Tiiu ban Sinh thdi, Moi tricdng vd qudn ly Biin
NGHIEN c u t ) QUY LUAT SINH TRU'OfNG CUA LOAI NGHEU {Meretrix lyrata) 6 CU'A SONG BACH DANG VA Y N G H I A CANH
BAO MOI TRU'OfNG Le Xuan Sinh, Tran Dire Thanh, Dang Kim Chi Vien Tai nguySn vd Mdi trudng bien, 246- Dudng Da Ndng - Hai phdng
Email: [email protected]
Tdm tat
Ddc trung chdt ddy cua bai nghiu viing ndm d hai bin bd cua sdng Bgch Ddng thudng la cdt pha biin hinh thdnh do si^ tuong tdc giiia dong chiiu vd ddng chdy cica sdng. Ddng chdy cua nude vita phdi vd dugc dip nhdn bdi nguon dinh duang ddi ddo tu luc dfa tgo nen cdc bdi triiu thugn lgi cho su phdt trien cua con Nghiu. Nhu vdy, vdi cdc dgc diem thuy hda, ddng chdy md quy trinh nuoi Nghiu d cica sdng Bgch Ddng cd mgt sd dgc diem rieng so vdi cdc khu vuc khdc nhu kich ed con ^idng, thdi gian thd gidng. Quy lugt phdt triin ciia nghiu tuong icng giica tuoi sinh trudng vd kich thudc vd dugc xdc
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dinh theo cong thuc Id: y (thdng tudi) = e ' °-' . Cdc giai dogn phdt trien cua nghiu chiu su tdc dgng cda moi trudng, vi vdy quy lugt sinh trudng cda Ngheu chi thi SIC thay ddi mdi trudng.
Abstract
STUDY ON GROWTH OF CLAM (Meretrix lyrata) AND ITS ENVIRONMENTAL INDICATION IN BACH DANG ESTURY The characteristics of the clam ground substrate on both sides of the Bach Dang estuary is usually muddy-sand formed by the interaction between tidal and river flows. The medium flow receiving the rich nutrients from land created the tidal flats which were suitable for the clam growth. Thus, there were the special features in the process of clam culture in the Bach Dang estuary which differed from the other areas to fit with the flow and-hydro- chemistry characteristics in the area, such as size of breeding clam and time for stocking. The growth of clam correspondence between age and size of the
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shell is determined by the formula: y (months) = e ""* . The growth stages of clam had been affected by the environment variations, so the clam growth indicated for the changes of environment.
Hgi nghj Khoa hgc vd Cdng nghe biin todn qudc lan thu V
1. Md d^u
Viing cua sdng Bach Ding thudc kieu vung cura sdng hinh pheu vdi hai bSn bd phdn bl cac bai trieu, Id dia hinh quan trpng nhat trong cdc dang dia hinh bi ngap nude theo chu k^
trilu. Bai trilu thudng la cat pha bun cd cac tilu hoan luu hinh thanh do sy tuong tac giiia ddng chilu va ddng chay cua sdng [2] .Vdi ngudn dinh duang phong phii do ddng chdy mang tii lyc dia ra vung cdra sdng nSn ngheu Ben Tre dugc nudi X^i day dang phdt tri&i manh. Chua cd nghien cuu ndo vl quy luat sinh trudng cua con Ngheu ma chi do kich thudc Ngheu theo nghien c ^ nhd 16 va danh gid chi thi mdi trudng ciia con Ngh§u.
Vi ddc dilm chit lugng nude, bai trieu, trao ddi nude d khu vyc cua sdng Bgch Ding co net rieng so vdi vung chdu' thd nhu bai Ngh6u Nam Dinh ndn con ngheu tai ddy phat triin theo quy luat ri^ng. Dl xdc djnh tu6i Ngjieu thdng qua kich thudc vd md khdng cin phdi phan tich sinh hpc la nghien ciiu rat cd y nghia trong khoa hpc va thyc tien, nhdm tang ndng suat vd cd giai phap phdng tranh cdc tac ddng xdu cua mdi trudng.
