FRESH­WA­TER EELS

Usu­ally as­so­ci­ated with co­ral reefs, one species of Mo­ray might sur­prise you by turn­ing up in your lo­cal store’s fresh­wa­ter sec­tion.

Practical Fishkeeping (UK) - - Contents -

Usu­ally as­so­ci­ated with co­ral reefs, one species of Mo­ray might sur­prise you by turn­ing up in your lo­cal store’s fresh­wa­ter sec­tion.

I’VE BEEN for­tu­nate enough in my time as an aquar­ist to have cared for a num­ber of species of mo­ray eel, from the smaller in­ver­te­brate preda­tors through to some mon­strous pis­ci­vores. De­spite their dif­fer­ences, they all shared a com­mon theme – they were all reef-dwelling marine fishes.

When, some years ago, my friend said he’d found some fresh­wa­ter morays for me, he had my at­ten­tion and, a week later, I had two new pets. I was lucky, though, that I had the re­sources to de­ter­mine that this species be­longed in a brack­ish en­vi­ron­ment, not a fresh­wa­ter one.

‘Fresh­wa­ter mo­ray’ is a bit of a mis­nomer, made up of half-truths: yes, this is a real mo­ray eel and yes, it may oc­ca­sion­ally be found in near-fresh­wa­ter en­vi­ron­ments, but Gym­notho­rax tile in­hab­its tur­bid es­tu­ar­ies, river mouths and other brack­ish coastal en­vi­ron­ments where fresh and salt wa­ters min­gle.

Per­haps its other com­mon name of In­dian mud mo­ray is a bet­ter fit. It doesn’t be­long to the In­dian coast­line alone, though, find­ing homes west­wards along the coasts of South­east Asia and through to In­done­sia and the Philip­pines. It re­port­edly oc­curs in Hawaii, too, de­spite the mas­sive ex­panse of deep wa­ters be­tween these places. When Fran­cis Hamil­ton first de­scribed this slimy an­i­mal to the world in 1822, he didn’t wait more than a sen­tence to call this species “an ugly eel”. An un­for­tu­nate in­tro­duc­tion – and quite un­true if you’re bi­ased like I am. Sure, they’re not ‘puffer­fish cute’, but morays have a de­gree of el­e­gance that you’re un­likely to find else­where in this hobby of ours.

Som­bre greens for a back­ground, flecked with small, yel­low­ish-or­ange spots may not live up to the fash­ion show that is the marine mo­ray pa­rade, but as my ad­ven­tures in fresh­wa­ter fish­keep­ing have told me, beauty lies in sub­tlety.

Be­tween the two spec­i­mens that I had kept, there was enough of a dif­fer­ence in pat­tern to dis­tin­guish them from each other: one had larger, more in­ter­spersed or­ange dust­ing, whereas the other was heav­ily

pep­pered with smaller speck­les of the same colour. Given the ex­pan­sive range of this species, some de­gree of vari­a­tion can be ex­pected. Com­pared to its marine cousins, G. tile is dwarfish. While most morays ex­ceed a me­tre in length, G. tile stretches out to 60cm max­i­mum, mak­ing it more suited to most ‘reg­u­lar’ sized home aquaria. This size is achieved fairly quickly.

Life cy­cles ex­plained

At present, the com­plete life cy­cle of G. tile is not fully un­der­stood. In par­tic­u­lar, it’s un­cer­tain whether this species mi­grates out of es­tu­ar­ine en­vi­ron­ments, ei­ther up­stream or out to sea, for breed­ing pur­poses, as may be the case for other low-salin­ity mo­ray eels. The younger stage of these eels (lep­to­cephalus) were in­di­cated (1953; Pan­tulu and Jones) to de­velop within es­tu­ar­ies, and adults were known to travel up­stream as far as the ti­dal limit, in­fer­ring a close re­la­tion­ship with the lim­its of the saline en­vi­ron­ment. It’s known that G. tile is tol­er­ant of fully marine wa­ter, re­flected in the es­tu­ar­ine en­vi­ron­ment it orig­i­nates from – which widely fluc­tu­ates in salin­ity de­pend­ing on the tide – as well as col­lec­tion lo­cal­i­ties from fully marine en­vi­ron­ments. With re­gard to keep­ing

Gym­notho­rax tile in cap­tiv­ity, I would at­tempt long-term main­te­nance in a marine set-up with adult fish only.

How­ever, brief ex­po­sure to saltier wa­ter for younger fishes is not with­out its mer­its, as it’s com­mon prac­tice for fish­keep­ers to use a higher salin­ity as an ex­ter­nal par­a­site treat­ment in place of the com­monly-used cop­per-based med­i­ca­tions, which do not sit too well with this species.

In a mo­ray, you have a liv­ing, breath­ing Hou­dini act as a pet. Ev­ery ef­fort must be made to pre­vent es­cape

Ac­com­plished es­cape artists

Be­ing ben­thic an­i­mals, floor space should be given more con­sid­er­a­tion than other tank mea­sure­ments. Ide­ally, a lone spec­i­men shouldn’t be kept in any­thing smaller than a 120x50x50cm tank, with suit­ably larger ac­com­mo­da­tion pro­vided for mul­ti­ple an­i­mals.

In morays, you have a liv­ing, breath­ing Hou­dini act as a pet. Ev­ery ef­fort must be made to pre­vent es­cape: a tight-fit­ting lid, glass slid­ers, se­cure pipe in­lets and out­lets and even a slightly re­duced wa­ter level can be the dif­fer­ence be­tween a wet pet and a very dry eel on the floor.

