Tgp chi Khoa hoc 2012 21b 19-28 Tru&ng Dgi hgc Cdn Tha
ANH HlTOfNG CUA NITRITE LEN CHU KY LOT XAC VA TANG TRLTdNG CUA TOM CANG XANH
(MACROBRACHIUM ROSENBERGII)
Dd Thi Thanh Huang" vd Cao Chdu Minh Thu^
ABSTRACT
Toxicity of nitrite (NOi) has been well documented in the culture of fishes, but not much in shrimps. In this study, freshwater prawns Macrobrachium rosenbergii (9.69 ± 1.04 g;
9.87 ± 0.48 cm) were exposed to nitrite (NOi) to determine 96h-LC5ovalue The growth, molting cycle and frequency of prawns were examined as prawns were exposed individually to 0 mg/L (control). 1.4. 2.81, 8.04 and 14.1 mg/L nitrite. The experiment was performed over a 90 day period in order to provide biological data for improving farming techniques Results showed that M. rosenbergii (9 6 9± 1.04 g; 9.87 ± 0.48 cm) were sensitive lo nitrite, the 96-h LCso of nitrite on prawns was 28.08 mg/L NO2-N. The growth (SGR) of the prawns reared in 2.81 mg/L, 8.04 mg/L and 14.1 mg/L NOi-N was significantly lower (P<0.05) than that of the control and 1 4 mg/L NO2-N treatment after 90 days The molting fi-equency ofprav.'ns reared as control and in 1 4 mg/L. 2 81 mg/L NO2-N increased. In contrast, this frequency decreased in 8.04 mg/L and 14.1 mg/L NO2-N. After 90 days, average moiling frequency of prawns reared as control and in 1.4, 2.81. 8.04 and 14.1 mg/L NO2-N was 2.8. 2.97. 2 97, 2.93 and 2.43 times, respectively, while average moUing cycle was 24.01, 23.03, 23.8. 25.4 and28.96 days, respectively. In short, nitrite is toxic for freshwater prawns M. rosenbergii although its mechanism is noi known clearly.
Keywords: Nitrite, giant freshwater prawn, growth, molting cycle
Title: The effects of nitrite on the molting cycle and growth of freshwater prawn (Macrobrachium rosenbergii)
T O M TAT
Dgc tinh cua niti'ite dd dugc tdng hgp nhieu trong nudi cd nhung rdt il doi vdi tdm. Trong thi nghiem ndy, tdm cdng xanh (Macrobrachium rosenbergii) giai doan 9,69±1,04 g;
9.87±0.48 cm duac cho tiip xuc rieng vdi nitrit (NOi) de xdc djnh gid tri LC50-96 gid. Ti li sdng, tang trudng. chu ky vd sd ldn lot xdc cua tdm duac xdc dinh khi cho tdm tiep xuc nitrit a cdc ndng dg 0 mg/L (ddi chung), 1,4 mg/L: 2,81 mg/L; 8,04 mg/L vd 14.1 mg/L.
Cdc thi nghiem dugc Ihuc hiin trong be composite co phdn thdnh 6 ngan rieng Mdi torn dugc bd tri ngdu nhien vdo mdi ngdn cua be. Thi nghiem duoc tien hdnh n-ong 90 ngdy nhdm cung cdp nhung sd lieu sinh hgc cho viic cdi ttin ky thudt nudi dgt hieu qud. Tdm cdng xanh (9,69±1,04 g; 9.87±0,48 cm) nhgy cam vdi nitrit, gid tn LCso-96 gid cua nitrit dnh hudng len tdm Id 28.08 mg/L NO2-N Tdc dg tdng truong dac biet (SGR) cua torn dugc nudi d ndng dg nitrit 2,81 mg/L; 8.04 mg/L vd 14,1 mg/L thdp hon cdy nghia thdng ki (p<0.05) so vdi tdng ti-udng ciia ldm d nghiim thirc ddi chirng vd nghiem thuc nitrit 1.4 mg/L sau 90 ngdy nudi. Sd ldn lot xdc ciia tdm a nghiim thiic nitrit 1,4 mg/L vd 2.81 mg/L gia tdng. ngugc lgi. gidm a nghiem thuc nitrit 8,04 mg/L vd 14.1 mg/L. Sau 90 ngdy nudi, sd ldn lgt xdc trung binh cua tdm a nghiem thiic ddi chung vd cdc nghiim thuc nitrit 1.4; 2,81; 8.04 vd 14.1 mg/L ldn luot Id 2 8; 2.97: 2,97: 2,93 vd 2.43 ldn, trong khi chu ky Idt xdc nung binh ldn lu0 Id 24,01; 23.03; 23.8; 25.4 vd 28.96 ngdy. Ti le sdng
' Khoa Thuy san. Truong D91 hgc Can Tho ' Tnrdng Cao dflng Cgng Dong Vuih Long
Tgp chi Khoa hgc 20l2-2lb 19-28 Truong Dai hgc Cdn Tha
cua tdm dugc nudi d ndng do nitrit 8.04 mg/L vd 14.1 mg/L thdp hem cd y nghia thdng ke (p<0.05) so vdi n I? sdng cua tdm ddi chung vd torn a nghiim thiic nitrit 1,4 mg/L vd 2.81 mg/L sau 90 ngdy nudi. Tom lgi. nitiit doc doi vdi tdm cdn^ xanh M rosenbergii mgc dii ca chi dnh hudng cda nitrit ddi vdi gidp xdc chua dugc biet rd.