2. Phinmg phdp 2A. Tdilifu
Cdc sd lipu trong bai bao nay dugc trich tir dl tai ludn an tien sT "Nghien ciru khd nang tich liiy thiiy ngdn trong ngheu Meretrix lyrata tgi khu vuc cua song Bgch Dang" va lugn van thac sT tir nam 2009 din nam 2011 tai khu vuc xa Ddng Bai, huyen Cdt Hdi, Hdi Phdng.
2.2. Phittmgphdp
- Phuang phap nudi nghSu ngoai hien trudng theo Sd tay hudng din nudi ngheu cua MCD, 2009 [3].
Do kich thudc n ^ e u bang thudc Panmer, cdc kich tiiudc can do Id: chilu dai x chieu rdng x chieu cao (mm).
- Xac dinh quy luat sinh trudng cua Ngjieu theo phuang phdp binh phuang tdi thilu phdn tich ANOVA bing phin mlin Excel 2003.
Hinh l:Khu vuc nuoi ngheu dphgm vi cua song Bgch Ddng
3. Ket qua
3.1. Mgt so dac diem chd yeu cua moi tnrdng bai nuoi ngheu
- Nhiet do: Ket qua quan trie nhift dp nude ciia bai nudi Ngh6u trong 12 thing (ti thang 6/2010 din thdng 5/2011) cho gid tej dao d^ng tii 15°C din 34°C, nhipt dd trung binh la25,rc.
Tieu ban Sinh thdi. Moi tncdng vd qudn ly Bien
' Do mudi: Vao mua mua, dp mudi trong nude tai bai Ngheu thap (5%o), mang tinh chat cua khdi nude lg nhgt. Vao miia khd, dp mudi cua nude tang cao din 30%o, mang tinh chit ciia khdi nude lg vua.
- pH: pH ciia nude khu vyc sdng Bach Dang cd gid trj dao dpng tir 6,4 din 8,3, trung binh la 7,6. Nhan dinh nay phii hgp vdi cac ket qua nghien cuu tnrdc day [4,5],
- Chdt ran la licng: Ham lugng chat rin la lung khu vuc ciia song Bgch Ddng kha cao, dao dpng khoang 159,1- 1383,2 mg/l, trung binh la 667,2 mg/l. Trong nga;^, TSS dao dpng Idn, tir 195 mg/l den 935 mg/l (vdo miia kho), trung binh la 440mg/l.
Vdo miia mua, TSS trong ngay dao dpng khoang 159,1 - 1383,2 mg/l, trung binh la 666 mg/l. Nhu vay, ham lupng TSS trong nude rat cao vd bi chi phdi theo miia kha ro rang.
D ^ l EW! E W J ' E W * BOI5 EM6 B o " BWB B^rS t W l S j E W l ' W H (UBI (27IR |27ff|,(SM) |27S) ,(30(10] (V12). i a i | , (37/1] | M ) [lit] (6(5)
Hmh 2: Bien thiin hdm lugng TSS trong nude tgi bdi Nghiu thi nghiim
- Thdnh phdn cdp hgt ciia bdi nudi Ngheu: Dang tram tich deu la loai cat nhd theo ty le 75:24. Cac thdng so phan tich, thanh phan cap hat trdm tich bai Ngheu kha phii hpp vdi nudi Ngheu [1,3,6].
3.2. Diic diem cita quy trinh nuoi Ngheu d kbu vire cua song Bgch Ddng
Ddng chay cua khu vyc cira sdng Bach Dang quyet djnh phuang phdp nudi Ngheu tai day. Dudi day Id mgt sd dgc diem khac biet so vdi viing nudi nhu Nam Dinh:
- Cdi tgo bdi: Ddi vdi bai trieu thap cd ty le bim Idn khoang 30-40% thi dugc bom cat vao bai, dp day cua Idp cat 15 cm la thich hgp, Tuy nhien day la Igch tau nen viec bom cdt CO th§ lam sa bdi luong ma nha nude hang nam phai bd nhieu tien de nao vet.
- Thdi gian thd gidng: Hien tai Ngheu gidng dugc thd tap trung vdo mdt dgt bat dau tir thang 5 am lich, trdnli thd gidng vdo cdc thang 3 va thdng 4 am lich vi Ngheu thudng bi chet hang loat. Tuy nhien lai xay ra hien tugng khan hiem Ngheu gidng, dan den khong kiem soat dugc chit lugng nguon gidng. Khi Ngheu dat kich thudc thuong pham ciing liic lam gidm gia mua va nliu cau tieu thu khong dap iing dugc het.
