Electric Ray Fish

Electric ray fish also known as torpedo fish or electric ray or just torpedo is the genus of ray and belongs to the families of torpedo known as Torpedinidae, Nirkidae, Narcinidae and Hypnidae that are named after their ability to produce electric shock. Usually, the torpado animals are mainly cartilaginous fishes that have a flattened structure with enlarged fins that are the most distinctive characteristic of any fish with bony structure protruding from its body and is covered with membranous skin and are of first-order Torpediniformes.

They are known for generating electric ray shocks that can range between 8 to 220 volts depending on the species of the four families that are broadly divided on the basis of the electric shocks the species of rays are able to produce. They usually do this as their self-defence mechanisms or for stinging the prays. There are about 69 different species belonging to the four families of rays mentioned. 

The electric ray fish or torpedo fish as they are famously known as are normally found in the warm and temperate waters. Crampfish and numbfish are the most popular members of the torpedo genus. Most of the torpedo fish prefers to live in shallow water but few of their species like Benthobatis prefers to live in a depth of the ocean at about 1000 m or 3300 feet. They are mostly slow-moving dwellers at the bottom of the sea bed that feeds on fishes and preys on the invertebrates. They are usually of no or very little commercial interest and are harmless until they are stepped on or touched. In ancient Greece and Rome, the maladies such as headache or gout were treated by using the electric shocks produced by the ray species specially Torpedo Nobiliana.

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Description 

The electric ray fish has a length that varies from about 30 cm that is a foot or less to 2m that is as long as six feet and has a rounded pectoral disc that is joined with non-pointed and non-hooked shaped dorsal fins that are usually large rounded angular in shape running along the lateral side of the electric ray. In genus torpado and ray family members like numbfish that are biologically known as Narcinidae have reduced dorsal fins. 

The first and second dorsal fins originate from the posterior area and end in the pelvis fins. Though their body is mostly flabby and thick they have usually soft and loose skin and possess a strong and stout muscular tail that has well developed and definite structured caudal fins, they are generally smaller than those attached with the circular pectoral disc. They do not possess any fish scales that are biologically termed as dermal pore denticles and thorns that are usually found in other fishes as they grow out of the skin of fish outwards and are a prominent feature of a fish. 

The torpedo fish electric organ is usually situated on both sides of the circular disc and is composed of well-modified muscle tissues. They mostly resemble the shape of a pair of kidneys and are found beneath the dorsal fins of the pectoral disc. The projecting nose and mouth of the ray fish are broad and generally larger in Narcinidae but species of other families have a smaller dimension as compared to the former. 

Generally, the mouth, nostrils and the individual openings of the gills are underneath the disc. The ray fish usually activate the electric torpedo organ for censoring location or defending themselves and hunting down prey. The maximum voltage released by them is good enough to paralyse an adult human. As the electric rays are found mostly in shallow water depth and have a sluggish movement due to their hefty body structure and a large circular disc at the front they generally propel with their tails and do not use their pectoral fins as the other ray species generally do. 

The electric rays are most of the time confused with the Stargazers as they also possess electric shock organs that are located on the dorsal surface of the head. They have a pattern to capture their prey where they usually lie and stand still on a sand bed or other similar substrate and wait for the prey to swim over them when they stung the electricity to capture them easily. The lesser species of electric ray varies at their dorsal area where the colouration of dorsal surface varies from dark brown to light brown and also reddish-orange and have irregular ring patterns on them whereas the ventral surface is usually yellowish to greenish in tone. 

The lesser electric ray can also be distinguished from the other ray family by the length of its stout and preorbital length that is almost 11 to 13% outfits the total length of the body.  The juveniles of the lesser species of rays usually have dark blotches and rings accompanied by dark oval loops on the pectoral disc. Electric rays have 17 to 34 tooth rows in each jaw depending on the species and primarily on the size of the ray fish. They have a sharp cupus and chronicles but the teeth band at the corner of the mouth of the fish falls short in size than the other teeth.  The torpedo fish diagram is provided below for a clear understanding of the ray fish structure.

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The full-grown length of the adult lesser electric ray fish that are found along the coast of Florida is 22 to 23 inches or 559 to 839 mm TL for males and for females it's about 20 to 26 mm or 508 to 660 mm TL. 

