AlMH HUQIMG C U A IVIAT D O , L O A I T H U C AIM DEIM SIIMH TRUQIMG V A T Y LE SOIMG C U A LUOIM DOIMG
n/lanapterus albus (Zuiei/v, 1 7 9 3 ) IMUOI TROIMG BE
Nguyin Htiu Kh^nh, H 6 TTii Bich NgSn^
T6MTAT
Sinh truong va ty le song cua luon dong (Monopterus albus) dugc xac dinh khi nuoi trong be ni long trong thai gian 6 thang a bon mat dp khac nhau (0,5,1, 2 va 3 kg/m^) va a 3 loai thuc an (tbifc an tuoi, che bi6n va thirc an cong ngbiep). Mat do nuoi co anh huong den sinh trucmg va ty le song cua luon. Toe dp tang trucmg tuyet doi (DWG) cua lucm dat 1,00 g/ngay a mat dp 0,5 kg/m^ va 0,99 g/ngay a mat do 1 kg/m^ cao bcm CO y nghia so vol thong so nay a hai nghiem thiic con Iai (2 va 3 kg/m^) voi gia tri lan luot la 0,86 va 0,68 g/ngay {P < 0,05). Ty le song trung binh ciia luon dat 92,1%, 91,5%, 73,1% va 73,5% tuong ling a cac mat dp 0,5,1, 2 va 3 kg/ml Luon nuoi a nghiem thiic sir dung thiic an cong nghiep co toe dp tang trudng thap ban so voi a nghiem thirc sir dung thiic an che bien va thirc an tuoi voi gia tri toe dp tang trucmg Ian lupt la 0,78,1,06 va 1,08 g/ngay {P < 0,05). Tuy nhien, khong c6 su khac biet ve ty le song giiia cac nghiem thiic su dung thiic an khac nhau. Ket qua ngbien ciiu cbo thay nuoi luon trong be ni long o mat dp < 1 kg/m^ va str dung thiic an tuoi hay che bien la phu hpp.
Ttr kh6a: Luon ddng, sinh trudng, mat do, thtic dn.
LMffDAU
Luon dong Monopterus albus (Zuiew, 1793) phan b6 tu nhien o' viing nhiet dai, can nhiet doi chau A, tir An Dp den Trung Qu6c, Nhat Ban, Malaysia, Indonesia, Banglades (Froese & Pauly, 2008; Guan &
CS., 1996), Thai Lan (Thongrod & CS., 2004) va Viet Nam. Luon la loai dpng vat dii, an thit, boat dpng ve dem. Thitc an chii yeu la ca, cua va tep (Ly Van Khanh & CS., 2008). Luon co pho thiic an rpng bao gom: Giun, 6c, tom, tep, ca, au trung chuon chuon, nong npc... (IIRR, 2001). Luon s6ng trong moi truong CO pH trung tinh, nhiet dp thich hpp 22-30"C, luon co the s6ng trong dieu kien moi truong co ham lupng oxy hoa tan thap. Toan b6 chu ky s6ng ciia luon diin ra a viing nuac ngpt, moi truong s6ng kha da dang nhu dam lay, rupng lua, song, su6i, kenh, muong, ao, ho tu nhien hay nhan tao... (Frosese & Pauly, 2008).
Thit luon giau dinh duong va la vi thu6c quy trong y hpc co truyen (Nguyin Van Thong 2008). Do nhu cau tieu thu Ion, gia ban cao va nguon loi luon khai thac tu nhien ngay cang can kiet nen nghe nuoi thuang pham luon dong dang dup'c phat trien. Nuoi luon sau nha duac cho la mot boat dpng kinh doanh CO chi phi thap, d l thuc hien va mang Iai nhieu Ipi nhuan (IIRR, 2001; Lu & CS., 2005). Hien nay, luon dupc nuoi a nhieu qu6c gia nhu Trung Qu6c,
Vien Nghien ciru Nuoi trong Thiiy san 3
Philippines, Thai Lan, Indonexia, Viet Nam ... 6 Viet Nam, nghe nuoi luon phat trien 6' nhieu dia phuang til An Giang, Can Tha, Hau Giang, Dong Thap den Dong Nai, Nghe An... Tuy nhien, boat dpng nuoi thuong pham luon dong o' Viet Nam la tu phat, ky thuat nuoi chua hoan thien nen nguoi nuoi d l rui ro.