Tit khda: nitrit, tom cdng xanh (Macrobrachium rosenbergii), tdng tru&ng, chu ky lot xdc
1 G i d l THIEU
Tdm cang xanh (Macrobrachium rosenbergii) la loai giap xac quati ttpng ttong nudi ttdng va khai thac thuy san d nudc ngpt CJ DBSCL, ngoat cac ddi tugng nudi pho biSn nhu cd tra, ba sa. tdm su ... thi tdm cdng xanh dugc xem la ddi tugng cd gia trj kinh tk cao va la myc tieu trong viec phat trien nudi trdng thuy san (Phuang et al., 2003). Tiem ndng san xudt tdm cang xanh rdt ldn va phong phii vdi nhieu hinh tinic nudi khdc nhau. Dien tich vd san lugng nudi trdng lien tyc tdng ttong nhimg nam gdn day. Theo Le Xuan Sinh (2008), trong nam 2005, dien tich nudi tdm cang xanh tai cdc tinh DBSCL dat 5.680 ha, san lugng udc dat 6.012 tdn, chi^m 57,7% dien tich nuoi va 94% san lugng tdm cang xanh ca nudc, den ndm 2006, dien ti'ch nudi va san lugng tiep tuc tdng manh, lan lugt la 9.007 ha va 9.514 tdn. Khi gia tang di?n tich va san lugng san pham thiiy san nudi thi van de d nhiem mdi trudng nudc, d^ic biet Id sy tich tu cac khi ddc trong cac he thdng nudi se anh hudng nhieu den cac chiic nang sinh ly, sinh hda va tang trudng ciia dpng vat tfaiiy sdn, trong do cd tdm cdng xanh.
Cimg vdi amonia, nittit (NO2") la hpp chdt nitrogen gay dpe ddi vdi dpng v^t thiiy san. Anh hudng ciia nittite da dupe nghien ciiu tren nhieu loai ca (Duangsawasdi and Sripoomun, 1981; Das et al., 2004; Yanbo et al., 2006; Dd Thj Thanh Huang et al, 2011). Tuy nhien, cac nghien ciiu ve anh hudng ciia nitrit ddi vdi giap xac, nhat la vdi lodi gidp xac nudc nggt cd gia tri kinh te cao nhu tdm cang xanh chua nhieu. De gdp phan cung cdp them dir lieu cho cac nghien ciiu sdu han cung nhu ling dung vao thyc te nudi tdm cang xjinh dat hieu qua cao. nghien ciiu anh hudng ciia nittit len chu ky lgt xac va tang trudng ciia tdm cang xanh (^Macrobrachium rosenbergii) dugc thyc hien tai Khoa Thuy San, Trudng Dai Hpc Can Tha.
2 PHlTOfNG PHAP NGHIEN c t r u 2.1 Tfadi gian va dia diem ngfaien cuu
Nghien ciiu dupe thyc hien tai Bd mdn Dinfa dudng vd ChS biSn Thiiy san, Khoa Thuy san - Trudng Dai hpc Cdn Tha tir thdng 12/2010 din thang 06/2011.
