Breeding of Freshwater Stingrays
In my limited experience, breeding of freshwater stingrays is not nearly as difficult as we have been lead to believe. I want share my experiences to help others breed their rays. I think that it would be amazing to see stingrays undergo the captive breeding efforts and successes that many other pets have seen.
The first and most important step in breeding freshwater stingrays is obtaining a pair of rays that are sexually mature. In my opinion, this is the most difficult step. Most stingrays available to hobbyists are juveniles that are not yet sexually mature. For reasons that are too numerous to list here, many hobbyists are unable to keep their stingrays alive long enough for them to reach maturity.
Physical indications of sexual maturity are absent in female stingrays. It is most often judged by size or age of the animal. Physical maturity in males is best judged by the size of the claspers. At sexual maturity the male stingray’s claspers will enlarge and exhibit a rolled and swollen appearance. Clasper size in relation to disc size of male stingrays often varies greatly. It is not unusual to see small specimens with fully developed claspers and to see large rays with relatively small, undeveloped claspers. Thus, indicating that there are factors other than size that are directly related to sexual maturity. Other generalized reports indicate that male stingray claspers can develop very rapidly in the presence of a sexually mature female. This seems to indicate some sort of hormone trigger.
The amount of time it takes to reach sexual maturity is a debatable topic. It is thought to be influenced by genetics, food intake and possibly pheromone triggers of the opposite sex. One report indicates that a captive pup gave birth to her own litter of pups 18 months after she was born. With an average gestation period of just over three months, this means she was pregnant at roughly 15 months of age. Most female potamotrygon motoros that I am aware of have been at least 12” in disc diameter and approximately three years old at the time of their first litter of pups.
One of the most frequent questions asked on ray websites is, “what is the smallest tank size I can have to keep a pair of stingrays in for life.” That is a difficult question. With superior filtration, and mass water changes the tank could be quite small and for most hobbyists the tanks are small in relation to the size of the fish.
There are many standard size aquariums in the 120 gallon + range that can easily house many species of rays for a very long time. These are readily available at local fish stores and are proven to be cost effective. These costs can be easily driven down with home made stands and filtration systems.
In addition to the standard tanks, there are an abundance of companies on the internet that can make custom glass and acrylic aquariums. These are more expensive than the off the shelf types but they can be configured to fit your fish and your filtration needs. There are even some stackable systems out there that are amazing. There are also some commercially available koi show ponds and livestock troughs that provide the large surface area required to keep rays and are very inexpensive compared to aquariums of comparable size.
When it comes to breeding, enclosure size may or may not make a difference. Conventional wisdom says that bigger is better. However, there are several hobbyists out there that have had opposite experiences. One hobbyist is consistently breeding his pair of potamotrygon motoros in a standard 180 gallon aquarium – 72” x 24” x 24”. By most ray keepers standards this tank is too small to house adult specimens but they are obviously healthy or they would not be breeding. Another breeder says that his potamotrygon magdalenae seem to have more frequent litters when the trio is confined to a smaller tank size.
My rays are breeding in a 400+ gallon pond that is positioned in my basement. The pond is constructed from a sheet of plywood that has been framed with 36” high walls. The walls are lined with plywood and then sheets of insulating foam. A pond liner has been folded inside the large box and the top of the pond was trimmed out with some 2” x 6”s that provide additional stability. I made a lid out of a plastic sheet and some PVC tubing to cut down on evaporation. It is filtered with a large home made wet / dry, a fluidized bed filter and a power filter. I also have some additional power heads that provide water movement. The pond is heated to 82 degrees Fahrenheit by three 300W heaters that are located in the sump of the filter. The Ph of the water is generally right around 7.8. Water changes of 30% are done two to three times per week and the water comes straight from the water softener.
The second hurdle that needs to be cleared in order to breed stingrays is the feeding of the pair, especially the female. I personally do not believe that most people feed their stingrays enough. It is often said that “a healthy stingray never refuses food.” While I think that is an overstatement it has some basis in truth. Stingrays consume a lot of food. You can feed them until they refuse more and their stomachs are bulging as if they are going to burst. Then you can feed them again a few hours later and they will greedily accept the food like they haven’t seen any in day or more.
I believe that the volume of food is critical when it comes to the breeding of stingrays. It has been shown in some species of saltwater stingrays that pregnant females have the ability to absorb the growing pup fetuses back into their bodies if the conditions are not right for her to give birth. Assuming that the same is true for freshwater stingrays, one of the most critical constraints on a pregnant female is need for calories to keep up with the metabolic needs of growing pups.
