at the beginning of the experiment then decreased.