Rivulus Mahdiaensis
Suijker & Collier, 2006
Suijker & Collier, 2006
Background & Natural History;
Recorded collections of Rivulus species from Guyana since 1908 have been few and far between.Consequently, any knowledge of the distribution and diversity of rivulus species from this country is very minimal. Dutch enthusiast Wym Suijker travelled through Guyana six times between 1991 to 2004 to try and catalogue the cyprinodont fauna of the area and search for new and to rediscover old populations of this genus. During his 1995 expedition and along with his wife, he found a new rivulus species in a small creek, within a tributary of the Potaro River, near Mahdia, central Guyana...I can only imagine his joy and excitement as he plucked this piece of gold from that stream.
Images depicting a male and female of the species
(The above images courtesy of Frans Vermeulen at http
/www.itrainsfishes.net)Introduction;
In this hobby of ours we may attend shows and conventions on weekends during the summer months where we indulge in viewing some really spectacular looking species of Killifish and bidding in the auctions for what we would like to have. Sometimes you will come across a certain species in a tank or auction bag that really gets your heart pumping, wishing you could acquire this for your own personal collection. More often than not they go for a pretty penny. This has happened to me only on rare occasions. One such occasion was back in the early eighties with Rivulus xiphidius. (Which I have since managed to acquire and breed successfully). Another such occasion, happened to me much more recently with a little rare killifish species by the name of Rivulus mahdiaensis. I really, really wanted to acquire this beautiful gem, I’d seen so many images of this fish, so I set about trying to locate a breeder, who would let me beg steal or borrow (or maybe even purchase) some initial stock. I knew that this was going to be a tall order as I don’t travel into Europe, so I was going to have to rely on the good old WWW dot for research.
Before anything I needed to find out a little more information on the subject matter, I looked up all the relevant literature I could find on the subject, which in itself is pretty sparse. I managed to glean enough info that would get me started through hobbyists, breeders and technical papers. All I needed now was the fish.
Type Locality - Mahdia The gold-mining town in Guyana (South America)
from which Rivulus mahadiensis receives its name
General;
It was May 2011 when I finally got around to attempting courting certain breeders into parting with some of their prized possessions in order for me to attempt a long term breeding program. Rejection and dejection began to set in, email after email were fired all across the European continent in what seemed a vain effort riddled with blind alleyways. After almost giving up hope, I struck Gold. A breeder in Europe was going to send me some fish....not eggs as what I was realistically only expecting, but actual fish. You can imagine my absolute delight on the hearing of this news. I was on the verge of acquiring this magnificent little fish. The vendor honoured his word and duly dispatched the fish. As with everything there always has to be a glitch, the fish were already in transit when, shock, horror, the aeroplane companies began grounding their planes because of another Icelandic volcano eruption..... Just my bloomin luck....with a little patience, Mother Nature raised a smile and quelled the magma that calmed the volcano and normal service was resumed. The fish arrived safe and well in under a week, three pairs in individual breather bags. On arrival, the water was very cold. I did take some readings for hardness and ph (& TDS) but these were off the scale and couldn’t be relied upon, so followed the lengthy process of acclimatisation. I say lengthy because this was probably the only opportunity I was ever going to get of acquiring this species. If I’d lost them then that would have been that with little or no hope of ever seeing these again.
I placed them all (6 fish) into a large deep sided 3ltr ice cream tub with the water they travelled in. I then set up a drip line from a tank I had previously set up in anticipation of their arrival. The water used was a mixture of Reverse Osmosis, Rainwater & Indian Almond Leaf. This mixture gave me a liquid something akin to what this species would inhabit in the wild (from literature) It was very soft, acidic and was very low in TDS.
I split a large breeding aquarium into three (one pair to each section). I furnished these only with sunken mops, whilst I slowly (over a matter of days) raised the water level. The fish were very timid and stayed within the mops, only venturing out to feed. The females seem bolder than the males at this stage but I expect things will change when they become fully accustomed to their new surroundings.
Juvenile male and female of Rivulus mahdiaensis Blackwater Creek GUY 97/5
(image - male 25mm female slightly smaller)
It took over four days to fully fill the tank that was to be their new home. Originally it was a sparse affair with just a sunken mop as decor. Now the tanks were full (or almost as I like to keep my rivulus tanks a little way short of the brim to minimise losses due to jumping). I proceeded to furnish them the way I intended which was with some Bogwood, Java Moss, Java Fern and Salvinia natans as top cover. I would also include one solitary large floating mop. This mop was double corked at each end, so as no strands hung down but rather the middle would belly into the tank and most of the strands stayed floating or semi submerged. I find I get more spawning activity using this method rather than using the traditional form of floating mop.
