Boleng jwa metsi bo botlhokwa mo bolemiruing jwa tlhapi ya metsi a a foreshe (temôthuo ya ditshelametsing) mo Afrika Borwa ka ge bo netefatsa tikologo e e itekanetseng ya metsi go tlhapi.
Boleng jo bo siameng jwa metsi bo rotloetsa kgolô ya ditlhapi (metsi a boleng jo bo siameng = kgolô ya ka bonako), go runya ga malwetse ga mmogo le tatsô le mmala wa tlhapi. Boleng jwa metsi bo sweetswa ke mabaka ale mane a magolo:
Themphoritšhara ya metsi
Dielô tsa oxygen mo metsing
Dielô tsa ammonia mo metsing
pH ya metsi (seêlô sa boesiti kgotsa bo-alkaline)
Mathata ale mantsi a boleng jwa metsi ka bolemirui jwa tlhapi ya metsi a a foreshe ke ka ntlha ya phokotsego ya oxygen, dielô tsa ammonia tse di kwa godimo kgotsa dielô tsa pH tse di kwa godimo. Mathata ano a amana thata le dielô tsa bolêlê jo bonnye mo metsing.
Kgolo ya bolêlê jono e ikaegile mo selekanyong sa dikotla - nitrogen (N) le phosphorus (P) - mo metsing. Dikotla tseno di tsena mo letamong ka:
Metsi a motswedi (go elela ga metsi go tsena mo letamong).
Go tsena ga maraga ka motsi wa tshologo e e maatla ya dipula (kêlêlo).
Sefepi sa tlhapi ka paka ya tlhagiso.
Themphoritšhara ya Metsi mo Bolemiruing jwa Tlhapi
Trout gantsi e gola ka bontle magareng ga 14 le 18°C (themphoritšhara ya metsi e e gaisang ke 16°C) fela ditshidi tse di bothitho jaaka sharptooth catfish di gola sentle mo metsing a a bothitho (20 - 30°C) mme tilapia e ithatela dithemphoritšhara tsa metsi tse di kwa godimo go feta tsa 24 - 34°C.
Trout e tshaba metsi a a bothitho. Dithemphoritšhara tse di kwa godimo ga 20°C di baka gore trout e emise go gola mme di tlile go baka mathata a mangwe a tlhagiso, jaaka matshosetsi a a oketsegileng a malwetse le mathata a oxygen, go tlhalosa Henk Stander, molaodi-mogolo wa setegeniki wa Aquaculture: Department of Animal Sciences, Stellenbosch University.
Mathata ano (koketsego ya matshosetsi a malwetse le phokotsego ya oxygen) a bakwa gantsi ke bolêlê jo bontsi mo metsing a a bothitho. Fela fa dithemphoritšhara di sena go fitlhelela 21°C le go feta, tlhokomelo e e kgethegileng e tshwanetse go ka tsewa go thibela dintshu tsa ditlhapi le go mela ga bolêlê. Bolêlê bo bakwa ke koketsego ya palo ya bolêlê jo bo mmala wa loapi le botala, jo bo kgotlhiwang ke dithemphoritšhara tse di kwa godimo le go nna teng ga dikotla. Bolêlê bo golola metswako ya khemikhale e e jaaka sere se se nkgang jaaka mmu, geosmin. Sere seno se monyelwa ke tlhapi mme se fetole tatsô ya nama ya tlhapi.
Dielô tsa Oxygen mo Bolemiruing jwa Tlhapi
Dielô tsa oxygen tsa metsi mo bolemiruing jwa tlhapi ya metsi a a foreshe di tshwanetse go nna 5 mg/L le go feta ka dinako tsotlhe. Fa dielô tsa oxygen mo metsing di le kwa tlase, ditlhapi ga di kitla di kgona go hema sentle mme di tlile go tsenwa ke kgatelelô.
Mathata a oxygen a bakwa gantsi ke bolêlê jo bonnyennye. Bolêlê jono jo bo nnyennye bo itirelanjo mme bo tlhagise oxygen. Ka dielô tse di tlwaelegileng tsa bolêlê jono, ga go kitla go nna le mathata.
Fa dielô tsa bolêlê jono di okotsega, dielô tsa oxygen mo bosigong di nna kwa tlase ga 5 mg/L mme go tlile go nna le mathata a oxygen mo metsing mo mesong.
Sabobedi, fa bontsi jwa bolêlê jo bo nnyennye bo swa ka tshoganyetso (ka ntlha ya maêmô a bosa a a maru kgotsa go gaswa ga dibolaya-bolêlê), aerobic bacteria e tlile go gola ka maatla go thusa go bodisa bolêlê jo bo suleng. Aerobic bacteria tseno di ja oxygen mme seno se fokotse dielo tsa oxygen mo matamong ka bonako le go bakela ditlhapi kgatelelô.
Dielo tsa Ammonia mo Metsing a a Foreshe
Ammonia ke karolo ya nitrogen (N) mo metsing. Ntle fela le fa go na le tseno ka tlhamalalô ya ammonia kgotsa metsi ale mo maêmông a a anoxic thata (a sena oxygen e e lekaneng), bontsi jwa nitrogen mo metsing bo tlile go nna mo sebopegong sa nitrate, e e seng kotsi go tlhapi.
Ammonia e tlhagelela mo sebopegong sa borai (free ammonia) le sa tlhoka-borai (ionised ammonia) fela sebopego sa borai gantsi se kwa tlase ga 10% ya motswako wa ammonia yotlhe. Mo metsing a a bothitho (+20°C) a pH e e kwa godimo (8.5), dielô tsa ammonia e e borai di tlile go oketsega.
Dielô tsa ammonia ka bontsi di ka se bake mathata mo matamong ntle fela le fa a se boteng (5 m kgotsa kwa tlase) ka seêlô sa annual turnover se se kwa tlase ga nngwe. (‘Annual turnover’ ke seêlô se mothama wa metsi o o tletseng o tlaleletswa ke pula kgotsa kelelo-teng ya metsi).
pH ya Metsi a Letamo
pH ya metsi e re bolelela fa letamo le le boesiti kgotsa bo-alkaline thata. pH ya 7 e mo bogareng. Mefuta ka bontsi ya tlhapi ya metsi a a foreshe e kgona go itshokela dielô tsa pH tsa 5 goya go 6.
Selo se se botlhokwa thata se se tlileng go oketsa dielô tsa pH ke kgolô ya bolêlê jo bo nnye. Go tlalatlala ga bolêlê jono go ka oketsa dielô tsa pH segolobogolo mo matamong a mannye a polase, goya go dielô tse di kwa godimo ga pH 9 (segolo thata mo motshegareng). Seno ke ka ntlha ya gotswa ga carbon dioxide ka motsi wa itirelonjo. pH e e kwa godimo eno e tlile go baya tlhapi ka fa tlase ga kgatelelô.
Go fetola/tokafatsa dielô tseno, phetolô ya metsi e a tlhokega, tshela metsi a a foreshe fa go kgonagala. Eseng jalo, tsenya lotlhaka lwa barley.
Translated by Nchema Rapoo