Retrofitting fish­ponds amid ex­treme cli­mate change

Agriculture - - Contents - BY ARIEL REPUTOLA

BRACKISHWATER PONDS

In Pam­panga as in most of Cen­tral Lu­zon, tilapia pro­duc­tion shifted from the eastern part where salin­ity and high tem­per­a­ture are a peren­nial is­sue to the west­ern area. Th­ese brackishwater ponds are of­ten wide with a sin­gle pond rang­ing from 3 to 15 hectares and were used for milk­fish and shrimp pro­duc­tion at an ex­ten­sive level. When th­ese were used for tilapia cul­ture, no sig­nif­i­cant mod­i­fi­ca­tions were made. For ex­am­ple, most ponds re­main shal­low which re­sults in higher tem­per­a­ture dur­ing sum­mer.

High tem­per­a­ture means higher rate of evap­o­ra­tion, thus, in­creas­ing the salin­ity and ac­cu­mu­la­tion of de­com­pos­ing or­ganic mat­ter. High salin­ity ponds are al­ways deadly to tilapia es­pe­cially dur­ing stock­ing pe­ri­ods. An­other fac­tor is

the in­ef­fi­cient sup­ply and drainage sys­tem of th­ese very big ponds. Water gets in and out through the same open­ing. Of­ten, the por­tion close to the gate has the best water qual­ity, while about a half or two-thirds of the pond has foul water filled with dead al­gae, fe­ces un­eaten feeds and even dead fish. Need­less to say, this con­di­tion is not con­ducive to growth and sur­vival.

There are prac­ti­cal ways to min­i­mize mor­tal­i­ties and po­ten­tial losses. The fol­low­ing mea­sures are doable and can be done us­ing lo­cally avail­able re­sources:

1. Deepen ponds to a min­i­mum of 1.5 to 2 me­ters. It will make water more sta­ble in terms of tem­per­a­ture, salin­ity, dis­solved oxy­gen and will take longer time for the fish wastes to ac­cu­mu­late and re­sult in neg­a­tive ef­fect on the stock. Although it may be ex­pen­sive in the short term, it is the long term so­lu­tion to mor­tal­i­ties and is best for tilapia busi­ness as the ponds be­come more pro­duc­tive.

2. Pro­vide a sep­a­rate drainage gate op­po­site the sup­ply gate if pos­si­ble. A one-hectare-1.5-me­ter-deep pond should have a gate that can drain 750 cu­bic me­ters per hour so that a maximum of 30% water vol­ume can be changed in one tide cy­cle when water qual­ity out­side is good.

3. If an ad­di­tional drainage gate is not pos­si­ble, in­ter­con­nect two ad­ja­cent ponds by in­stalling two gates along the dike sep­a­rat­ing the two ponds: one in­stalled at one end of the dike and the other at the other end. The dike be­tween serves as a baf­fle. In one of the gates, in­stall a pad­dle wheel, pro­pel­ler or pump to move the pond wa­ters. This has proven very help­ful es­pe­cially when water from the out­side is of poor qual­ity and ad­di­tion of new water is not pos­si­ble. The water gets more oxy­gen while re­leas­ing am­mo­nia and toxic gases dur­ing the process. The de­com­po­si­tion rate of or­ganic mat­ter in­creases with­out com­pet­ing for oxy­gen with the fish stock.

4. Sub­di­vide very large ponds to re­sult in a maximum of 5 to 7 hectares per pond. The smaller the ponds, the eas­ier to man­age water qual­ity. It may en­tail some cost to do, but again, the re­sult can more than com­pen­sate for it.

5. Pro­vide emer­gency aer­a­tors, reser­voir or back up deep­well pumps. While it may be ex­pen­sive, it is an ef­fi­cient mea­sure to man­age water qual­ity when there is no im­me­di­ate source of clean water not only dur­ing grower or fin­isher stages but also dur­ing emer­gency sit­u­a­tions. And again the cost can be eas­ily re­cov­ered in just one har­vest.