Cac nghien cuu ve nuoi luon ban che, cac tai lieu nghien ciru da dup'c cong bo rat it hoac kho tiep can.
Do do, viec nghien cuu anh huong cua mat dp nuoi va loai thitc an den luon dong nuoi la can thiet de co khuyen cao phii hpp cho nguoi nuoi.
II. VAT UEU VA PHUDNG PHAP NGHIEN CUU
1. Dia di^m fhuc nghiem vk luon gi6ng
Thi nghiem dugc tien hanh tai khu nuoi trong thiiy san Lac Dia, huyen Ba Tri, tinh Ben Tre.
Luon dong (Monopterus albus) co ngu6n g6c ttr tu nhien, kich ca trung binh 40 con/kg. Luon dupc mua a Ba Tri, Ben Tre tir nguoi thu gom luon khai thac tu nhien bang cac nghe don, tnim.
2. B l nuoi vk c h u l n bi b l
Be thi nghiem Iam bang bat khong tham nuo'c, CO kich thuac 1,6 x 2,5 x 0,8 m. Be duac co dinh hinh dang nho' cac cpc g6, tre, tram, tram bau va cac nep tam vong, tre. Day be co 15 thoat nuac hinh tron, duac Iam bang 6ng nhua PVC, duong kinh 8-10 cm.
Be duac chuan bi theo huong din cua IIRR (2001): 'A
KHOA HOC CONG NGHE
be de tr6ng; phan be con Iai duoi day de mot lap dat set day khoang 10 cm, ke do xep 1 lap ram 10 cm, 1 lop than chu6i day 10 cm. Tiep den la lap phan bo kho, cung day 10 cm, va tren cung la lap dat rupng day 10-20 cm. I i y nuac vao be, ngam xa be trong vong 1 thang den khi het vang bpt.
Sau khi tha luon vao, giii muc nuac trong be 40- 50 cm va miic nuoc nay thap hon mo dat lam ch6 tni an cho luon tir 10-20 cm. Trong rau mu6ng, co nuac len mo dat, de chung phat trien che kin toan bp mo dat, giiip che mat cho be.
3. Cke nghifem thiic thi nghiem a. Thi nghiem vi mat do nudi
Thi nghiem gom co 4 nghiem thuc la 0,5, 1, 2 va 3 kg/m^, kich ca luon giong 40 con/kg. M6i nghiem tbiic dugc lap Iai 3 Ian. Don vi thi nghiem la be bat 4 m l Thi nghiem keo dai trong 173 ngay (03/02/2008- 25/07/2008). Thiic an cho luon la thuc an che bien, cho an 1 lan/ngay vao bu6i chilu t6i.
b. Thi nghiem ve loai thuc dn
Thi nghiem thiic an gom 3 nghiem thuc, m6i nghiem thiic dugc lap Iai 3 Ian. Don vi thi nghiem la be bat 4 m^. Mat dp tha 1 kg/m^. Thoi gian thi nghiem keo dai 151 ngay (tu 25/02/2008- 25/07/2008), khong ke thoi gian tap cho luon quen dan vol thiic an cong nghiep trong 22 ngay (tii 03/02/2008-25/02/2008). Thanh phan dinh duong cua cac loai thuc an dugc ghi lai trong bang 1.
