What is the Difference Between Skates and Rays

The main difference between skates and rays is that skates are oviparous; laying eggs, whereas rays are viviparous; live-bearing. Furthermore, skates have a prominent dorsal fin while, rays have no or greatly reduced dorsal fin. In addition to these differences, skates have fleshier tails and no spines while rays have whip-like tails possessing one or two stinging spines.  

Skates and rays are two types of dorsoventrally-flattened, cartilaginous fish, belonging to the superorder Batoidea under the subclass Elasmobranchii. Generally, they have cartilaginous skeletons and five or more gill slits on each side of the head. In contrast, bony fish have bony skeletons and a single gill cover.   

Key Areas Covered 

1. Skates
     – Taxonomy, Characteristics, Behavior
2. Rays
     – Taxonomy, Characteristics, Behavior
3. What are the Similarities Between Skates and Rays
     – Outline of Common Features
4. What is the Difference Between Skates and Rays
     – Comparison of Key Differences

Key Terms 

Cartilaginous Fish, Mermaid’s Purse, Oviparous, Rays, Skates, Viviparous

Skates – Taxonomy, Characteristics, Behavior 

Skates are cartilaginous fish that belong to the family Rajidae in the superorder Batoidea of rays. More than 150 species of skates live in the world. The main characteristic feature of skates is mermaid’s purse, which is the egg case in which they produce eggs. Also, the distinct characteristics of the egg case may help to identify different species of skates. Among them, one identifiable characteristic is the keel, a flexible ridge which runs along the outside of the structure. The number of eggs in the egg case is also a characteristic feature. Some may have one embryo, while others can bear up to seven embryos. In addition to these, the fibrous shell around the egg case is also distinguishable as some species have thick layers on the exterior while others do not have this layer. 

Figure 1: Arctic Skate (Amblyraja hyperborea)

Furthermore, the electric organ is the second main characteristic feature of skates. However, both electric rays and skates have this electric organ. Generally, skates have two paired electric organs, which run longitudinally through the tail in the lateral musculature of the notochord. Normally, they produce weak, asynchronous, long-lasting signals. Moreover, this electric organ is a mechanism of defense and hunting. Also, it is a form of communication for reproductive purposes.  

Rays – Taxonomy, Characteristics, Behavior 

Rays are a large group of cartilaginous fish, belonging to the superorder Batoidea. Over 600 species of rays live in oceans while the most identifiable rays are stingrays and electric rays. The main characteristic feature of rays is their dorsoventrally flattened body. They also have a pectoral fin, which extends through the length of the body. Rough skin with placoid scales covers a large portion of the body of rays. Generally, these scales are homologous to teeth with caudally oriented pointed tips.

Figure 2: Rough ray (Raia Rubus)

Moreover, the mouth of rays occurs in the underside of the body, containing euhyostyly, a common jaw suspension to batoids. Also, their gill slits occur in the ventral surface of the body. Besides, the rays have their eyes and spiracles occur on the top of the head; spiracles help to breathe once they bury on the sand.  

Similarities Between Skates and Rays  

• Skates and rays are two types of dorsoventrally-flattened, cartilaginous fish, belonging to the superorder Batoidea under the subclass  Elasmobranchii.  
• They belong to the class Chondrichthyes.  
• Approximately,  there are 630 species of rays and skates on the planet, which are classified into 18 families.    
• They have cartilaginous skeletons, five or more gill slits on each side of the head, jaws, paired fins, and paired nostrils.  
• Their gills are at the bottom while eyes are on the top of the body.    
• Their upper jaw is not fused to the cranium.  
• Moreover,  they have placoid scales as dermal denticles in three layers.  
• The placoid scales are arranged in an irregular pattern in both skates and rays. However, these scales arrange in a regular pattern in sharks.  
• They lack a swim bladder; hence, prefer to live on the bottom of the ocean. Also, their dorsoventrally flattened body is an adaptation to glide in the bottom. They breathe by the spiracles once they are buried on the bottom.  
• They have a good vision even in the dim light and have color vision.  
• Both skates and rays emerged in the  Lower Jurassic (150 million years ago).  
• Usually,  they live in the coastal habitats of the oceans all over the world.  Their mouth occurs underside of the body. Therefore, most of them are benthic while some are pelagic. However, some live in freshwater habitats as well. Usually, skates and rays that are benthic consume shrimps,  crabs, oysters, clams and other invertebrates and others rely on plankton.  
• They swim through the water by gracefully undulating the modified pectoral fins, appearing to fly through the water. Sometimes, they make spectacular leaps from the surface of the water.   
• They are carnivores and may use the senses of smell (chemoreception), vision, hearing, the lateral line system, and electroreception (ampullae of Lorenzini) for capturing prey.  Both can live up to 50 years.  
• Male skates and rays have claspers.  
• Skates and rays are not quality food items for human consumption. However,  they are important in the processing of fish meal as well as laboratory animals.   