Backing this theory up are two hobbyists that are regularly breeding freshwater stingrays. They contend that they have correlated a lack of litters with a lack of time to feed the stingrays the frequency that they believe they need to be fed. Both hobbyists also believe that they have had pregnant females terminate pregnancies when personal schedules did not allow the female stingray to be fed for a period of as little as two to three days. This seems to indicate that freshwater stingrays may be able to absorb the pups during times of “hardship.”
Recent studies in Brazil indicate that the stomach contents of most stingray species consist more of invertebrates than any thing else. Stingrays are eating freshwater shrimps and crayfish. They are also eating snails, worms and other bottom dwellers as well as some fish.
My concerns when feeding my stingrays are quality and variety. For most stingray hobbyists a solid portion of the stingrays’ diet consists of commercially prepared frozen foods. In the wild, stingrays do not eat peeled, de-veined, head removed shrimp. They do not eat small fish that are gutted and de-headed like the grocery store smelt. They do not eat chunks of salmon filet and catfish nuggets. They eat crustaceans and fish with all of the organs, bones and skin or exoskeleton included. I often wonder what nutritional deficiencies captive rays have because they miss out on much of the organ meats, bones, etc. and the vitamins, fats and minerals that they provide.
It would be wonderful to be able to recreate the diet that they have in the wild. However, these foods are more difficult or expensive to obtain and with the live foods you always run the risk of parasites. A healthier alternative would be to raise your own feeder; fish, crayfish, snails and earthworms are all very real options.
Once a sexually mature pair of rays is found you need to look for signs of mating behavior. During the “courtship” process, male stingrays will bite at the outside edge of the female stingray’s disc. This biting will generally occur toward the rear half of the female but not always (please keep in mind that this behavior is not unusual in males and possibly females that are not sexually mature….some rays are just bitey).
There are some great pictures and videos on various websites of hobbyists that were lucky enough to get pictures of their stingrays while in the “act.” In my experience, this seems to happen more in the late evening or early morning. I have caught my pair in the “act” on two different occasions in the early morning. Unfortunately, I startled them both times and the activity ceased.
During mating, the male will hold onto the female with his mouth and attempt to turn the female over or position himself so that he is underneath her. This activity generally occurs somewhere in the water column of the tank. It can happen near the bottom but, they are generally swimming through the water during the copulation. If the male is successful in positioning himself or the female, he will insert one of his claspers into her vent (cloaca) and fertilize the female. Which clasper is used depends on which side of the female he has a hold of with his mouth. The copulation itself is short normally lasting less than 30 seconds.
Determining whether of not a female stingray is pregnant is not easy. There are examples on the web of people giving ultrasounds to stingrays that are amazing and accurate. The outlines of the bodies of the pups are clearly visible. Most hobbyists will not have this luxury. However, there are signs. Males often stop their incessant biting of the female’s disc. The female’s appetite can increase dramatically and the rear half of her body begins to enlarge upward. The most definitive sign is movement of the pups in the swollen area of the female’s body. This is only noticeable late in the pregnancy but it is definitive.
My pair of potamotrygon motoro has had six litters of pups. Each time the pups were born between the hours of 11:00 pm and 6:00 am. My personal thought is that this is some sort of defense mechanism for the pups. This may give them time to use their camouflage to avoid natural predators. I am not sure what other hobbyists or aquariums have experienced in regards to the times of births.
Although I have never seen it first hand, I have seen pictures and videos of freshwater stingrays giving birth. The one commonality is that the female does not have her body on the ground during the birthing process. She is either swimming through the water column or has her body up on the side of the aquarium (which makes for great photos). The pups are born rather quickly and other than their colors and patterns they are perfect miniaturized replicas of their parents.
One of the other interesting things about stingray reproduction is that they can become pregnant again almost immediately after the birth of a litter of pups. It is very common for litters of pups to be no more than 100 days apart. The gestation period takes 90+ days. One website shows pictures of an ultrasound performed on a pregnant female stingray in which the outlines of the developing pups can be seen as well as the presence of eggs. While pregnant, the female ray is preparing to become pregnant again.
When pups are first born they do not seem to be skittish or wary of their surroundings. In fact, I have seen newborn pups cruise right over the tops of their parents and up the sides of the aquarium. They look as if they are right at home. At this time, they have a yolk sac from which they obtain their nutrients for the first few days of life. This small yellowish sac is about the size of the end of a Q-tip. Over the next three to even days the pups will absorb the yolk and it’s nutrients until the sac completely disappears and is absorbed by the body.