Bang 1. TTiinh phin dinh duong (% theo vkt chit kho) cua thiic an chi biln, ihiic an cong nghi$p vk thiic an tuoi
Chi tieu Protein Lipit Xo toi da P toi thieu Do am
Thirc an che bien
36 4,1 4,8 - 35-40
Thiic an cong ngbiep
30 5 6 1 11 (toi da)
Thiic an tuoi (*) 52,8
1,8 1,4 20,9 (*): Theo Lgi Vdn Hiing (2004)
Thiic an tuai la thit 6c buau vang. Thiic an che bien bao gom thit 6c huou vang ket hpp voi thiic an vien Cargill 30% dam diing cho ca (ty le 2:1) dugc xay nhuyin, trpn voi chat ket dinh (bpt gon) truac khi cho vao sang an. Tat ca cac nghiem thuc thuc an deu dugc bo sung vitamin C, men tieu hoa de tang siic de khang cho luon va giiip tieu hoa thiic an t6t hon. Lieu
lupng sir dung theo huong dan cua nha san xuat (5 g vitamin C/kg thiic an va 1-2 g men tieu hoa/kg thiic an).
Thiic an du thira dugc loai bo khoi be nuoi vao luc sang som de tranh lam 6 nhilm moi truong nuac.
Cho luon an 1 lan/ngay vao luc chieu t6i. Khau phan thuc an 5-8% kh6i lupng than, co su dieu chinh thirc an theo nhu cau sir dung.
4. Phuong phdp ihu mSu vk cke chi ti^u so s4nh Nhiet dp va pH dugc xac dinh 2 lan/ngay vao bu6i sang va chieu bang nhiet ke va may do cam tay.
Dinh ky 2 lan/thang thu mlu phan tich chi tieu nitrit, amonia va HjS theo Boyd (1998) va APHA (1999).
Khi bat dau va Iiic ket thiic thi nghiem thu mau ngiu nhien, m5i mlu thu it nhat 36 ca the, can, do kh6i lugng ciia timg ca the. Trong thoi gian thi nghiem, dinh ky thu mau moi thang mpt lan, can toan bp so luon trong mau thu dugc de tinh kh6i lupng than trung binh.
Ty le s6ng dugc tinh dua vao s6 luon liic bat dau tha va ket thiic thi nghiem.
He s6 tieu t6n thirc an dugc tinh dua tren s6 lugng thiic an da sir dung va kh6i lupng luon tang len.
S6 lieu thu thap dugc xir ly bang phuong phap phan tich phuong sai mpt yeu t6 (one-'way ANOVA) de danh gia su sai khac giQa cac nghiem thirc 6' muc y nghia a = 0,05. So sanh su khac nhau cua cac nghiem thiic bang Turkey HSD test trong phan m i m Statistical.
III. KET QUA NGHIEN CUU
1. Anh huong ciia mM do nuoi din sinh tnrong vd ty l l song cua luon
a. Chdt luang nu&c trong cdc be thi nghiem Cac thong s6 moi truong nuac gan nhu 6n dinh su6t giai doan thi nghiem va khong co su khac biet CO y nghia giCra cac nghiem thiic (P > 0,05). Nhin chung, cac yeu t6 moi truong cua be nuoi deu nam trong gioi han thich hpp: nhiet dp 28-31"C, pH 6,8- 7,2, NO2 0,01-0,05 mg/L, NH3 0,01-0,04 mg/L va H2S 0,03-0,08 mg/L. Cac thong s6 nay nam trong giai ban phu hpp ve tieu chuan chat lupng nuoc cho nuoi trong thuy san dugc mo ta boi Boyd (1998).
b. Ket qud sinh tru&ng ciia luan
Ket qua nghien ctm cho thay, mat dp nuoi co anh huong den sinh truong cua luon dong nuoi trong be ni long. Duong cong tang truong cua luon a 2 nghiem thiic 0,5 kg/m^ va 1 kg/m^ gan triing khit len nhau (Hinh 1). Trong ba thang nuoi dau khong co su khac biet giiia cac nghiem thiic thi nghiem. Ttr thang nuoi thu 3 tro di, tang truong ciia luon a cac nghiem thirc bat dau c6 su khac nhau. Su tang truong 6' nghiem thirc mat dp 0,5 kg/m^ va 1 kg/m^ vugt troi so vai hai nghiem thiic mat dp 2 kg/m^ va 3 kg/m^ (P < 0,05).