6. Con­struct and pro­vide ac­cli­ma­tion ponds with a source of fresh­wa­ter. Smaller ponds must be pro­vided with aer­a­tion sys­tem. This is one of the most crit­i­cal prob­lems in brackishwater ponds that needs to be ad­dressed. Hatcheries are not built to pro­vide fin­ger­lings for sa­line wa­ters. In real prac­tice, the pond owner pro­vides his or her pond’s salin­ity level to the hatch­ery and the lat­ter will ac­cli­mate the fin­ger­lings overnight or in two nights be­fore de­liv­ery. This is an in­ef­fec­tive prac­tice and re­sults in poor sur­vival of only 10 to 50%. Ac­cli­ma­tion should be done slowly at a maximum rate of 0.5-1 ppt per day. This also serves as a mea­sure to avoid pre­da­tion from birds and ex­tra­ne­ous fish dur­ing the fin­ger­ling stage.

FRESH­WA­TER PONDS

Although tilapia cul­ture started out in fresh­wa­ter ponds, many farm­ers are not well in­formed on the prin­ci­ples of pond con­struc­tion. The fol­low­ing are sev­eral things that need to be re­con­fig­ured in or­der to mit­i­gate the risks of ex­treme weather:

1. Deepen ponds to a min­i­mum of 1.5 me­ters. Water tem­per­a­ture is more sta­ble dur­ing hot or cold sea­son in deep ponds. Water de­te­ri­o­ra­tion is also slower as com­pared to shal­low ponds. A depth of one me­ter can no longer be rec­om­mended. Most farms with one me­ter min­i­mum depth suf­fer dur­ing hot or cold months. If a pond owner can man­age to have 2.5 or 3 me­ters depth, this is even bet­ter. Pro­duc­tion per hectare can be higher by up to 66%.

2. Hatcheries are ad­vised to have an av­er­age depth of 1.2 me­ters for breed­ing ponds and not 0.6 me­ters as of­ten rec­om­mended. This is a bet­ter op­tion rather than pro­vid­ing ar­ti­fi­cial shades. Eggs can hardly hatch in shal­low ponds dur­ing hot sea­sons be­cause the breed­ers are too stressed. Dur­ing the cold sea­son, pond tem­per­a­tures quickly go up or down which is again stress­ful to breed­ers. Breeder hold­ing and con­di­tion ponds must be deeper at 1.5 to 2 me­ters. Many hatcheries lose or have de­layed op­er­a­tions be­cause the heart of their op­er­a­tions, which is the breed­ers, all per­ish. It takes 5 to 8 months for new breed­ers to be fully use­ful. Neg­li­gence or lack of knowl­edge is costly to farm­ers.

3. Pro­vide emer­gency aer­a­tors, backup water sources such as deep­wells, reser­voirs, etc. Sev­eral fresh­wa­ter ponds lay par­al­lel to NIA canals. Th­ese canals usu­ally shut down pe­ri­od­i­cally of­ten times dur­ing sum­mer for re­pairs or be­cause there is a water short­age. It is fa­tal when this hap­pens when the ponds are in the grower or fin­isher stages re­quir­ing good water sup­ply. Water qual­ity de­te­ri­o­rates quickly as farm­ers tend not to con­trol feed­ing in or­der to catch up with the tar­get har­vest time or avail of high mar­ket price. As a re­sult, mor­tal­ity oc­curs.

4. Pro­vide nurs­ery ponds.

5. Pro­vide phys­i­cal bar­ri­ers against all ex­tra­ne­ous an­i­mals and preda­tors. Sur­round­ing ponds with net fences has been proven ef­fec­tive against soft-shelled tur­tles that de­vours fishes of all stages. Finer mesh nets can be used as fence if rice­field-eels also oc­cur in the area. Bird scares are rec­om­mended to ward off preda­tory birds. Live­stock must not be al­lowed in ponds as they may bring dis­eases though their fe­ces or saliva. They can also re­sult in de­struc­tion of dikes.

All th­ese rec­om­men­da­tions have been proven ef­fec­tive. Take note that not all mea­sures may be ap­pli­ca­ble to all ar­eas. By fol­low­ing the sug­gested retrofitting of ponds and struc­tures, there is no way a farm could be to­tally lost dur­ing ex­treme weather con­di­tions. Pro­duc­tion can only in­crease - so will prof­its. Farm­ers should al­ways ob­serve suc­cess­ful prac­tices and act based on aqua­cul­ture prin­ci­ple. (TATEH NEWS FEED)

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