The fish were all very timid during their settling in period, They certainly did not like the additional water being added twice a day, even though it was made up correctly so as not to shock them in any way.
This species has a brilliant faking ability, As I added the water they lie in the mops motionless and in the most awkward looking position imaginable, enough into making me think they were keeling over. I knew they couldn’t be as the water was the same chemical makeup and temp as the tank. It was added in small amounts and very ,very slowly, but it still my heart skipped a beat or two watching this, maybe it’s some kind of disguise when threatened.
They even ignored food for a couple of days, just picking at the newly hatched Brine-Shrimp, Monia and Grindalworm that was on offer. I thought I was going to have another finicky timid species on my hands. My fears were unfounded as after the third day all the fish were swimming around with no fear at all; I even had to chase them away from my small siphon tube.
Water Conditions;
From reading various points of literature for this species, I concluded that they needed very soft, acidic water low in Total Dissolved Solids. I make up my water in 10 litre buckets. For my particular area I use 7 parts RO to 3 parts Rainwater. This comes in at around 9 on my Hanna DisT TDS/EC meter but the pH is still fairly high (>6) I reduce this with buffering agent and add some Indian Almond Leaf & Humaquat. All this has an effect on the TDS reading and will shift this up to around 20-25ppm (17.9ppm=1'dKH)This is in or around to what I believe is a good spawning window to get a good viable egg yield.
Other breeders may apply a different methodology for spawning this species, I cannot discount their findings as they may be getting better results than myself, I can only relate my own personal approach when dealing with this species.
Colouration;
As with all the species of killifish that I have been fortunate to keep and breed, describing them in my own words proves to be very difficult and almost always does the species in question a gross injustice.
I will however attempt to give you an insight into their fascinating colouration using text and images on each of the sexes below.
Description of the male of the species;
This is a small rivulin species with males attaining a length of around 40mm. It is distinguishable for most Rivulus species by the profile of its finnage, most notably being the caudal which is lyre-shaped.
Body colouration starts as a dark brown colouration across the back dorsally. The flanks are an iridescent blue with five bright crimson intermittent stripes running laterally from behind the pectoral fins through the body length and into the caudal peduncle. A darker blackish band runs through the eye area and along the flanks just above the belly region. The underside of the fish forward of the anal fin is silver. The snout area has a mustard hue whilst around the eye he possesses a light blue ring with the gill plate being encircled by the same iridescent blue as the flanks. The pectoral fins seem to be clear whilst the ventrals have a subdued yellow tinge to them. The anal and dorsal finnage are very elongated in comparison to other members of the genus, these become even more accentuated as the fish mature. The anal fin is light shimmering blue nearer to the body extending into yellow for over two thirds of its total length. The dorsal is predominately a bright yellow with a mixture of brown blue vertical rays. The Caudal fin is the most striking aspect of this fish and is quite a spectacle. The outer lobes are of a bright golden yellow this is then intersected by iridescent blue which is immediately followed by dark crimson stripes as we move towards its shimmering light blue centre. Again let me re-iterate that this is only a description of the species I see in my breeding aquaria, please refer to the various images both here and the internet for a better perspective on how glorious these little fish look.
(The above image courtesy of Frans Vermeulen at http
/www.itrainsfishes.net)Description of the female of the species;
The female mahdiaensis is slightly smaller than her male counterpart probably in or around the 35mm mark. As with most killifish The female of this species is a pretty drab affair, which is even more accentuated when she is alongside a stunning male. But she is not completely devoid of colour. The predominate hue dorsally and over the flanks is fawn with a series of chocolate coloured vertical splashes saddling the dorsal region. In keeping with the male a dark band of colour emanates from around the eye and runs along the flanks to the caudal. However this band is less distinct than in the male again her belly region is silver. Her eye is ringed with a slight blueish tinge and there is a chocolate colouration to the lower mouth parts. Her finnage as previously mentioned is pretty much unspectacular compared to the male. Her pectorals, pelvics and caudal are for the most part clear with maybe just a slight tinge of red. Her dorsal maintains this slight translucent tinge. The anal fin however possesses the most colouration it starts of with a brownish band and ends with a broad subdued crimson stripe which accounts for 3/4 of the length of her fin. I have not yet witnessed any "rivulus spot" on the female, it may well be pretty indistinct or show up a little later as these fish mature.
Foods and Feeding;
I don't believe that this little rivulus will adapt to eating dried or frozen food, I have to admit I've never tried, opting instead for a cross section of livefoods such as Moina, BBS, Grindal and small Whiteworms. Rivulus mahdiaensis have a very small mouth so I would predominately feed BBS twice daily (in small amounts) and work the other live fodder in and around this regime. With such harsh water conditions BBS, and the worms don't last for too long until they die
I find Moina an excellent food as it stay active under these conditions for a lot longer. Its always a source of amusement watching Rivulus mahdiaensis chase these active crustaceans around their tank.