T6C dp tang truong tuyet d6i (DWG) cua luon la 1,00 g/ngay a mat dp 0,5 kg/m^ va 0,99 g/ngay o' mat dp 1 kg/m^ cao hon c6 y nghia so voi gia tri nay a 2 nghiem thirc con Iai 0,86 va 0,68 g/ngay tuong img a mat dp 2 va 3 kg/m^ (P < 0,05). T6c dp tang truong trung binh ve kh6i lugng cua luon SGR (%/ngay) giiia 3 nghiem thirc mat do 0,5 kg/m^ 1 kg/m^ va 2 kg/m^ khong co su khac biet co y nghia
(P > 0,05). O nhom nay, gia tri SGR dao dpng tir 1,12 (%/ngay-nghiem thiic 2 kg/m^) den 1,19 (%/ngay-
nghiem thirc 0,5 kg/m^) cao hon so voi nghiem thirc 3 kg/ml Ket qua nay tuong tu voi ket qua nghien ciiu ciia Zhou & Li (2004) khi thir nghiem nuoi luon bang thuc an tuai (giun dat, nong npc, gioi) co toe dp tang tilling (TDTT) 0,33-1,2%/ngay (Bang 2).
225 200 _ 175
Bat dau
Hinh 1. Tang truong khii lugng ciia luon trong quk trinh nuoi a eke mat do khde nhau
Bing 2. Toe do tang truong vkty\& s6ng cua luon nu6i a eke mzit do khkc nhau
Thong so Khoi lupng than khi tha (g) Khoi lupng than khi thu hoach (g) TDTT tuyet doi-DWG (g/ngay) TDTT tuOTig doi-SGR (%/ngay) Ty le song (%)
He so tieu ton tbiic an Nang suait (kg/mVvu)
Mat dp tha (kg/m') 0,5
25,1 ± 4,0"
197,5 ± 64,r 1,00 ±0,03=
1,19 ±0,01"
92,1 ± 2,6-'' 5,1 ±0,8=
3,8±0,r
1 25,3 ± 4,0'=
195,8 ± 6 7 , r 0,99 ± 0,06"
1,18 ±0,04'=
91,5 ± 5,3''' 5,2±0,2''' 7,9 ±0,9"
2 25,1 ± 3,6'"
172,8 ± 50,6'' 0,86 ± 0,04'' 1,12 ± 0,03-=
73,1 ± 8,8'' 7,2 ±0,6'' 9,9 ± i , r
3 25,1 ±3,9"
143,2 ± 40,9' 0,68 ± 0,05^
1,01 ± 0,03"
73,5x7,1'' 6,2 ± 0,6''''' 11,1 ±0,5'
Luon thuong pham dugc phan Iam 3 loai theo yeu cau tieu thu cua thi truong: loai 1 (>200 g/con), loai 2 (100-200 g/con), loai 3 (<100g/con). Ket qua phan loai luon sau thu hoach cho thay co su khac biet ve ty le cac loai luon giiia cac nghiem thirc thi nghiem. Ty le luon loai 1 giam trong khi luon loai 2 va 3 tang 6' cac mat d6 tha cao hon (Hinh 2).
Ghi chii: Gid tri trinh bdy la gid tri trung binh O do lech chudn. Trong ciing mgt hdng, cdc chU sd khde nhau kem theo minh hoa cho stt sai khde co y nghia thdng ke (P<0,05).
Ty le s6ng ciia luon a cac nghiem thiic thi nghiem phan thanh 2 nhom, nhom mat dp 0,5 - 1 kg/m^ va nhom mat dp 2 - 3 kg/m^ va co su sai khac CO y nghia th6ng ke (P < 0,05). Mat dp nuoi co anh huong den ty le s6ng ciia luon, khi tang mat dp den miic khong thich hpp se Iam giam ty le song ciia luon.
100
30-
SO
y
1
a
h
I
a> louga ^jooa
i.5 kgj'm" 1 ]-:.^'m'^
r./
M^iuciii thuc
Hinh 2. Ty 16 (%) cke nh6m khoi lugng luon khi ihu hoach.
