5" day - Central Institute of Brackishwater Aquaculture

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DO is the mW imp~lnt
ud critical wua purl@ p.rm*er kux of iu
d i i dfe * feed ~onsumFtion MLI marbdirm of m p as wll u indirect
in* * Ma qwlity. DO dwuld bc rminaincd in Ihc ~ lp of 3-10 I&I.
Fa pnrid pnw optimum ccncemtbn of wnsr DO rcpMcd for nuximum
~no~is6ppm.Plo~uponmro~oxypncon~ntuurrb~ fad
carrumpion which kdr to slow grow& md the cuhurc arg~ians become inactive
dhymnuecpi~ktodi91+.Fmrbamar*mrnya~dlorprniuntrm).dic
6mrIukoforpyca. DO&Q~comrrbaam*nrrar: 1.hrrbyproduol
of pbaorynmcdr od 2. Mfbim of umorpbcrlc air. Pbororyntbcrir is Ihr primary
source of W in hckirhwum. hr phaosynthais occw most mpidlv in the ~rf&x
layer of mtcr ud DO conocnmrion klinc wirh depth. in dapr ponds. DO ma:
fill too ppm at depth of I .S m or 2 m. Hence it is dvanugeous to have fairl) shaliow
ponds (75 an to 150 cm deep) for pnm. becam the! dwell mainly cm the tn~nom
ud low DO at the pond bonom would he h f u l
DO Can be i[f~rod by man! factom puricululy wuer tcmpnturc. rcspiruion
of plants and minuls ud the kvcl of oqpaic maim. Ln uupiui wim (h. DO kvel
is n d l y low k.w of hi* tompsnturo. llw conwnmtlon of 10x1s #ubmm
such u unionWrcduced fonn(NH~). sulphur (HIS) d urbon
m*rbolitn(mahlm) increases when low DO level exists Homvcr. In the prerncc
of optimum kvel of oxygen the toxic rubstances uc converted Into their oxidized and
ku h f u l fms. Phytoplanktm mainly blue pun algae In pmds nu) suddenly
die ud dccompac, causing DO drplction. Hutcc, rum formed by phytoplankton
bloom mist be moved pwiodiully in cfder to pavmt DO depletion.
The uses of aerators mull in mixiu of water at surface md bonom md
breakdowns DO nmtification and also can eliminate black mud formed st interface of
pond water and Mom mud. Water cxchangc is thc hest solution to prevent Ion W
problem in the pond nhac aeration is nM practiced. In xrni.intensivc culrurc, rate of
wan exchange depends on the period of culture as indicated belon
lnctnsivc feeding systems require an svcngc exchanyc ralc oi lo4/. per dn)
which un he reduced to 5% in semi-intmsive system. However drilq water cxch~gc
uuully docs not improve wuer quality in bnckirhwuer ponds. bauux mutim water
exchange un discharge carbon, nitrogen and phosphorous substances from pndr
before they un be assimilated. Thus water exchange rater should he reduced In
brack.ishwitn ponds and this should only be uud when necessary
Owr f d i
should be avoided in order to miinuin the DO level One uf the
cflrca of owrhsdlag is to douue cbo fwd wnvarlon eftlclancy. Unuun fwd s.(
decompoDQ rrkulng nuaianu into the w w . Conxgumtly, phytoplmklm
obund.acc iacrru~ u a funaion of increasing feeding re. DO concenvltion
decline more rapidly with depth as phytoplankton abundance increases in response to
higher faatiap ntcs. Besides. the likelihood of phytoplnnklon die-off are greater In
ponds with high feuling rae sad hdanl phgopl.nla0n.