Screening And Research Qualified Forage As Fish Fodder To Grass Carp In Mountainous Area Of South China

1,The results showed that,the feed-taking rates of cool-season forages,Lolium multiflorum Lam and Dactylis glomcrata L.during vegetative period by grass carp were 74.03%and 70.09% respectively which obviously higher than that of Medicago sativa L.amount for 45.32%.It means the better palatability of Lolium multiflorum Lam and Dactylis glomcrata L.than Medicago sativa L.Results also revealed that the palatability of forages during vegetative period was clearly better than that during heading or flower-emerging periods.The feed-taking rates of warm-season forages,Ipomoea batatas Poior leaves and Pennisetum americanum×P.purpureum CV.23A×N51 during vegetative period by grass carp were the highest,amount for 61.98%and 56.15% respectively,which were much higher than that of Setaria anceps Stapf cv.Kazungula amount for 33.76%.Others were located between these values.2,The annual hay weight of Pennisetum americanum×P.purpureum CV.23A×N51 which grows in mountainous red soil area of south China reached 26127.95kg/hm~2,that of Vigna sinensis sari Var reached 19339.70kg/hm~2.Both of these two forages possess the merits of long green-fodder providing period,rapid recovering capacity after cutting,may serve as major cropping varieties for pisciculture in the mountain areas.3,The suitable harvesting period of Pennisetum americanum×P.purpureum for fish use is 28d.4,In a 60d trail,the daily weight gain per piece fish in the group feeding compound feed and supplementing Pennisetum americanum×P.purpureum was 15.61±0.14 g,that in the group supplementing Vigna sinensis sari Var was 15.03±0.34 g,both of them were higher than the ck (feeding compound feed only,9.66±0.26g).Variance analysis showed the very significant difference(P＜0.01) between treatments and ck.This fact demonstrated that feeding Pennisetum americanum×P.purpureum and Vigna sinensis sari Var may significantly improve the weight gain of grass carp.5,The experiment indicates that grass carp were fed the feed at 1:1 ratio of compound feed and Pennisetum americanum×P.purpureum CV.23A×N51,the multiple indexes of herbivore-fish,such as plumpness,the viscera rate,intestines-fat rate,body rate and intestine/body length rate,all shown the remarkable differences(p＜0.05)between treatments and CK(fed compound feed only).Especially,intestines-fat rate of the latter(fed compound feed only),which is 3.14 times of the former that is 1.42%,is 4.46%,the content of fat in the latter's fish(fed compound feed only),which is 4.74 times of the former that is 2.15%,is 10.20%(p＜0.05).6,The relative content of PUFA in the fish fed grass was 40.18±1.36%and was 1.86 times of the fish fed full compound feed(21.64±0.98%).The relative content of n-3 PUFA in the fish fed grass was 14.72±1.27%and was 6.06 times of the fish fed full compound feed(2.43±0.49%).Especially,The relative content of 18:3n—3 in the fish fed grass was 10.27±1.21%and was 10.17 times of the fish fed full compound feed(1.01±0.02%).The fatty acid components in the leaves of Pennisetum americanum×P.purpureum CV.23A×N51 and compound feed were also compared.It was found that,the content of 18:3n—3 in the leaves of Pennisetum americanum×P.purpureum CV.23A×N51 was as high as 66.23±0.16%and that in compound feed was only 4.34±0.03%.None of EPA and DHA were detected in both Pennisetum americanum×P.purpureum CV.23A×N51 and compound feed.Grass carps converted the abundant 18:3n—3 in grass to EPA or DHA and thus increased the relative content of n-3PUFA in the fish fed grass,Feeding grass increased the fish growth and development,enhanced its disease-resistance and improved fish muscle quality.