Trong ciing nhom khdi lugng, cdc chit sd khac nhau kem theo minh hoa cho sit sai khde co y nghia (P<0,05).
KHOA HOC CONG NGHE
2. Anh huong cua loai thiic an din sinh truong va ty l l song cua luon
a. Dieu kien mdi tru&ng cua cdc be thi nghiem Cac ylu t6 moi truong deu nam trong khoang gioi ban thich hgp ve chat lupng nuac cho nuoi thuy san (Boyd 1998). Gia bi NH3, NO2, HjS a nghiem thirc thiic an cong nghiep thap hon co y nghia so voi nghiem thirc che bien cho thay sir dung thirc an cong nghiep se it gay 6 nhiem moi tni'ong hon (P < 0,05). Do cac be nuoi dugc thay nuoc thuong xuyen nen anh huong cua loai thiic an den chat lugng nuoc chua the hien ro net.
Dieu chac chan la sir dung thirc an che bien se Iam chat lugng nuoc bi 6 nhiem nhieu ban (Bang 3).
Bang 3. Mot so ylu to moi trudng nuoc or cke nghifem thiic sii dung thiic an k h ^ nhau
Thong so Nhiet dp (°C) pH
NH, (mg/L) NO, (mg/L) H,S (mg/L)
Nghiem thirc Thiic an tuoi
30,0 ±1,9 7,1 ±0,1 0,03 ± 0,005'"
0,04 ± 0,004="
0,09 ± 0,004=
Tbiic an che bien 29,9 ± 2,0
7,2 ±0,1 0,03 ± 0,004=
0,05 ± 0,005=
0,10 ±0,017=
Thiic an cong nghiep 30,0 ±1,9
7,1 ±0,1 0,02 ± 0,004"
0,03 ± 0,005"
0,06 ±0,011"
Ghi chii: Gid tri trinh bdy Id gid tri trung binh ± do lech chudn. Trong ciing mot hdng, cdc- chu sd khde nhau kem theo minh hga cho susai
khde CO y nghia thdng ke (P < 0,05).
b. Ket qud sinh tru&ng cua luan
Tang truong vl khoi luong luon khong co su khac biet co y nghia giiia nghiem thirc thuc an tuoi va nghiem thiic thirc an che bien, gia trj SGR dat 1,11%-1,12%/ngay cao hon han so voi 6 nghiem thiic thii'c an cong nghiep 0,94%/ngay (P < 0,05). Mac dii khoi lugng trung binh cua luon 6' nghiem thirc thirc an cong nghiep thap hon dang ke so voi a 2 nghiem thii'c con lai (155,6 g/con so vai 200,4 g/con va 195,8 g/con) nhung viec luon sir dung dugc thirc an cong nghiep la mpt tin hieu kha quan de giai quyit van de thirc an cho n g h l nuoi luon cong nghiep sau nay (Bang 4).
Ty le s6ng trung binh cua luon a nghiem thiic thiic an tuoi, che bien va thirc an cong nghiep Ian lugt
la 88,5± 5,2%, 91,5 ± 5,3%, 89,2 ± 10,4%. Khong CO su khac biet co y nghia dugc tim thay giQa cac nghiem thuc khac nhau (P > 0,05).
He s6 tieu ton thirc an a nghiem thirc sir dung thiic an cong nghiep thap hon dang ke so voi 2 nghiem thirc con lai mac dii thanh phan dinh duang ciia thirc an cong nghiep khong cao hon thirc an tuoi va che bien la vi thanh phan dinh duong cua thiic an dugc tinh theo vat chat kho, trong khi lugng thuc an tieu ton dugc tinh theo kh6i lugng tuai.
