How big can a female stingray get


External features

Back side

The eyes are raised on the head and can be pulled in if necessary.
Similar to cat eyes, stingray eyes are very sensitive to light, so that stingrays can see well even in low light.

Placoid scales or skin teeth are the white dots on the right picture. The tips of these scales have a similar structure to teeth, with dentine and tooth enamel. This makes the skin of the rays feel like sandpaper. In some species of rays these scales are greatly elongated on the tail and, as in the picture below, form rows of thorns.


--The Spray hole or spiraculum behind
--the eyes is an additional one
- Breathing opening, especially when the animals
- They can lie on the ground like this
- Breathing water without sand and silt
- suck in.

--The Sting is the weapon of defense
--the stingray. It is made of lime
--and is covered in poisonous tissue.
- A sting falls about every six months
- from and will be replaced by a new one.
- In the picture you can see like him
- next sting under the old sting
- grows up, sometimes it grows
- new but also over the old sting.
- Most have the tail end
- a small freshwater ray
--Caudal fin.



Ventral side


In the entire area of Pectoral fins and the belly rays have sensory organs with which they can perceive prey. One can observe very nicely in the aquarium that the ray reacts immediately as soon as it touches the food with its pectoral fin and transports the prey to its mouth.
They are mainly around the mouth Lorenzini ampoules. These electroreceptors are under the skin, on the outside you can only see tiny pores. With these sensory organs, rays can locate very weak electrical fields, such as those generated by muscles (e.g. the beating heart) of buried prey.
Above that Mouth is the nasal and dental cartilage so that the mouth with the teeth cannot be seen. With the nasal and dental cartilage, the ray feels whether something is edible.
Gill slits there are 5 on each side.
Klasper are the male sexual organs. As with the sharks, two claspers are always formed as extensions of the pelvic fins in the rays. They are already clearly recognizable at birth, so that the sexes can be easily distinguished, but they only reach their full size at the onset of sexual maturity.

Mouth and teeth

The picture shows again in large size the nose and dental cartilage, above the two nostrils and in the open mouth below part of the teeth in the lower jaw.
The tips in the upper area of ​​the mouth are not teeth, but rather skin protrusions of the nose and dental cartilage.


Mouth of a Potamotrygon motoro


Some species of freshwater rays have been found to have longer and more pointed teeth in sexually mature males than in females. It is not yet known whether this difference in dentition is always present or only during the breeding season.

The following picture shows the teeth of a Dasyatis Sabina (Atlantic stingray). This species of ray has created a freshwater population in Florida. There the animal was caught, a large female with a 37 cm disc diameter.
Here you can clearly see how the teeth are arranged; similar to sharks, new ones keep growing and replacing the worn ones.
The denture shown has a width of 73mm; the tooth band in the upper jaw is 37mm wide, in the lower jaw 34.5mm.


Photo: Copyright Jim Bourdon elasmo.com

Internal organs

Freshwater rays are quite large Gills. Since they have a high metabolism, they need a corresponding amount of oxygen. Since the oxygen content is lower near the ground, they have to carry a lot of respiratory water through the gills. In contrast to sharks, in which the gills are automatically perfused while swimming, freshwater rays have to breathe actively. In their natural habitat they like to rest in shallow water, probably because the oxygen content is higher near the surface.

All cartilaginous fish lack the swim bladder to regulate buoyancy. The large oil-containing one forms a certain balance liver. Even so, freshwater rays are unable to float freely in the water. If they do not swim, they will sink to the bottom.

Seen from the ventral side, one finds behind the large liver stomach and Intestines.
The intestine has another peculiarity that is particularly found in sharks and rays, the Spiral fold. This helical structure increases the surface area of ​​the intestine so that the food can be better utilized.
The spiral fold also creates the typical shape of the skate dung, which has a rubbery, twisted structure like a spiral-shaped twisted silicone sausage.

When a ray is really eaten, you can tell by the strong arching of the back and stomach.
In pregnant females, the back also arches on both sides of the base of the tail, as this is where the uterus is located, which visibly enlarges during pregnancy.

Cartilage skeleton

Freshwater rays belong to the class of cartilaginous fish or Chondrichthyes. This group of fish also includes the sharks and chimeras. In these fish, the skeleton consists of cartilage in which calcium is partially embedded.

In the picture you can clearly see the pelvic cartilage where the pelvic fins attach and how the pectoral fins come together at the head end.

Between the head and the attachment of the pectoral fins is the gill space, between the attachment of the pelvic fins and the pelvic cartilage is the abdominal cavity with the internal organs.

The poison sting made of lime can be seen on the tail.

This is a female animal, one would also see the clasps in the male, as these are strengthened by the storage of calcium salts.


A fossil Heliobatis radians
This picture in the original: Charlie's Fossil Fish Market

Embryonic development

The development of the embryos in the womb is very interesting. The freshwater rays of South America are matrotroph viviparous (máter, lat. = Mother; trophé = food; vivus, lat. = Alive; párere, lat. = To give birth).
The embryos hatch from the egg shell in the womb. The embryo is initially supplied by the very large yolk sac in the uterus (uterus). In addition, the embryo is supplied with uterine milk via trophonemata (néma, Greek = thread), villi in the uterus of the female. The embryo absorbs these nutrients and oxygen through fine blood vessels that grow out of the gill slits and mouth. After a gestation period of 3-4 months, the young are born fully developed and only have small remnants of the yolk sac.


P. motoro embryo, back view
Diameter 3.5 cm, length 8 cm
Both photos Y. Miura

Belly side, you can see the blood vessels protruding from the gill slits and the large yolk sac
 

 

"It makes me feel sick when I see myself from the inside!"