- Cd Ngheu giong: Kich cd Ngheu gidng tdt nhat la khoang 400-500 con/kg. Chiing toi da tien hdnh thi nghiem tha Ngheu gidng - Ngheu tdm (2-3 nghin con/kg) va ket qud la gilng bi phdt tdn 100%.
- Thu hogch: Chu yeu sir dung cdo thii cdng de thu hogch Ngheu, trong khi tai Nam Dinh ngudi ta dung thuyen may'de khai thdc. Ngheu thu hoach tai day cd trpng lugng khodng 45 -50 con/kg. Thdi gian thu hogch dien ra tir thang 2 din thdng 5 duong lich.
Hdi nghj Khoa hgc vd Cdng nghi biin todn quoc Idn thic V
3.2.1. Su tdng trudng kich thudc cua Ngheu tic khi thd giong den thu hogch
Su tang trudng kich thudc cua Ngheu trong mgt vu nudi 12 thang, kl tir khi tha gidng din khi thu hoach, dugc trinh bdy tren hinh 3 dya vao kit qua do dac kich thudc vd Ngheu hang thdng tai cac d thi
nghiem, vcd s6 lupng 80 con. ^.^^ ^. ^..^ ^^..^ ^.^^ ^^^^^ ^ „ ^ j , „ ^ ^^^ j ^ ^ ^ . ^ tgi khu vifc cua song Bgch Ddng
Tu kit qua nghien cim cho thiy, biin ddng kich thudc ciia Ngheu tu Iiic tha giong den trudng thanh nhu sau: chilu ddi hi 2,12 - 4,05 cm; chilu rdng tii 1,78 - 3,29cm; chilu cao tir 1,1 den 2,16 cm.
Kit qua phan tich ANOVA giira ba nhan td (chilu dai, cao vd rdng trung binh) ciia Ngheu tai ciia sdng Bgch Ddng cho F =33 < F^nx. = 3.28 chip nhan Hi la cd sy sai khdc ve quy luat phdt triin giua cdc kich thudc khdc nhau cua N ^ e u dugc do. Nen quy ludt sinh trudng giiia thang tudi va kich thudc tuy thu0c chpn biSn sd chieu dai, chiSu fOng hay chieu cao.
3.2.2. Xir ly so lieu va tim quy lugt
Theo dieu tra khdo sat thyc te Ngheu gidng tha tai cac bai nudi d ciia song Bgch Dang Id 6 thang tudi, qua phdng nudi va ba giai doan uom gidng.
Kich thudc do t^ dgt 2 (Ngheu dugc 8 thdng tudi) cd tdc dp phdt trien chgm la do Ngheu mdi dugc tha trong 1 thang can cd thdi gian lam quen vdi mdi trudng tai ciia sdng Bach Dang. Nhu vgy, tdc do phat trien cua NghSu dot nay khdng phan dnh chinh xac toe dp sinh trudng cua Ngheu nudi tai day nen logi bd sd lieu nay.
Xac djnh dugc quy luat phdt triin NghSu vd kich thudc theo chilu ddi, chieu rgng hogc chieu cao dugc the hien nhu sau:
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y (thang tudi) - e '^<*^^ = (3.1) Trong do: D - Chieu ddi (cm); R - Chieu rdng (em); C - Chilu cao (cm).
Ket qud kiem tra sai sd khi tiiih thang tudi theo kich thudc vd cua Ngheu dugc the hien tren bang I.
Bdng I. Sai sd phdn trdm (%) tinh tudi Ngheu theo cdc kich thudc khdc nhau
Thang tuoi tinh theo chieu dai (%) Thang tuoi tinh theo chieu rong (%) Thang tuoi tinh theo chiSu cao (%)
Sai sd trung binh 7,2 7,1 6,6
Tieu ban Sinh thdi, Mdi tncdng vd qudn ly Biin
Nhu vdy, sai sd tnmg binh tudi Ngheu tinh theo chieu rdng la thip nhit (6,6%) nSn
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cdng thiic y (thdng tudi) = e ^'^ (3.2) dugc xdc dinh dl xac dinh tudi Ngheu theo Hch thudc vd.