Mahdiaensis are pretty picky eaters but like to have food around at all times. This seems to help egg production a great deal. I found that having Moina around constantly for the fish to forage on at their leisure was much more beneficial than feeding brineshrimp nauplii twice a day which would only live for a short time frame under these harsh freshwater conditions.
Sex and Breeding;
Rivulus mahdiaensis is a pretty much undemanding little species of killifish providing its specific water requirements are met and good maintenance strategies are adhered to. They like to live in clean water and 10% Bi-daily water changes are one of the keys to success. I keep a pair in a small 15"x8"x6" glass tank complete with an air driven sponge filter. The water statistics are keenly checked and regulated to [ pH 5.4, dKH 1 - Temp 74F ] Once these parameters are met they are what I would term as sporadic spawner's. Collecting 1 - 6 eggs per day is fairly common from a well conditioned adult pair.
Spawning usually takes place in the mops and at all levels, the male will entice the female to a chosen spot in the mop and will wrap his dorsal and anal fins around the female and adopt a characteristic "S" shape then you will notice a sharp jerk, at this point the male will release the female and a single egg will have been deposited within the strands of the mop, it will remain there attached to the mop by a semi adhesive thread, until I harvest it and place it along with others into a small plastic tub.
Eggs and Fry Rearing;
As with most if not all small rivulus species, eggs are laid singly, are very large compared to the size of the female and are few in number.
I personally wouldn't consider the eggs to be overly adhesive, not compared to some other killifish species, so care must be taken when picking them from the mops. The egg size of Rivulus mahdiaensis measures around 1.5mm in diameter and have an amber tinge to the casing.
Rivulus mahdiaensis egg within the fibres of a floating mop
(i) A viable, fertilised egg of the species - (ii) A fertile egg/embryo - (iii) Newly hatched fry of Rivulus mahdiaensis GUY 97/5 Blackwater Creek
[youtube]http/www.youtube.com/watch?v=dWl47kX0HHI[/youtube]
A good meal is always close at hand
/www.youtube.com/watch?v=dWl47kX0HHI[/youtube]A good meal is always close at hand
Summary;
An undeniably stunning representative of the genus. Whilst Rivulus sp. in general once had the stigma of being labelled as "Little Brown Fishes". I invite you all to take a look at this member of the group and I'm sure you'll agree, to a man that, that myth is well and truly dispelled. Rivulus mahdiaensis is a pretty undemanding little fish, providing that all the criteria I have mentioned above are closely adhered to. Most aquarist will tell you that this genre are notorious for "Jumping", whilst this is true to a point, I find if you reduce the water levels in your tanks and provide them with the proper water conditions then this trait can be kept to a minimum. Rivulus species introduced to incorrect or bad water conditions will bolt straight out of the tank. Again I always like to mention that other breeders will have there own methods of dealing with certain species and they may well get better results, I cannot comment on those, I can only submit data of my own personal findings. This article is not meant to be the Holy Grail of how to Keep, Maintain and Re-produce this species, but what it will do is provide a breeder with a platform from which to start. As a Rivulus fancier and in my opinion, it sure don't get better than this, A south American Rivulus that would rival any Africian Aphyosemion for colour.....unheard off.
Breeding Overview;
Tank size: 15"x8"x6"
Decor: Adults - bare tank Bogwood with floating mops, Fry - Java Moss
Water: Very Soft <1dKH (17.9ppm TDS) - pH 5.4 - 6.0
Temperature: 72 - 77 F
Waterchanges: Bi Daily (10%) for breeders and Daily (30%) for fry.
Filtration: Air driven sponge filters set to a trickle.
Feeding: little and often especially fry, remember to syphon off uneaten food.
Lighting: artificial lighting, daylight spectrum tubes on timers.
Notes;
Found close to the mining town in Mahdia, Guyana, this is a very beautiful and much sought after little species. I consider myself very fortunate to have acquired them to my killifish list. I have a great love for these little gems and I am currently constructing a new breeding set-up for this fish alone which should enable me to maintain this beautiful species on a long-term basis.
References/Acknowledgements;
SUIJKER, W. H. (The Netherlands) & COLLIER, G.E. (USA)
Rivulus mahdiaensis, a new killifish from central Guyana (Cyprinodontiformes: Rivulidae)
Zootaxa 1246: 1-13 (29 Jun. 2006)
My gratitude and thanks go to Frans Vermeulen at http
/www.itrainsfishes.net for granting me permission to use his photographs of this species.