2.2 Doi tuang nghien cuu
Tdm sir dyng trong cdc thi nghiem cd khdi lugng khoang 8 - 1 2 g/con, mua tir cac ao nudi d huyen O Mdn, thanh phd Cdn Tho va dupe thudn du&ng I tudn trong b6 nhua 600 L trudc khi bd tri thi nghiem. Tom dugc cho an 2 Idn/ngay bdng thuc an vien cdng nghiep ham lupng dam > 42% (khoang 3-5% khdi lugng than) vao budi sang va kit hgp tep tuoi (khoang 10% khoi lugng than) vao budi chilu. Ngimg cho tdm an 1 ngdy trudc khi bd tri thi nghiem.
Tgp chi Khoa hgc 2012:21b 19-28 Tru&ng Dgi hgc Cdn Tha
2.3 Phirong pbap tinh nong do nitrit (NO^")
Su dung hda chat NaNO: cho vao nudc de tao NOi" \ a dya vao phirong trinh phan Iy sau: NaNO: *" Na" * NOf
2.4 Xac dinh gia tri LC50— 96 gid cua nitrit doi vdi torn cang s a n h
Thi nghiem xdc ^nh khodng nong dp gay chit cua nitrit ddi vdi tdm: Thi nghiem (tham dd) nfadm xdc dinh ndng dp nitrit cao nhat gay chit khdng qua lO^i sd ldm \ a ndng dp thdp nfadt gay chit 90% so tdm sau 96 gid tilp xiic nitrit.
Khoang ndng do nay la ca sd cho viec bd tri thi nghiem xac dinh gia tri LC50. Thi nghiem dugc thyc hien vdi 10 nghiem thiic nittit gdm 5; 20: 35: 50; 65: 80: 95:
110; 125 va 140 mg/L.
Thi nghiem xdc dinh gid tri LCso - 96 gicr cOa nitrit doi v&i torn: Thi nghiem dugc thyc hien dua vao ket qua cua thi nghiem tham dd. Chpn thyc hien vdi 8 miic ndng dp nitrit va 1 ddi chiing gdm: 0; 20; 35; 50; 65; 80 va 95, 110 va 125 m g / l . Theo ddi ho^t ddng cua tdm. ghi nhan ti Ie tdm chit d cdc thdi diim 12: 24: 48: 72 vd 96 gid. So tdm chet dugc vdt ra khdi b l nhdm tranh anh hudng den chdt lugng nudc trong b l . Cac yeu td mdi truong nhu pH. nhiet dp, oxy hda tan (DO) dugc do 2 lan/ngay vao budi s a i ^ budi chieu bdng cac thiet bj thdng thudng nhu may do pH \ a nhiet dp. mdy do o.x\. Gia tri LC50 se duoc udc tinh bdna phuang phap Probit (Finney. 1971).
2.5 Anh huong cua nitrit d cac Dong do kfaac nhau len tang t r u d n g va Idt xac ciia torn cang xanh
Tdm dugc chpn bd tri thi nghiem cd kich cd trung binh 9.69 ± 1.04 g; 9,87 ± 0.48
\'a khdng cd dau hieu benh ly. Thi nghiem dugc hh tri hoan todn ngdu nhien vdi 5 nghiem thuc gdm: 0 mg/L (ddi chiing): 1.4 mg/L ( 5 % LC5ff-96 gid) vd 2.81 mg,L (10% LC50-96 gid). day la 2 ndng dp an toan. khdng gay chet tdm va khi nudi tdm dudi ndng dp nay se khdng anh den hoat dpng sinh Iy vd di t n ^ e n ndi gidng;
8.04 mg/L (LCi—96 aid), la ndng do gay chet tdm d miic thap nhat, cd the khi nudi tdm d ndng dp nay se khdng dnh hudng den tang tnrdng; vd 14,1 mg/L ( L C H J - 9 6 gid) la ndng dp gay chet 10% tdm. khi nudi tdm d ndng do nay se anh hudng din cac boat ddng sinh ly \ a tang trudng ctia tdm. Mdi nghiem thiic dugc lap lai 5 ldn.
Mdi lan lap lai dugc bd tri trong be composite 200 L cd luoi ngan \"a sue khi nhe.
6 con tdm dugc bd tri ngau nhien \ ao 6 ngan ludi ttong mdi b l . Muc nudc trong b l dugc giu d khodng 70 - 80 cm. Thi nghiem dugc tien hanh ttong thdi gian 90 ngay.