4. Thao lu^n 4.2. Cong thuc 3.2
Cdng thiic nay cho thiy quy ludt phat hiln cua Ngheu ^iua tudi va chilu cao theo ham sd ma. Nhu vdy, tiiy vdo hing giai doan vd din nguong nhit dinh thi Ngheu Idn chgm nen Ngheu d day thudng dugc thu hoach sau 1 ndm nudi.
So sanh vdi kit qud nghiSn ciiu cua Trucmg Qudc Phu ddi vdi Ngheu Ben Tre nudi tai' cdc bai trilu tai miln Nam cd thiy ring, quy ludt cung biin thien theo hdm so mu. Tuy nhien, khi kiem tra cdng thiic nay ddi vdi Ngheu nudi d ciia sdng Bach Ding cho kit qud khdng phu hgp.
Nhu vdy, tiiy thugc vao dilu kien tu nhien ma quy ludt phat triin ciia Ngheu la khac nhau tgi cac vimg miln.
4.2. Tdc dgng cua moi trwdng tdi quy lugitphdt trien cua Ngheu
Ket qud nghiSn ciiu cho thay, qua trinh phat trien cda Ngheu d viing nghiSn ciiu cd thi chia ra 3 giai dogn. Tir thang 6 den thang 10/2010 Ngheu Idn nhanh (giai dogn 1) vd Idn cham tCr thdng 11/2010 din thdng 1/2011 (giai doan 2), sau dd Ngheu Idn nhanh d giai dogn thu hoach tu thdng 2 din thang 5/2010 (giai dogn 3).
a. Giai dogn 1
Giai doan I (sau mpt thang ke tii khi thd gidng - thang 7) NghSu cd tdc'dO Idn chgm (hinh 3).
Sd dl nhu vay cd the la do Ngheu dugc tha tir cdc hd uom gidng ra bai nudi nen ed su thay ddi ve mdi trudng ddt nggt, dilu nay ddi hdi Ngheu phdi cd thdi gian thich nghi. Sau do, tii thang 7 din thang 10/2010, Ngheu Idn rat nhanh. Sy phat trien ve chieu rpng dugc nhan biet qua man sac vd va vdn sinh tnrdng.
Hinh 4: Vach phdn chia syc sinh trudng ciia Ngheu
Giai dogn ndy Id mua mua, nude sdng mang nhieu vgt chat dinh dudng tii lyc dja ra ciia sdng lam cho ngudn thiic an phong phii. Ham lugng TSS trong cac thang 7, 8, 9 cd gid tri trung bmh tu 731 din 875 mg/l, gia tri cue dgi trong thdng 8 dat 1382 mg/l.
Hdi nghi Khoa hgc vd Cong nghi biin todn quoc lan thir V
Hinh 5: Tuyin nhdn trong rugt Ngheu b. Giai dogn 2
Kit qua giai phdu N ^ e u trong giai doan nay cho thiy co the Ngh6u tilt ra tuyln nhdn (hinh 5). Ddy la bilu thi sinh Iy cua NghSu khi bi dnh hudng cua mdi trudng. Xdc suit cd mgt cua tuy6n nhdn trong rugt Ngheu Id 98%. Tuyln nhdn cd mau hdng trong sudt dai 1cm hinh siing trau. Theo nghi&i ciru cua Truang Qudc Phti (1999), ddy la mgt trong nhung bilu hien ciia sy trao ddi nude kem khi liiuy trilu nit luc nude diing ho|Lc ddng chay cham.
Hipn tugng ndy xdy trong giai doan miia khd khi ma sdng gid da keo cdc vgt chat dmh dudng ra biin, ngudn dinh dudng cung cap tii dat lien thap, liie hien d chd ham lugng TSS trong cac thang II, 12 trung bmh Id 355-392 mg/I, thip so vdi trung binh cua cdc dgt Idido sat (hinh 2).
Day la diu hieu chi thi mdi trudng ciia Ngh6u dl cdc hg nudi cd giai phap phdng tranh phu hgp, cy the nhu:
- Dan mat do Ngheu d nhiing vj tri cd Ngheu phan bd day.