As soon after birth as possible I recommend removing the pups and placing them in their grow out tank. Although it is rare, there have been reports of larger rays eating or harming young rays. I move the pups within 24 hours of birth. I fill the aquarium with as much of the birthing water as possible and acclimate them in the same manner I would a newly acquired specimen.
I remove the new born pups from the pond with a small acrylic rubber maid container. I corner the pups against a wall and slowly scoop them up. This does not seem to stress them much. They never actually leave the water. This small, clear container gives me a chance to really look the pups over. They can easily be sexed by looking at them through the bottom of the container and they can be easily measured. There has been anywhere between three and six pups per litter. The pups of the larger litters (of five and six) measured in the 3.5” to 4” range for disc diameter and pups of smaller litters (of three and four) measured 4.5” to 4.75” in disc diameter.
At this time I also complete a large water change on the breeding tank. I have found that the water is slightly cloudy after the pups are born. I am sure that this slight clouding of the water is from the birthing fluids of the female stingray. On completion of the water change I immediately feed the stingrays in the pond however, they are usually not interested in food. I have found that none of the rays in the breeding pond show much interest in food for the first three days or so after a litter is born. This is in stark contrast to their behavior just before the birth of the pups when they are eating large amounts of food. I have four mature stingrays in my breeding pond; one 11” male potamotrygon histrix, one 14” female potamotrygon leopoldi, one 14” male potamotrygon motoro (father) and one 16” potamotrygon motoro (mother). It is not uncommon for the four of them to eat almost one pound of smelt in one day’s time prior to the birth of a litter of pups. It is amazing to see that much food go into four fish.
Once the pups have been moved they show the first signs of burying themselves in the substrate, in this case sand. I assume that this is in response to me forcibly extracting them from their birthing home. They spend the bulk of the daylight hours of that first week buried or slightly buried in the sand. They seem to be much more active when the main lights are turned off.
I offer the pups live black worms the day after they are placed in their grow-out tank. Even with the live black worms in the tank (a known stingray delicacy) they do not show much interest. They even seem bothered at times by the moving worms. Some time on day three or four the young rays begin to consume some of the black worms. By the end of their first week of life they are really eating the live black worms and it is evident by their swollen bellies and the spiral shaped globules of ray waste seen in the tank.
The amount of live black worms a group of stingray pups can go through is tough on the pocket book. Although they do not take them for the first few days, I generally offer them these for the first three weeks. At this time I attempt to get them on to commercially prepared frozen foods such as smelt and shrimp. These are the staple foods I feed the other rays. Getting them trained onto these foods is very easy for some rays and a little tougher for others. It is evident that they immediately recognize small pieces of shrimp and smelt as food. All of the pups a visibly excited soon after it enters the water and pounce on it when they find it on the bottom of the tank. However, not all of them actually eat it. I will try small pieces of only these foods for two to three days. If they are not all eating some, I will add small portions of live black worms and lots of pieces of the shrimp and smelt. Within a week or two all of the pups are onto the frozen foods.
The color of the motoro pups is initially very light and washed out. The background color between the spots has not darkened which does not allow the motoro spots to be easily seen. Over the next two months the background color of the pups fills in and the spots and halos become much more defined. During this time the pups generally grow at least one inch in disc diameter. That growth in disc diameter translates to a large increase in body mass.
Appearance & Pattern:
One of the things that has always interested me is how the appearance of the pups is related to the appearance of the parents. My female is a rather drab motoro. She is dark brown with very few spots. My male on the other hand is a striking marbled motoro with too many spots to count. They are at opposite ends of the motoro appearance spectrum. The pups turn out to be almost exactly in the middle. They have a dark brown background with a lot of spots and very little marbling.
I would very much like to have the opportunity to see what the offspring of different combinations of rays would look like. The physical similarities of schroederi to menchacai, leopoldi to henlei and motoro to pearl (just to name a few) can’t help but to bring about questions of relationships between rays and morphological characteristics. This is a very easily debated topic that will have a lot more light shed on it as more and more hobbyists breed their rays.
Stingray breeding is not as difficult as it may seem. To sum it up I would say that there are five steps that you need to take….
1. Obtain a pair of stingrays
2. Give them lots of good foods to eat - both quantity and quality
3. Do lots of water changes – varies greatly for tank size and bio load
4. Let them reach physical maturity – could take several years
5. Leave them alone – nature will take it’s course