Tdm dugc cho an 2 lan/ngay theo nhu cdu \'do liic 8 gid bang thiic an vien hdm lugng dam > 42% (3-5% khdi lugng than) \'a 16 gid bdng tep tucri (10% khdi lugng than). Hang ngay. siphon thuc an thira ra khdi he thdng thi nghiem.
Tien hanh thay 30% lugng nudc/lan sau mdi 3-5 ngdy, ndng dp nitrit dugc kiem tra (bang each thu mau nudc d timg be thi nghiem phdn tich theo phuong phdp Griess lIosva\, Diazonium) va bd sung nham duy tri ndng dp da bd tri ban ddu.
Tgp chi Khoa hgc 2012 Tntang Dgi hgc Cdn Tha
2.6 Cac chi tieu theo doi
Nhiet dp, pH, oxy hda tan (DO) dugc do 2 Idn/ngay. Can khoi lugng timg tdm d mdi nghiem thuc hang tiiang vd khi kit thuc thi nghiem. Hang ngay, theo ddi va ghi nhan sy lot xac ciia timg tdm va sd lugng tom chet d mdi nghiem tinic.
Ty le sdng (%) = 100x(sd tdm cudi thi nghiem/sd tdm ddu thi nghiem) Chu ky lot xdc: Xac dinh khoang thdi gian giira 2 ldn lgt xac k l tilp nhau.
Tang tru&ng theo ngdy: (DWG) (g/ngay) = DWG = (W, - Wo)/t Toe dp tdng tru&ng dac biet: (SGR) (%/ngay) = [(LnW, - LnWo)/t] x 100 Trong do: Wo la khdi luang tdm d thdi diim ban dau (g): W, la khdi lugng tdm d thdi diim kit thuc thi nghiem (g); t la thdi gian nudi (ngay).
2.7 Phinmg phap xir ly so lieu
Sd lieu dugc tinh gia ttj trung binh, dp lech chuan bdng phan mem Excel. Phan tich thdng ke bdng chuang ttinh SPSS 16.0 (phan tich phuang sai theo phuang phap one-way Anova. kiem djnh Ducan) d miic y nghia p<0-05.
3 KET QUA VA THAO LUAN
3.1 Doc tinh cap tinfa ciia nitrit doi vdi tdm cang xanh 3.1.1 Cdc yeu to moi tnrdng trong thai gian thi nghiem
Cac yeu td mdi trudng dugc theo doi d thi nghiem xac dinh gia tti LC50 cua nittit len torn la tuang ddi dn djnfa giira budi sang va budi chieu, khac biet khdng cd y nghia thdng ke (p>0,05) gi&a cdc nghiem thiic. Nhiet dg trung binh trong ngay la 26,71±0.05°C. pH dao dpng ttong ngay tir 7,5-7,8 va oxy hoa tan tnmg binh trong ngay la 7.6 mg/L. Cac yeu td mdi trudng tren deu nam trong khoang thich hpp cho tdm va kfadng dnh hudng den ket qua thi nghiem.
3.1.2 Gid tri LC50 ciia nitiif len torn cdng xanh
Ket qua thi nghiem cho thay gid tri LC50 thdp nhdt la 28.08 mg/L sau thdi gian 96 gid tdm tilp xiic nittit. Cac gia trj LC50 dao dpng ldn theo thdi gian tiep xiic, nhat la tir 12 gid (100,74 mg/L) din 24 gid (36,19 mg/L). Tuy nhien, cac gia trj nay biln ddng khdng ldn vd giam ddn theo thdi gian tir 24 gid din 96 gid (Hinh 1).
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Hinh I: Nong do gay doc cap tinh ciia nitrit doi voi torn cang xanh ff cac moc thai gian khac nhau
Tgp chi Khoa hgc 2012:21b 19-28 Tru&ng Dgi hgc Can Tha
Sau khi tiep xuc vdi nudc cd ndng dp nitrit cao, ti le chet ciia tdm tang manh ttong vdng 24 gid ddu, giam ddn hoac tang nhe d khoang thdi gian tir 24 den 96 gid. O ndng dp nitrit cao 95 mg/L. 110 mg/L va 125 mg/L, tdm chet 100% ngay sau 24 gid tiep xuc. nhiSu tdm chet trong tinh ttang than bj trang dye. Ngugc lai, d cac ndng dp nitrit thdp 20 mg/L va 35 mg/L, khdng cd tdm chet trong 12 gid ddu sau khi tiep xiic. Khdng xuat hien tdm chet d nghiem thiic ddi chiing trong sudt 96 gid thi nghiem (Bang 1).