- Chuyen Nghdu phan bd d phia bai trieu cao xudng phia bai trieu thip.
c. Giai dogn 3
Giai doan 3 (tii thang 2 din thdng 5): NghSu phat trien tdt hon giai dogn 2. Ddy la giai dogn cd the thu hogch Ngheu khi khdi lugng dgt tii 68 den 52 con/k^. C giai doan 3 Ngheu da dat kich thudc thuong phim nSn ed khd chdng chiu vdi sy thay ddi mdi trudng (thdng 2- 3 am lich). Vao thdi diem ndy ngudi ta khuyen cao khdng nen thd gidng vi kha nang chong chiu su thay ddi mdi trudng cua Ngheu con thudng thdp. Dac bipt la giai doan mua philn nen trong khoang thdi gian phoi bai Ngheu thudng bi anh hudng ciia nude nggt, dan den hien tugng sdc va chet.
5. Ket lu|n
Vdi cdc ddc tnmg thiiy hda, ddng chdy dac thu ma quy trinh nudi Ngheu d cua song Bgch Dang cd mdt sd dgc dilm rieng so vdi cdc khu vuc khac nhu kich cd con gidng, th6i gian thd gidng.
Quy ludt phat trien ciia Ngheu tuong iing giua tudi sinh trudng vd kich thudc vd. Sai so trung binh tudi Ngheu tinh theo chilu rpng la thdp nhat (6,6%) nen cdng thiic dugc sit dung dl xac dinh tudi Ngheu theo kich thudc vd Id:
y (thdng tudi) = e • "^ trong dd C: la chieu cao ciia vd.
Tieu ban Sinh thdi, Moi tru&ng va quan ly Bien
Qua trinh phat trien cua Ngheu c6 bao giai d o ^ tuong ung voi sir tac dpng cua moi trucmg. Nhu vay, quy luat sinh trucmg cua Ngheu chi thi s\r thay d6i moi trucmg.
6. L61 cam on
Tac gia xin cam on su giup do tan tinh cua thiy, co giao huong din (GS.TS Dang Kim Chi, PGS.TS. Trin Diic Tlianh), cua can bp Vien Tai nguyen va Moi tru&ng bi2n va cac hp dan Ichu vuc xa Dong bai, huyen Cat Hai, Hai Phong dS tac gia hoan thanh nghien cuu nay.
TAI Lieu THAM KHAO
1. Truang QuAc Phii, "Nghien ciiu mot so dac diem sinh hpc, sinh hoa vd ky thugt nuoi ngheu Meretrix lyrata (Sowerby) dat nang sudt cao ", Luan an TiSn sT, Dai hoc CJn Tho, (1999).
2. Trjn Diic Thsinh, Nguyin Cin, Dang Diic Nga, "Bdn chdt cdu true estuary ciia viing cira song Bach Bdng", Tuyen tap tai nguyen moi truang biSn, tap VII, pp 35-50 (2000).
3. Trung tam bao t6n Sinh vat biin & Phat triin Cong ddng (MCD), S6 tay hicang ddn ky thugt mm ngao, Ha Npi. Viet Nam (2009).
4. Cao Thi Thu Trang, Le Xuan Sinh va nnic, "Bdo cao tdng kit di tdi: Bdnh gid sue tdi mdi tncdng cm sdng Bgch Bang vd de xudt cdc glal phdp bdo ve moi iruang, phdt triin ben viing", Luu trii tai Thu vien Vi|n Tai nguyen va Moi trucmg biin, (2009).
5. Cliu Van Thupc, Bao cao Ichoa hpc ting Icit Nhiem vu HTQT Vlet-Phdp "Nghiin cm anh huong nhdn sinh vd thity dgng luc t&i cdc qudn xd thuc vdt phii du vd vi khudn ", Lim tru tai Thu vien Vien Tai nguyen va Mpi truang biin (2010).
6. Nguyen Huy Yet, "Bdo cdo tong ket de tdi: Nghien cuu hien trgng vd cdc gidi phdp bdo ve vdphdt trien viing ngheu giong ven bien Nam Binh", Lim trii tai Thu vien Vien Tai nguyen va Moi truang bien (2008).
Ngtr&i dgc nhan xet: TS. Chu Van Thuoc