Bang 4. Sinh truang ciia luan nuoi or eke nghiSm thiic thiic an khic nhau Thong so
Khoi lupng khi tha (g) Khoi luong khi thu hoach (g) TDST tuyet doi- DWG (g/day) TDST tuong doi SGR (%/day) Ty le song (%)
He so tieu ton thiic an Nang suat (kg/m'/vu)
Nghiem tbiic Thiic an tuoi
37,5 ±5,1=
200,4 ± 62,4=
1,08 ± 0,08=
1,11 ±0,04=
88,5± 5,2%
8,4 ± 0,6=
6,5 ± 0,3="
TA che bien 37,1 ± 5,7=
195,8 ± 6 7 , r 1,06 ± 0,07=
1,12 ± 0,02=
91,5 ±5,3%
5,2 ± 0,2"
7,9 ± 0,9=
TA cong ngbiep 37,4 ± 4,1=
155,6 ± 50,5"
0,78 ± 0,04"
0,94 ± 0,03"
89,2 ± 10,4%
3,7 ± 1,3^
5,6 ± 0,5"
Ghi chii: Gid tri trinh bdy Id gid tri trung binh O do lech chudn. Trong cung mot hdng, cdc chit sd khde nhau kem theo minh hga cho su sai khde cd y nghia thong ke (P<0,05).
Ty le luon loai 1 cao nhat 6' nghiem thiic thirc an che bien (69,5%), ke den la 6' nghiem thirc thiic an tuoi (62,1%) va thap nhat o' nghiem thirc thiic an cong nghiep (36,2%). Khac biet vl ty le cac loai luon 6' nghiem thirc thirc an cong nghiep (loai 1 thap nhat, loai 3 cao nhat) voi nghiem thirc thirc an tuoi va thirc an che bien la su sai khac co y nghia (P <
0,05) (Hinh 3).
Tir k i t qua tren cho thay sir dung thirc an che bien de Iam thirc an cho luon dong tuong tu nhu sir dung thirc an tuoi. Viec sir dung thiic an che bien co y nghia thuc tiin khi ma nghe nuoi phat trien thi nguon thiic an tuoi la 6c buau vang se khong the cung irng dii cho nhu cau.
100 90 80 70 60 50 40 30 20 10 0
•
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+
b
i^' 2:k^....
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' • / ' ?^-H
DLoai 1 n Loai 2 D Loai 3
TA Uroi TA che bien TA cong nghiep
Nghiem thirc
Hmh 3. T^ 11 (%) c4c nhom khoi lugng luon khi thu hoach.
Trong ciing nhom kich ca, cdc chu sd khde nhau kem theo minh hoa cho su sai khde co y nghia (P < 0,05).
3. Hiiu qua kinh t l
Ty suat lgi nhuan a nghiem thiic 1 kg/m^ cao nhat voi gia tri dat 34,3% cao hon 4 Ian so voi nghiem thiic 2 kg/m^ (8,4%), 6 Ian d6i voi nghiem thiic 3 kg/m^ (5,6%) va hon 22 Ian d6i vol nghiem thiic 0,5 kg/m^ (1,5%). Nuoi luon a mat do 1 kg/m^ mang Iai hieu qua kinh te cao nhat voi chi phi san xuat trung binh khoang 531.000 dong/m^ va dat Igi nhuan trung binh 184.000 d o n g / m l
Ty suat lgi nhuan a nghiem thiic thiic an tuoi cao nhat dat gan 40%, ke den thiic an che bien la 34,3% va thap nhat a nghiem thiic thiic an cong nghiep chi dat 8,8%. Sir dung thirc an cho luon la tbiic an tuoi hay thirc an che bien deu mang Iai hieu qua kinh te nhu nhau va cao ban dang ke so voi sii dung thirc an cong nghiep. Chi phi san xuat trung binh khi su dung thuc an tuoi va che bien Ian lugt la 411.000 d6ng/m^ va 531.000 dong/m^ mang Iai Ipi nhuan trung binh tuong ung la 163.000 dong/m^ va 184.000 d6ng/m^(Hinh4).
3.3 3C 2 5 2 C 1 5 1 0 0 5 OC
r^
IT.
r m . ^
lAtuoi TAchebian TA :6r.g ngh;sp Ng-.iem th'jc
E Chi rhi sir. :^k C roa.nh '.hu C Lo: nh'jar.
EDnh 4. Chi phi san x u ^ doanh thu vA lgi nhu|in orc^
n ^ & n thuc khic nhau.