Bang 1: T i le chet (%) cua torn cang xanh voi cac nong d ? nitrit kb^c nhau T h a i gian
N o n g d o Omg/L 2 0 m g / L 35mgflL 5 0 m g / L 6 5 m g / L 8 0 m g / L 95ing/L 11 Omg/L 125mg/L
12 giff 0 0 0 2 0 26,7 46,7 36,7 63,3 53,3
2 4 giff 0 10 56,7 73,3 80 90 100 100 100
4 8 giff 0 16,7
70 76.7 86.7 93.3 100 100 100
72 giff 0 23,3 73.3 80 9 0 96,7 100 100 100
9 6 gior 0 26,7 73,3 80 93,3 96,7 100 100 100 Su tuang quan ve ti Ie chet va ndng dp nitrit phii hop vdi ket qua nghien ciru ciia Amstrong et. al.. (1976) tren au triing tdm cang xanh, cac gid tri LC50 giam manh ttong 72 gid ddu tilp xiic nitrit. sau dd gia tri nay gidm nhe trong khoang thdi gian tir 72 den 168 gid. Nhieu nghien cim khoa hpc (Jensen, 1990; Chen and Cheng.
1994, 1995a, 1995b, 1996; Chen and Lee, 1997a, 1997b; Cheng and Chen, 2000) cho thay rang sau 24 gid khi tdm tiep xuc nitrit. cac chiic nang sinh ly cua tdm bi rdi loan. Cu the la nitrite khdng nhimg tt'ch tu vdo mdu ciia tdm vdi ham lupng rat cao theo thdi gian tiep xuc, lam thay ddi can bang acid — bazo va ap suat thdm thau trong mau tdm nudc ngpt Astacus astacus (Jensen, 1990), ldm gidm do pH trong mau, tang PO? va gidm oxyhemocyanin trong mdu, lam r i i loan su bai tiet nita, su dilu hda ion va sy trao ddi khi hd hap d tdm cdng xanh M rosenbergii, cd the dan din tinh trang thieu oxy, nhat la ttong dieu kien pH nudc thap (Chen and Lee, 1997a, 1997b) ma cdn tich ty trong co. gan tyy, mang, rudt trudc, mdu, tim, cudng mdt va rudt giua cua tdm sii P. monodon (29,42 ± 0,39 g) (Cheng and Chen, 2000).
Ddc tinh cdp tinh cua nitrit tren cac dpng vat thuy sdn da dugc nghien ciiu rdng rdi va dugc tdng hgp bdi Leviis and Morris (1986) va Tomasso (1994). Ddc tt'nh cua nitrit phu thupc vao loai. tudi cd va dieu kien mdi trudng n u d c . . . (Kroupova et al., 2005). Cae ket qud nghien ciiu cho thd\', tinh nhay cam ciia tdm nudc i^gt va tdm biln ddi vdi nitrit giam din theo sy tang len cua dp tudi cua tdm. Tdm nudc ngpt rat nhay cam vdi nitrit, gia tri LC50-96 gid ciia nitrit len au triing tdm cang xanh giai doan 1 0 - 1 4 ngay tudi (80 - 140 yg/con) la 8,6 mg/L (Armstrong et al., 1976); ndng do nitrit cao nhdt khdng gay chet au triing tdm la 9,7 va 1,4 mg/L ttong thdi gian 24 va 168 gid. Theo nghien ciiu ciia Chen va Lee (1997b), LC50-96 gid cita nitrit doi vdi tdm cang xanh giai doan gidng (2,52±0,20 g) la 8,49; 11.21 va 12,87 mg/L d dieu kien nong dp CF Idn lugt Id 15, 24 va 34 mg/L. Kit hgp cimg vdi ket qua ciia cac nghien ciru tren, gid tri LC50-96 gid cua nitrit ddi vdi tdm cang xanh M. rosenbergii (9,69±1,04 g: 9,87±0,48 cm) trong thi nghiem nay la 28,08 mg/L cho thay khd nang chiu dung nitrit d tdm cang xanh tang len theo dp 23
Tgp cbi Khoa hgc 2012:21b 19-28 Tru&ng Dgi hgc Cdn Tho
tudi ciia tdm. Ket qua nay cung chi ra rdng tdm M. rosenbergii it nhay cam vdi nittit han tdm nudc ngot Macrobrachium malcolmsonii, LC50-96 gid cua nittit ddi vdi tdm M. malcolmsonii giai doan gidng (10-15 g) la 3,14 mg/L (Chand and Sahoo, 2006). Trong mdi trudng nudc biln, vdi su hien dien cua ham lupng chloride (CI') cao lam giam tinh ddc ciia nitrit so vdi trong mdi trudng nude ngpt.
