AQUABASICS Which fish don’t need oxy­gen? by An­gel L. Ampil

Animal Scene - - CONTENTS - Text by AN­GEL L. AMPIL

Of course, the an­swer to this ques­tion is sim­ply, NONE. As with all liv­ing things, grade school science has taught us that all fish need oxy­gen to live. This is a fact that all of us as grade school­ers knew a long time ago.

Why then would Filipino fish­keep­ers— who most likely are adult men, who most likely have grad­u­ated from well-re­spected uni­ver­si­ties—even think about ask­ing this ques­tion in fish groups? These fish­keep­ers who fre­quent fish groups are sup­pos­edly the earn­ing group. They are the work­ing class of our so­ci­ety. They are the tax­pay­ers. Yet con­sid­er­ing our coun­try de­pends on this so­cial class for our progress, how can they even think of a ques­tion like this?

Call it lack of anal­y­sis or im­prop­erly rephras­ing a ques­tion, but this ques­tion has been gain­ing no­to­ri­ety among fish groups that it brings about ten­sion among the page view­ers. “Anong isda ang hindi kailan­gan ng oxy­gen?” (What fish doesn’t need oxy­gen?) is gain­ing pop­u­lar­ity lately around fish groups for the wrong rea­sons, spew­ing ridicule and caus­ing cy­ber bul­ly­ing to some ex­tent.

Ir­ra­tional as the ques­tion may sound, there may be a slight point to this ques­tion. An­a­lyz­ing the Pi­noy fish­keeper’s psy­che, the ques­tion should more cor­rectly be stated as “Anong isda ang hindi kailan­gan ng aer­a­tion?” (What

fish doesn’t re­quire aer­a­tion?) If this is the case, then some sem­blance of ra­tio­nal­ity may be de­rived from this ques­tion. If this is in­deed the true ques­tion that the in­quis­i­tive fish­keep­ers mean, then there are some fishes that may sur­vive in tanks with­out aer­a­tion. These fishes thrive in waters with low lev­els of dis­solved oxy­gen. De­pend­ing on the species, these fishes have found their own ways of cop­ing with such an en­vi­ron­ment.

The fish that im­me­di­ately comes to mind is the Fight­ing Fish (Betta splen­dens). Everyone who has kept Fight­ing Fish has kept them in small bot­tles with­out any aer­a­tion. In fact, that’s how we were taught to keep these lit­tle fish, and with good rea­sons. The Fight­ing Fish is a small fish that lives in shal­low stag­nant waters in South­east Asia. They be­long to the or­der An­a­ban­tiformes where some of the fishes are known as “labyrinth fish” that pos­sess a labyrinth or­gan, a struc­ture in the fish’s head which al­lows them to breathe at­mo­spheric oxy­gen. Thus, a Fight­ing Fish can eas­ily sur­vive a small tank with no aer­a­tion at all be­cause of its abil­ity to breathe at­mo­spheric oxy­gen.

Aside from the Fight­ing Fish and other species from the genus Betta, other fishes from the or­der An­a­ban­tiformes that can breathe at­mo­spheric oxy­gen are the Gouramis, Snake­heads, Par­adise fishes, Climb­ing Perches, and Asian Leaf Fishes among oth­ers. There­fore, be­cause of the labyrinth or­gan of these fishes, they are able to live in aquar­i­ums, tanks or ponds that do not have aer­a­tion.

An­other set of fishes that can live in waters with low dis­solved oxy­gen and should do quite well in tanks with­out aer­a­tion are those we fondly call the prim­i­tive fishes. While these are fishes with com­plete set of gills, some mem­bers from this group of fishes have the abil­ity to gulp air us­ing their spe­cial­ized swim blad­ders which act like lungs. And speak­ing about lungs, the best ex­am­ple for this are the Lung­fishes.

Lung­fishes are fresh­wa­ter fishes be­long­ing to the sub­class Dip­noi. To­day there are only six known species of lung­fish, rep­re­sented by 4 African species be­long­ing to the genus Pro­topterus; the lone South Amer­i­can lung­fish, Lepi­dosiren para­doxa; and the very rare Queens­land

lung­fish, Neo­cer­a­to­dus forsteri, which is en­demic to Aus­tralia.

Lung­fishes are very hardy and can breathe air; they can in fact even live out of wa­ter. In their nat­u­ral habi­tat, African Lung­fishes sur­vive the harsh droughts by bur­row­ing them­selves in mud, form a co­coon us­ing their own mu­cus and es­ti­vate (a pro­longed state of tor­por or dor­mancy) to sur­vive the long dry sea­son. They are known to sur­vive up to 4 years while un­der­go­ing es­ti­va­tion or un­til the rains ar­rive. Once the rainy sea­son floods the co­coon, they break free and con­tinue to live un­der­wa­ter as most fish do.