Difference Between Skates and Rays 

Definition 

Skates refer to any of the numerous species of large, flat, elasmobranch fishes of the genus raia, having long, slender, tail terminated by a small caudal fin while rays refer to the cartilaginous fish in the superorder Batoidea, consisting of flattened bodies, enlarged pectoral fins fused to the head, and gill slits on the ventral surfaces. 

Taxonomy 

Stakes belong to the family Rajidae in the superorder Batoidea while rays belong to the superorder Batoidea. 

Depth of the Habitat 

While skates are deep water inhabitants, rays are shallow water inhabitants. 

Size 

Moreover, skates are smaller, while rays are much larger. 

Shape 

Skates are triangular or rounded, while rays are diamond-shaped. 

Color 

In addition, skates are typically drab, brownish or greyish in color, while many rays are boldly or colorfully patterned.  

Teeth 

Skates have small, pointed teeth, while rays have plate-like teeth adapted for crushing prey. 

Nose 

Moreover, skates have longer and more pointed noses, while rays have shorter and less pointed noses.  

Dorsal Fin 

Whereas skates have a prominent dorsal fin, rays have no or greatly reduced dorsal fin.  

Lobes in the Pelvic Fin 

Skates have two lobes in the pelvic fin, while rays have one lobe in the pelvic fin.  

Other Fins 

Skates have a caudal fin and first and second dorsal fins, while rays do not have such fins.  

Spines and Tails 

Furthermore, skates have short, fleshier tails and no spines while rays have a long, whip-like tail possessing one or two stinging spines.  

Mode of Reproduction 

Skates are oviparous; laying eggs in rectangular pouches or cases called “mermaid’s purses” while rays are viviparous; live-bearing. 

Mode of Protection 

In addition, skates rely on thorny projections on their backs and tails for protection from predators while rays protect themselves with these stinging spines or barbs.  

Harmfulness 

Skates are harmful while some rays including electric rays and stinging rays are harmful or even deadly to humans. 

Conclusion 

In brief, skates are a type of cartilaginous fish with a triangular or rounded shape. They are small and have a prominent dorsal fin with shorter and fleshier tails and no spines. In addition, they have small, pointed teeth and longer and pointed noses. Most importantly, skates lay eggs. In contrast, rays are a type of cartilaginous fish, including skates. However, they have a diamond-shaped body with no prominent dorsal fin. They also have a longer whip-like tail with one or two stinging spines. Generally, they have plate-like teeth for crushing. Furthermore, rays are live-bearing. Therefore, the main difference between skates and rays is their anatomy and the mode of reproduction. 

References:

1. Albert. “Skate vs. Ray: All You Need to Know.” FishingBooker Blog, 4 July 2019, Available Here.

Image Courtesy:

1. “Amblyraja hyperborea1” By R. Mintern – Report on the deep-sea fishes collected by H.M.S. Challenger during the years 1873-1876 Günther, Albert C. L. G. (Albert Carl Ludwig Gotthilf), 1830-1914 (Public Domain) via Commons Wikimedia  
2. “Rough ray (Raia Rubus) illustration from The Natural History of British Fishes (1802) by Edward Donovan (1768-1837)” By Rawpixel Ltd (CC BY 2.0) via Flickr.