Theo nghien cuu ciia Chen va Chin (1988) LC50-24 gid ciia nittit len torn P. monodon la 5.00 mg/L, 13,20 mg/L, 20,65 mg/L va 61,87 mg/L tuong ung cho nauplius. zoea, mysis va postlarvae. Nhung ddi vdi tdm P. monodon giai doan gidng, LC50-96 gid ciia nitrit la 54,76 mg/L (Chen and Lei, 1990). Vdi tom P. monodon kich cd ldn facm (91,0 ± 8.0 mm), gia tri LC50-96 gid ciia nittit len tom cao hon la 171 mg/L (Chen et al, 1990b). LC50-96 gid ciia nitrit ddi vdi tdm Penaeus chinensis (39,6 ± 1,8 mm; 0,36 ± 0,06 g) la 37,71 mg/L (Chen et o/.1990a) vd ciia tdm F. penicillatus (38.5 - 47.5 mm) la 38,52 mg/L va 40,85 mg/L d nong dp muoi ldn lupt la 25%o va 34%o (Chen and Lin, 1991). Tdm L. vannamei gidng (56 i 9,6 mm) cd kha nang chju dung dp ddc cua nitrite cao han cdc loai tdm bien neu tten. LC50-96 lan lugt la 76,5; 178,3 va 321.7 mg/L d nong dp muoi 15%o; 25%o va 35%o. (pH 8.02, nhiet dp 18°C) (Lin and Chen, 2003).
Nhu vdy. thdy kha ndng chju dyng nittite d tdm penaeid ciing tang len theo dp tudi cua tdm va cao hon so vdi tdm nudc ngpt M. rosenbergii.
3.2 Anh hirdng ciia nitrit ten tang trudng va lgt xdc cua tdm cang xanfa 3.2.1 Cdc yeu to moi truang trong qud trinh nuoi sinh trudng
Cac yeu to mdi trudng trong thdi gian thi nghiem nudi tang trudng la kha dn djnh, cac gia tti tmng binh khdc biet khong cd y nghTa th6ng ke (p<0,05) giira cac nghiem thuc. Nhiet dp giiia cdc nghiem thiic cd miic dao ddng thap ttong khoang 26.74 ± 0.09°C vdo budi sang va 27,26 ± 0,15°C vdo budi chieu, gia tri pH trung binh ttong ngay la 7,78±0,12, oxy hda tan (DO) trung binh trong ngay la 5,69 ± 0,06 mg/L. Cac yeu td mdi trudng tten deu nam trong khoang thich hgp cho sy phat ttien ciia tdm vd Ididng anh hudng din kit qua thi nghiem.
3.2.2 So ldn lot xdc vd chu ky lot xdc
Sd Ian lot xac cua tdm d nghiem thirc nittit 1,4 mg/L va 2,81 mg/L la bdng nhau va nhieu nhat, trung binh dat 2,97 ldn va cd bieu lii?n giam dan d nghiem thiic cd ndng dp nitrh cao 8,04 mg/L (2,93 lan), tuy nhien khac biet khdng cd y nghTa thong ke (p>0,05) so vdi d nghiem thirc d6i chiing (trung bmh 2.8 lan). Rieng d nghiem thiic riitrit 14.1 mg/L, so ldn lot xac it nhdt (trung binh 2,43 lan), khac biet CO y nghTa thdng ke (p<0,05) so vdi d nghiem thiic ddi chiing va cac nghiem thuc ndng dp nittit thap cdn lai (Hinh 2a).
Chu ky lot xac cua tdm d nghiem thiic nittit 1,4 mg/L la ngdn nhdt (ttoing binh 23,03 ngay), ngdn ban so vdi d nghiem thiie ddi chung (trung binh 24,01 ngay), nhung khdc biet khong cd y nghTa thdng ke (p>0,05). Ngupc lai, chu ky Ipt xac tang ddi ra d k tti nghiem thirc nitt-it 1.4 mg/L (23,03 ngay) din nghi?m thirc 2,81 mg/L (23,8 ngay) va 8,04 mg/L (25,4 ngay). nhung khac biet khdng cd y nghia thong ke (p>0.05). Rieng d nghiem thiic nitrit 14,1 mg/L, chu ky lot xac dai nhat la 28,96 ngay, khac biet co y nghTa thdng ke (p<0,05) so vdi d nghiem thiic doi chimg va cdc nghiem thurc ndng dp nitrit tiidp cdn Iai (Hinh 2b).