An­other set of prim­i­tive fishes that are known to gulp air are the Gars. Filipino fish­keep­ers are quite fa­mil­iar with Gars be­cause we have a few species avail­able that are quite af­ford­able to the av­er­age fish­keeper. Gars are from the fam­ily Lepisostei­dae and rep­re­sented by the gen­era Atrac­tos­teus and Lepisos­teus. These preda­tory fishes can be kept in in tanks with­out aer­a­tion be­cause they are able to breathe at­mo­spheric oxy­gen when the wa­ter is low in dis­solved oxy­gen.

The tank, how­ever, should be big as these are huge fishes. I re­mem­ber be­ing awestruck at a sight of a cou­ple of 8 to 10 foot Al­li­ga­tor Gars (Atrac­tos­teus spat­ula) in the 320,000-gal­lon tank in Sea­world San Diego. Well that was Sea­world, we don’t ex­pect to have a tank even just one per of

that at home; but you should agree that the tank will be quite large to ac­com­mo­date such large Gars.

An­other fish Filipino fish­keep­ers may be fa­mil­iar with are the Bichirs from the genus Polypterus and its closely re­lated kin the Rope­fish or Reed­fish (Er­peto­ichthys cal­abar­i­cus), the only mem­ber of the genus Er­peto­ichthys. These elon­gate fishes with mul­ti­ple dor­sal fin­lets pos­sess a pair of spe­cial­ized “lungs” in ad­di­tion to gills, al­low­ing it to sur­vive in very oxy­gen-poor wa­ter. The Bichirs, which are more com­monly called Dar­gon­fins in the Philip­pines, are quite avail­able in the coun­try nowa­days. In fact, all 15 known and de­scribed species should be avail­able in lo­cal fish stores through­out the ar­chi­pel­ago and in spe­cial­ized fish stores.

The world’s largest fish, the Ara­paima, is also an an­cient fish with abil­ity to breathe air. This huge fish is may be placed in a pond with­out aer­a­tion. But it has to be a large pond be­cause it is a very large fish. While the Arowana is closely re­lated to the Ara­paima and is also able to gulp air, I am not aware of any­one keep­ing the Arowana in a tank with­out aer­a­tion. Maybe be­cause Arowanas are ex­pen­sive fishes, fish­keep­ers do not risk their Arowanas in a tank de­void of aer­a­tion. This ac­tu­ally takes me to my main point in this ar­ti­cle. While yes, there are fishes that would sur­vive in oxy­gen-poor wa­ter, aer­a­tion is not the only

thing you need in a tank. In fact aer­a­tion is im­por­tant but is only a small fac­tor in proper fish­keep­ing. More im­por­tantly you will need good, clean wa­ter to keep your fish alive and healthy. And the only way to achieve this is through proper fil­tra­tion and ad­e­quate main­te­nance; which by the way in­creases the lev­els of dis­solved oxy­gen in your tank, mak­ing for a more suc­cess­ful aquar­ium.

We achieve aer­a­tion by hav­ing wa­ter move­ment break the sur­face ten­sion in our tank. The move­ment at the sur­face causes the ex­change of gases thereby mix­ing oxy­gen with the wa­ter. There­fore, the more vig­or­ous the move­ment of wa­ter at the sur­face the more oxy­gen is dis­solved or mixed with wa­ter. An air pump that in­fuses bub­bles in the aquar­ium does not oxy­genate the wa­ter. If you look closely, bub­bles are re­leased by the air­stone and the bub­bles float to the sur­face and burst and are re­leased to the at­mos­phere. The bub­bles do not mix with wa­ter. But the burst­ing of the bub­bles vi­o­lently breaks the sur­face ten­sion and al­lows oxy­gen to mix with wa­ter.

This is the same with fil­ters. All fil­ters work by mov­ing wa­ter through the fil­ter me­dia and re­turn­ing pro­cessed wa­ter in the tank. Through­out the fil­ter sys­tem wa­ter is dis­placed. This move­ment causes the break­ing of the wa­ter ten­sion and en­ables the oxy­gena­tion of the wa­ter.

If you are to prac­tice proper fish­keep­ing, pro­vide your tank with the best pos­si­ble fil­ter and aer­a­tion. While fishes dis­cussed above may sur­vive tanks that are low in dis­solved oxy­gen, they pros­per bet­ter and are health­ier in clean and highly oxy­genated tanks.

Let us avoid risk­ing our fishes in tanks with­out aer­a­tion, no mat­ter what kind of fish you keep. Com­mit to giv­ing the best tank and cor­re­spond­ing fil­tra­tion sys­tem to your fishes. As re­spon­si­ble fish­keep­ers, let us en­sure to keep our fishes alive and healthy. We are the guardians, cus­to­di­ans and care­tak­ers of the­ses fishes and they rely to us for their very sur­vival. Don’t go around try­ing ways to avoid re­spon­si­bil­i­ties of proper fish­keep­ing.

If you can’t com­mit to the re­quire­ments of the fish­keep­ing hobby, there are al­ways other hob­bies more suit­able for you. A fish has a life, let us not take their lives for granted. Let us give them the aquar­ium they truly de­serve. Don’t bother ask­ing ‘What fish does not need oxy­gen?’ be­cause they all do!

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