Xenopus laevis

Care:

The Xenopus laevis colony ordinarily consists of 10-50 animals.  These are housed at 18.3^oC on a 12/12, light/dark cycle. 

We use carbon-filtered water (mixed bed deionizer, US Filter), to which we add Novaqua (0.5ml/gallon) and NaCl (13.3g/gallon).  The water is stored in large Nalgene carboys.  After the tank is filled, the water is allowed to stand for one day before use. Water in the animals' tank is changed completely twice per week via a static renewal system.

The frogs are kept in clear, polycarbonate tanks measuring 1'6"l x 9"w x 8"h.  The tank covers are made of stainless steel rims to which, neoprene mesh with 1/4" openings is attached.  The lids are secured to the tanks with wire and inspected frequently for holes.  Frogs dessicate rapidly out of water.  A maximum of five adult males or three adult females are housed per tank in 4L of water. 

The frogs are fed every other day with Nasco Frog Brittle (http://www.enasco.com/prod/Static?page=xen_brittle&seqid=4).  They are fed approximately 3-5 pellets per frog or until they are satisfied (as judged by a cessation of feeding).

Of all the colonies, the X. laevis seem the most susceptible to disease.  This is probably due to the fact that, with the high turnover rate, this colony most frequently contains recently shipped animals.  Shipping animals causes stress, which leads to significant immunosuppression and flora or fauna that are present ordinarily may become pathogenic as a result (Tinsley, 1996).  In addition, new animals could introduce novel pathogens into the colony.

Health & Disease:

Aeromonas hydrophila/caviae

Adult male X. laevis with snout lesions caused by Aeromonas infection.

For several months we witnessed the widespread occurrence of dermal ulcers.  Snout lesions, such as the one above, were accompanied by similar lesions on the digits of the forelimbs and less frequently of the hind limbs; the skin appeared to be eaten away, as did the upper phalanges.  In a few severe cases, the nasal septum was visible on the snout.  The symptoms were either present in a nascent form upon arrival from the breeder, or else developed soon thereafter.  Cultures of snout lesion tissue showed heavy growth of Aeromonas hydrophila/caviae. Necropsy of several symptomatic animals showed no obvious internal sign of infection. However, histological evidence indicated considerable liver damage, also due to Aeromonas infection. 

Antibiotic treatment was attempted, administering 4 courses of gentamicin, subcutaneously, at a dose of 2mg/kg.  However, the treated animals fared no better than a control group of equally symptomatic animals from the same frog shipment.  Significantly, all animals lived - the lesions healed, leaving a faint scar. We did not try other antibiotics; possible alternatives are tetracycline or doxycycline. 

Aeromonas hydrophila makes up a normal part of the fauna encountered by Xenopus in their environment and only under immunosuppressive conditions does it become pathogenic.  Aeromonas, along with a host of other gram-negative bacteria, is responsible for Red Leg, a commonly encountered disease plaguing stressed Xenopus colonies.  It is characterized by reddening on the abdomen and inner thighs, caused by vasodilation, and by internal hemorrhaging.  Red Leg has a very high mortality rate if left untreated.

Finally, complete isolation of infected animals was successful in controlling the spread of infection.  New animals were quarantined for a minimum of two weeks: they were housed in separate tanks and kept only on the bottom shelves to prevent water from one tank splashing into tanks with uninfected animals.  When animals were transferred from shipping containers, none of the water or plant material in which they were shipped was transferred with them.  Animals already in the colony are removed to quarantine tanks immediately upon detection of infection. 

Chromomycosis

The first sign of infection appeared immediately following a change of water: a female in a tank of two began expelling blood from her mouth.  Upon closer inspection, we noticed that the extension of the dorso-lateral surface due to the underlying, inflated lung, was missing from the right side and the frog was tilted towards that side.  Necropsy revealed a fully deflated, right lung filled with black/pustulous fluid.  The bottom 3/4 of the left lung was normally air-filled, but it was similarly necrotic at the apex.  The only other sign of infection was a copious amount of recently clotted blood between the surface skin and the muscle layers.  Histological examination of the lungs revealed a chromomycosis infection.  Chromomycosis is an opportunistic fungal infection caused by a variety of pigmented fungi.

Lymphosarcoma

The first symptoms of lymphosarcoma appeared as unusual antero-lateral swellings.  These swellings increased in size.  After approximately a month swellings were also present caudally in the dorsum as discrete lumps.  All swellings were symmetrical, as is typical of lymphosarcoma (the lymph vessels are symmetrically arranged).  Histological evidence supported the anatomical evidence, showing tissue from the lymphatic bumps, as well as from most of the internal organs (ovaries, fat bodies, liver, etc.) to be overrun by lymphocytes of a uniform size and shape. 

Above: dorsal view of lymphatic tumors.  Below: ventral view of same.

In addition, tumorous growths were evident on the hind limbs, both dorsally and ventrally.  The entire lymphatic system was affected, in essence creating a perfect anatomical map of the otherwise difficult to visualize system.

Lymphosarcoma occurs very rarely in Xenopus laevis.  There is some suggestion that it is related to mycobacterial infectious granuloma (Asfari, 1988). However, it is not clear whether the presence of Mycobacterium marinum in such cases is causative or a secondary infection due to weakening of the immune system (Clothier and Balls, 1973). In our case, no Mycobacterium marinum grew in culture.  However, a negative result is not conclusive since mycobacteria are notoriously hard to culture. 

Xenopus tropicalis

Care:

The X. tropicalis colony is housed in the same 1'5"x9"x8" polycarbonate tanks and mesh covers as the X. laevis, in a 26^oC warm room with a 12/12 hr light/dark cycle.  Each tank contains a maximum of 12 animals.  They are fed Zeigler's Salmon Starter Pellets, size #3, twice a week (http://www.zeiglerfeed.com/finfish.asp).  Their water is made up of carbon-filtered water with Novaqua (0.5ml Novaqua/1L water) allowed to stand for 24 hours to release gases and to to warm to warm-room temperature.  The water is changed twice a week, completely, several hours after feeding to allow frogs time to digest. 

The colony consists of 40-70 animals, originally from the Grainger lab http://faculty.virginia.edu/xtropicalis as well as approximately 50 lab bred adults and juveniles. So far, the minimum period from fertilization to sexual maturity has been three months. 

Xenopus tropicalis cap esteria

Care:

This colony was founded with frogs collected by Drs. Kelley and Tobias in Cap Esterias, Gabon in August of 2001. Preliminary analyses indicate a chromosome number of 20 and a call distinct from the X. tropicalis Nigerian colony; 16S ribosomal sequence analysis places this population in the Silurana clade (with the X. tropicalis population from Nigeria).

X. tropicalis cap esterias housing at the Kelley lab.

The colony currently contains approximately fifty wild-collected animals and approximately 300 lab-bred (both in vitro (link to in vitro protocol) and natural) tadpoles and juveniles.  The animals are housed at 26^oC on a 12/12hr, light/dark cycle in 5L or 7L Rubber MaidÔ containers with perforated snap-shut lids; maximum 4 animals per container. 

The X. tropicalis cap esterias are cared for almost exactly like the X. tropicalis nigeria. The water is changed twice a week (carbon-filtered water with 0.5mL/1L Novaqua) using valves (Nalgene 1/2” Barbed Bulkhead Fittings) at the bottom of the containers for drainage in order to minimize disturbance.  They are fed Zeigler #3 Finfish Starter pellets thrice a week.

Health & Disease:

Dermal Infection