Tap chi Khoa hgc 20l2'21b 19-28 Tru&ng Dgi boc Cdn Tho
Ji,
X
Hinh 2: So lan lot xac (a, trai) va chu ky lot xac (b. phai) ciia tom cang xanh a cac nong dp nitrit khac nfaau sau 90 ngay nuoi
Cac yeu mdi trudng nhu anh sang, nhiet dp kich thich he thdng thdn kinh trung ucmg va nai chiia hormone kich thich lot xdc, se tac ddng len chu ky lot xdc ciia giap xac (Wassenberg and Hill, 1984). Nitrit d ndng dp thdp dudi ngudng gay chit cung la mpt yeu td mdi trudng kich thich tdm lot xdc nhieu lan. Ket qua thi nghiem (Hinh 2b) cho thdy chu ky lot xdc cua tdm d nghiem thuc nitrit 1.4 mg/L la ngdn nhat, do tdm d nghi#m thiic nay Ipt xdc nhieu Ian nhat. Ndng dp nitrit thap cd the anh hudng den sy lot xac cua tdm nudc ngpt .\{. rosenbergii va cua C. sapidus (Armstrong et. al, 1976; Manthe el al. 1984). Trong nghien curu ciia Chen \ a Chen (1992b), sd lan lot xac cua tdm sii giai doan gidng (1,40 ± 0,05 g; 6,30 ± 0,07 cm) tang dan d cac nghiem thiic 0; 2; 4; 8 vd 20 mg/L nitrit. sd lan lot xdc trung binh la 6.27; 6,30; 6,34; 6,92 va 7,14 ldn ldn. Ket qua thi nghiem cung cho thdy, ndng dp nitrit cao nhat chap nhan dupe ddi vdi sy lot xac ciia tdm su la 2 mg/L. Hoat ddng Ipt xdc gdn lien vdi sy tang trudng vd sy phdt trien ciia tdm. Tuy nhien. chu ky lot xdc ciia tdm cdn tiiy thudc vao giai doan tdng trudng, tinh trang sinh ly, dieu kien dinh dudng, dieu kien mdi trudng (Yujiroh. 2010).
3.2.3 Tang tru&ng theo ngdy (DWG) va dgc biit (SGR) ciia tdm cdng xanh K i t qua thi nghidm cho thay tdng trudng theo ngay (DWG) ciia tdm d nghiem thiic nitrit 1.4 mg/L d^t trung binh 0.11 g/ngay, tuang duang vdi tang trudng ciia tdm d nghi?m thijtc ddi chiing. Tang trudng dieo ngay ciia tdm cd gia trj thdp nhat d hai nghiem thiic nitrit 8.04 mg/L va 14,1 mg/L la 0.07 g/ngay, khdc biet cd y nghTa thdng ke (p<0.05) so vdi d nghiem thue ddi chimg. Tang trudng dac biet (SGR) cua tdm d cac nghiem thiic giam dan theo su gia tang eiia ndng dp nittit thi nghidm. CJ nghiem thiic nitrit 1,4 mg/L. SGR ciia tdm dat trung binh 0,75 %/ngay va d doi chiing la 0,76 %/ngay. Tdc do tang trudng SGR cd gia tri thap nfaat d hai nghiem thiic nitrite nong dp cao 8,04 mg/L va 14,1 mg/L lan lupt la 0.55 %/naa\
vd 0.52 %/ngay, khac biet cd y nghTa thdng ke (p<0,05) so vdi d nghiem thiic ddi chiing. Tac dpng dudi ngudng gay chet ciia nitrit trong mdi trudng nudi cd the lam gidm tang trpng cua tdm vi tom phai phan bd ndng lugng cho boat ddng cua cdc ca quan nham giiip ca the chdng lai tac dyng ddc ciia nitrit. Nhieu ket qud nghien ciiu cho thdy tang trudng va phat ttien ciia tdm gidm theo sy tan^ len ciia ndng dp nitrit trong mdi trudng nudi. Khi cho au trimg tdm cang xanh tiep xiic vdi cac ndng do nitrit tir 0, 2. 4. 8 va 16 mg/L. ket qua la d ndng dp nitrit cao 16 mg/L, 4u trung pha 1 chet toan bd va au trimg pha 2 ngimg phdt trien d giai do?ii 10 (Mallasen and Valenti, 2006). 6 ndng dp nitrit 6.4 mg/L ldm gidm 50% tang ttudng ciia du tning 25
Tap chi Khoa hoc 20I2:2lb 19-28 Tniong Dip hoc CSn Tha
torn p. mdicus a dp man 30%o, a pH 8.0 va 2 8 X sau 34 ngay (Wickins, 1976).