Theo titng chi tieu, cdc chit so'khde nhau kem theo mink hoa cho susai khac co y nghia (P < 0,05).
4. Thao luan
Kit qua nghien ciiu nuoi luon trong be bat cho thay, mat d6 co anh huong den sinh truong va ty le s6ng cua luon. Tang mat dp se anh huong den sinh truong ciia vat nuoi boi su suy giam ve chat lupng m6i truong s6ng, su canh tranh ve thirc an va khong gian s6ng (Ray & Chien, 1992; Martin & CS., 1998;
Allan & Maguine, 1992). Mat dp nuoi cang cao thi nil ro do dich benh cang Ion va cang thai ra mot lugng Ion chat thai (Pillay 1990). Nuoi luon trong be vol sir cung cap thiic an, khi tang mat dp se tac dpng den chat lugng moi truong be nuoi do lupng thirc an du thira tang. Mac dii vay, ket qua nghien cim da cho thay cac thong s6 moi truong nuac khong co su khac biet giua cac nghiem thirc thi nghiem va deu nam ve trong gioi ban an toan cho sinh truong cua luon.
Dieu nay co the giai thich la do che dp thay nuoc thuong xuyen 2-3 lan/tuan va viec trong cac loai thuc vat thuy sinh trong be phan nao cai thien chat lupng moi truong be nuoi. Lin & Yi (2003) khi nghien ciru kha nang hap thu dinh duong cua thuc vat Ion trong ao nuoi cho thay sen (Nelumbo mucifera) co kha nang loai bo den 300 kg N va 45 kg P/ha/nam. Con luc binh (Eichhornia crassipens) co kha nang bap thu tir 35% den 85% nita, 10% den 90% photpho trong nuoc (Nesis & Jovanovic, 2006).
Viec canh tranh ve thirc an va moi truong song b luon nuoi la rat Ion vi chiing la dpng vat dQ. Ty le cac ca luon luc thu hoach hi anh huong manh boi mat dp tha (he s6 phan tan ve khoi lupng Iiic thu hoach dao dpng 27,9-33,9%). Khi luon dugc tha 6' mat dp cao, su sinh truong cua chiing hi giam va kich ca thu hoach se khong dap img dugc nhu cau cua thi truong sau 6 thang nuoi. Mat do tha cUng co anh huong den ty le s6ng ciia luon, khi tang mat dp den mirc khong thich hgp se Iam giam ty le s6ng cua luon. Trong thi nghiem, ty le s6ng va sinh truong cua luon t6t nhat dat dugc 6' mat dp 0,5 va 1 kg/m^ va mat dp 1 kg/m^
dugc khuyen cao ap dung vi mang Iai nang suat cao hon. Cac nghien ciiu tiep theo nen tap trung hoan thien ky thuat thiet ke be, vat lieu tni an, bien phap quan ly chat lupng nuac, thiic an... nham giam chi phi san xuat, tang nang suat de gop phan mang Iai hieu qua cao cho nghl nuoi luon.
Ve thiic an, luon co the sir dung nhieu loai thiic an khac nhau bi thiic an tuoi, thiic an che bien va thiic an
KHOA HOC CdNG NGHE
cong nghiep. Trong nghiem thiic thiic an cong nghiep, FCR (he s6 thiic an) la 3,68 cao ban rat nhieu so voi ket qua thuc nghiem nuoi luan bang TACN a Trung Qu6c (FCR =1,29) dugc bao cao boi Qin & CS.
(2001). Neu he s6 thirc an giam xu6ng a miic nay thi se dat dugc Igi nhuan rat cao. He s6 thiic an cao 6' nghiem thiic thirc an cong nghiep co the la do loai thiic an nay chua dat ham lugng dinh duang hoac cac bien phap quan ly thirc an chua tot. Ham lugng dinh duong t6t nhat trong thiic an nuoi luon la 35,7%
protein, 3-4% lipit, duang 24-33% va ty le E / P dao d6ng hi 31,6 den 38,9 (Liu & CS., 2000). Viec ph6i trpn thuc an che bien tir thirc an cong nghiep khong phai la giai phap t6i uu mat dii no rat tien Igi va dang dugc nguoi nuoi luon ap dung dai tra. De giam chi phi san xuat thi viec nghien ciiu cac cong thiic c h i bien thiic an tir cac nguon nguyen lieu tho san co (nhu cam gao, cam dira, bpt ca, bpt my...) Ia viec lam can thiet. Xa hon niia thi phai san xuat dugc thirc an cong nghiep chuyen diing cho luon thi nghl nuoi moi co the phat trien 6- quy mo Ion.