G. tile is rarely very ac­tive, spend­ing most of its spare time in a pre­ferred crevice, cave, root or pipe. Pro­vide as much cover as pos­si­ble to en­sure your eels feel com­fort­able. For mul­ti­ple spec­i­mens shar­ing a tank, this is es­sen­tial. G. tile won’t mind shar­ing a cranny with another of its kind, but hav­ing its own re­treat can help ease ten­sions that arise.

Se­cure hard dé­cor well. Ex­plor­ing eels can knock over poorly stacked ar­range­ments. Don’t worry about your mo­ray dis­ap­pear­ing in their hid­ing spaces as they will, in true mo­ray fash­ion, stick their heads out into the open, await­ing pass­ing prey.

G. tile have poor eye­sight and pre­fer a low-light en­vi­ron­ment. If light­ing is too bright, your mo­ray may re­sort to keep­ing to a night-time shift; dim­mer light­ing en­cour­ages day­time ac­tiv­ity and morays will hap­pily feed out in the open in such con­di­tions.

As with other preda­tory fishes, an ef­fi­cient bi­o­log­i­cal fil­ter is a must. A strong flow is not im­por­tant, but good cir­cu­la­tion within the tank can be handy in pre­vent­ing ‘dead’ spots, par­tic­u­larly if a lot of rock­work or dé­cor has been used to cre­ate the plen­ti­ful hid­ing places that this species prefers.

The eel ma­nip­u­lates its body into a knot in or­der to gen­er­ate lever­age on oth­er­wise slip­pery food­stuffs. The head is forced through the knot, with only the food gripped in the mouth be­ing pulled away from the larger food piece

Feed­ing cap­tive morays

Most cap­tive morays read­ily adapt to a frozen food diet and many will hap­pily feed on ‘dead’ foods from the get-go.

If your new pet is hes­i­tant, dan­gling a piece of food in front of its lair, on cot­ton or with rep­tile tongs, and jerk­ing it around as if it were alive may prompt your eel to strike. Use ‘smelly’ foods like oily sar­dine or lance­fish and even­tu­ally, the eels will recog­nise the smell of food in the wa­ter and come to feed with­out your pup­peteer­ing skills.

This species leans to­ward a fishy diet, so should be of­fered a range: sil­ver­sides, lance­fish, sar­dine, hake, or tilapia are com­monly avail­able from seafood shops and su­per­mar­kets. ‘Softer’ in­ver­te­brates are also de­voured with much gusto, and items like bait squid and deshelled prawns and shrimp should be of­fered on oc­ca­sion.

Cut food into bite-sized por­tions. If any­thing is too large to con­sume in a sin­gle bite, your eel might en­gage in ‘knot­ting be­hav­iour’. This is fas­ci­nat­ing to wit­ness, as the eel ma­nip­u­lates its body into a knot in or­der to gen­er­ate lever­age on oth­er­wise slip­pery food­stuffs. The head is forced through the knot, with only the food gripped in the mouth be­ing pulled away from the larger food piece.

Obe­sity can be a prob­lem in cap­tive morays, so in the in­ter­est of your pets’ health, as well as tank wa­ter qual­ity, only feed your eel ev­ery other day or three times a week. Of­fer just enough food to no­tice a slight bulge in the stom­ach (right be­hind the head re­gion).

Other ‘fresh­wa­ter’ species

G. tile is not alone in its ad­ven­tures into less salty wa­ters, as many species of mo­ray find a home in es­tu­ar­ine – and even fresh­wa­ter – en­vi­ron­ments. In the aquar­ium trade, at least three other species pop up in­fre­quently, in­clud­ing the 30cm-long Pink-lipped Mo­ray

(Echidna rhodochilus). This one prefers an in­ver­te­brate-based diet, but can be dif­fi­cult to con­vert from live to frozen foods.

G. polyu­ra­n­odon is also known as the ‘fresh­wa­ter mo­ray’, al­though the name in this case holds a bit more (fresh)wa­ter. Known to oc­cur in a range of salin­i­ties, this species is unique in hav­ing adults spend­ing long pe­ri­ods in fresh­wa­ter habi­tats.

Main­tain Gym­notho­rax tile in wa­ter that can truly be called brack­ish: the low­est end of the range I would rec­om­mend for it would be a spe­cific grav­ity (SG) of ap­prox­i­mately 1.005, near 6.6ppt (parts per thou­sand). This may best suit ju­ve­niles and is a com­fort­able salin­ity to aim for if ad­just­ing fish from a fresh­wa­ter en­vi­ron­ment.

For long-term main­te­nance, how­ever, an SG be­tween 1.010 and 1.015 (be­tween 13 and 20ppt) best re­flects the brack­ish ori­gins of this species. Mild fluc­tu­a­tions be­tween these val­ues do not ap­pear to bother

Gym­notho­rax tile and I proudly grew a duo to a full two feet in adult length un­der these con­di­tions.

Gold mar­bling makes this eel at­trac­tive.

ABOVE: A rare view of a mo­ray out and about.

A divers view: morays are of­ten seen with their head emerg­ing from a dark hole.

The teeth are ob­vi­ous, sharp and back­wards fac­ing, ideal for latch­ing on to prey and fin­gers.

Morays of­ten ex­pose their heads.

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