Theo Chen er. al., (199bc) 6 n6ng do nitrit 21,38 mg/L lam giam 50% kh6i luong cua torn P. monodon giai doan giSng (0,26-0,51 g) 6 dp man 20%ii va 27°C. Theo nghien ciiu ciia Chen va Chen (1992) thi nitrit nong do 17.41 mg/L va 22.45 mg/L lam giam 50% tang tmong (ECjo) cua tom su gi6ng (1,40 ± 0,05 g; 6,30 ± 0.07 cm) sau 20 va 60 ngay nuoi.
- &14- 0.11 o n
-I DH f ] pi
1102 H
I •"' 0
I 2jtl t M 14.1 ait H U'nx aJifkita l « ^ l
X I 1 X X
1,4 2 81 8.CM W-l VoDg dg nitnlc Ihi D>hijoi (m^/L)
H i n h 3 : T o e d $ t 5 n g t n r d n g t u y f t d o i ( D W G ) <a, t r a i ) v a t u v n g d o i ( S G R ) ( b . p h a i ) v e k h o i l u v n g c u a t 5 m c&ng x a n h v c a c h a m l u n u g n i t r i t e k h d c n h a u s a u 9 0 n g a y n u o i
Nghien cuu ciia Chen va Chen (1992) ve anh hudng ciia nitrit len chieu dai ciia torn su gidng (1,40 ± 0,05 g; 6.30 ± 0,07 cm), k^t qua cho thdy su tiSp xuc vdi nitrite ndng dp 4 mg/L da ldm gidm 5% vd 6,7% chieu dai ciia tdm sau 30 va 60 ngay, trong khi vdi ndng dp 16,14 mg/L va 26.20 mg/L ldm giam 50% sy tang chieu dai cua torn (ECjo) sau 20 va 60 ngay nudi.
Ket qua thi nghi?m (Hinh 3) cd the giai thi'ch rang, d nong do thap 1,4 mg/L (5%
LC50-96 gid) dupe xem la an toan ddi vdi tdm cang xanh thi nitrit mang y nghTa la yeu td moi trudng kich thich sy lot xac ciia tdm do tdm bi sdc nhieu ban la do nhu cdu tdng trudng. Tdc do tang trudng (SGR) ve khdi lugng va chieu dai d nghiem thuc nitrit 2.81 mg/L khdc biet cd y nghTa thdng ke (p<0,05) so vdi tang trudng eiia tdm d nghiem thiic nitrit 1,4 mg/L vd nghiem thiic ddi chiing. KSt qua nay cung phil hgp vdi khuyin cao cua New (2002), trong ao nudi tdm cang xanh, ndng dp nitrit nen < 2 mg/L.
4 KET LUAN
Tdm cdng xanh nhay cam vdi nittit, nong dp nitrit gay chet 50% tdm sau 96 gid thi nghiem la 28,08 m g ^ . Sd Ian lot xdc cua tdm tang (chu ky lgt xac ngdn) d nhimg nghiem thiic nittit ndng dp tiiap 1,4 mg/L va 2,81 mg/L va giam ddn (chu ky lot xac ddi) d nhCmg nghiem thirc cd nong do nitrit cao 8,04 va 14,1 mg/L. Tdng ttirdng theo ngay ya tang trudng ddc biet cua tdm d cac nghiem tiiuc giam ddn theo sy gia tdng cua ndng dp nittit thi nghiem; ngay d ndng dp nitrite 2.81 mg/L tang ttvdng ciia tdm da cd sy khac biet cd y nghia thong ke (p<6.05) so vdi doi chiing.
Ttp chi Khoa hgc 2012:21b 19-28 Tnrdng Dai hgc Cdn Tha
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