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Mat dp nuoi khong thich hpp se anh huong den sinh truong va ty le s6ng cua luon nuoi. Mat dp nuoi cho kit qua t6t nhat ve mat sinh truong va ty le s6ng cua luon la mat dp 0,5 kg/m^ va 1 k g / m l Toe dp tang truong ve khoi lupng cua luon 6' hai nghiem thirc nay lan lugt la 1,00 ± 0,03 g/ngay, 0,99 ± 0,06 g/ngay va ty le s6ng cua luon la 92,1 ± 2,6%, 91,5 ± 5,3%.
Tang birong vl khoi lugng khong co su khac biet giiia sii dung thiic an tuoi va thiic an che bien, gia tri SGR dat l,ll%rl,12%/ngay cao hon ban so voi sii dung thirc an cong nghiep chi dat 0,94%/ngay. Ty le s6ng trung binh cua luon khi an thiic an tuoi, che bien va thiic an cong nghiep lan lugt la 88,5 ± 5,2%, 91,5 ± 5,3%, 89,2 ± 10,4% va khong co su khac biet co y nghia (P> 0,05).
Ve mat hieu qua kinh te, nuoi a mat dp 1 kg/m^
mang Iai hieu qua kinh te cao nhat. Khi sir dung thirc an tuoi nang suat trung binh dat 6,5 k g / m ^ he s6 tieu t6n thirc an 8,4 va Igi nhuan dat 163.000 dong/m^. Khi sir dung thirc an che biln, cac chi tieu nay lan lugt la 7,9 kg/m^, 5,2 va 184.000 d o n g / m l Tir cac ket qua nghien cim cho thay mat dp nuoi luon dong t6t nhat trong mo hinh nuoi bang be bat la 1 kg/m^ (kich ca giong 40 con/kg). Thiic an cho luon la thirc an tuoi (6c buou vang) hay thiic an che bien (6c buou vang ket hpp thiic an cong nghiep).
TAI UEU THAM KHAO
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EFFECTS OF STOCKING DENSITY AND FEED ON GROWTH AND SURVIVAL OF Monopterus albus (ZUIEW, 1793) FARMING IN EXPERIMENTAL NYLON TANKS
Nguyen Huu Khanh, Ho Thi Bich Ngan Summary
The growth and survival of rice-field eel, Monopterus albus, were d'.'termined at four stocking densities (0.5, 1, 2 and 3 kg/m"') and three feeds (fresh feed, home-made feed and pellet feed) in nylon tanks. The experiment lasted 6 months. The results showed that the growth and survival of rice-field eel was affected by stocking density. The mean daily weight gain (DWG) of M. albus at density of 0.5 kg m' (1.00 g day') and 1 kg m'^ (0.99 g day"') were significantly higher than that of the other two treatments (0.86 and 0.68 g day"' for 2 and 3 kg. m"^ density, respectively) (P<0.05). The average survival rates of M. albus were 92.1%, 91.5%, 73.1% and 73.5% at stocking density of 0.5, 1, 2 and 3 kg.m"^ respectively. The DWG of rice-field eel at pellet feed treatment was significantly lower than at home-made and fresh feed treatment (0.78, 1.06 and 1.08 g day', respectively). The mean survival rates of the eel were not significantly different among treatments.
This study recommended that stocking densities < 1 kg m^ and using fresh or home-made feed are suitable for M. albus cultured in nylon tank.
Keywords: Monopterus albus, growth, stocking density, feed.
Nguoi phan bi6n: TS. Pham Anh Tuin