Electric Ray Shocks

Electric ray is one of the most electrosensitive animals of all the other animals combined. They have the eyes on the top of the head and beneath the round circular dorsal fin hence resulting in poor vision. Hence, to compensate for the poor vision, the other sensory organ in the electric ray, especially the sense of detecting electricity is a predominant feature. Some of the species of ray and skates that are considered as the outside species of the ray family have their electric organ in the tail but unlike them, the electric torpedo ray has two pair of electric organs on both the sides of the head and is beneath the circular dorsal fins. 

The electricity generated by the organs travels from the lower portion of the body to the upper portion in the case of an electric ray. The electric ray organs are quite visible from the front of the eye to the rare side of the dorsal disc. The pair of electric emitting organs are controlled by four central nerves from each side of the electric lob which also acts as a special brain lobe that is different in colour from the rest of the brain of the electric ray. The main branch then branches itself repeatedly and attaches itself to the lower plates of the batteries that the fish possess which is of multiple hexagonal columns similar to that of a honeycomb structure. Each of the columns in the honeycomb structure comprises a minimum of 140 to a maximum of a billion gelatinous plates. Also, a parallel circuit system runs down to the freshwater batteries placed in series in the marine fish that conduct high voltage electric shocks. The parallel system is embodied as freshwater is not as good a conductor of electricity as that of seawater due to the absence of the salt content in it. The diagrammatic illustration is provided below.

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Reproduction, Food Habit and Distribution

All the species of ray including lesser electric ray have a common ovoviviparous mode of reproduction where the female ray fish holds the embryo in its uterus. The initial nourishment is gained by the embryo through the yolk and then the mother ray releases a special fluid that is secreted from the female ray’s uterine lining that is known as histotroph. The usual gestation period of the lesser electric ray is three months after which the female ray gives birth to 5 to 15 electric rays but there is always a possibility of diapause that is the cessation of the development of the young after fertilization if the conditions are at their optimal level. In that case, it has been observed that the gestation period may delay to 12 to 14 months but further studies need to be done in order to establish this theory. 

The electric ray fishes are very common in the Gulf of Mexico but they usually prefer to be in shallow water where they are buried inside the sand or the sea bed or swim along with the seagrasses. Thus they are most often seen in the coastal waters of the Atlantic Ocean stretching from Argentina to North Carolina. The lesser rays are often found at an ocean depth of 180 feet or 54.86 meters. A much smaller population of the electric ray family has been seen in the Pacific ocean of Yucatan. The lesser ray fish exhibits monogenean infestation in their gills especially when they are held captive for a long time. The biggest predators of these fishes are sharks of the bigger size and large fishes. Electric rays mostly feed on polychaete annelids as their primary feed. But they also pray on small snake eels, small bony fishes, anemones and crustaceans.  

Interaction with Humans

The involvement of the various electric ray species has been witnessed since ancient times. Much earlier in Greece, the doctors used the electric ray fish to paralyse in order to numb the pain of childbirth and operations. A renowned Roman physician named Scribonius Largus documented the use of torpedo fish in treating severe headache and gout in his medical journal named Compositiones Medicea in 46 AD. 

Before the invention of the current or electricity, the people of the primitive era believed that the torpedo ray fishes and their other species are magical creatures and are believed to have supernatural possession because of their ability to paralyse and numb the fisherman without even touching them. This has been documented in historical studies for several centuries. 

There have been more than 60 species that have been identified under the 12 genus of ray that has been broadly divided among two families. For instance, the narcinids belong to the family of Nacradinae. The nature of the torpedine is to feed upon large prays using their sting to provide an electric shock to them and then swallow them as a whole while the narcinids usually target small prays that are either buried under the sand bed of the ocean or under the substrates of the ocean. Studies show that both the species use their electric shock mechanism for defence but it is not clear that narcinids also use it for feeding.    

Fun Facts about Electric Ray

A Few Fun Facts About the Electric Rays are as Follows:-

1. An Australian coffin ray that belongs to the genus Hypnos monopterygius has an enormously big mouth that allows them to swallow the prey that is half the size of their own body.

2. All the living creatures can produce electricity but the rays have two separate organs to generate electricity of high voltage. While the large Atlantic torpedo rays are able to generate as large as 220 volts that is enough to bring down an adult human, smaller rays like lesser electric rays belonging to the genus Narcine Brasiliensis produce very minor electric shocks of about 37 volts.

3. Most of the electric rays have the tendency to bury themselves under the sand bed of the ocean during day time and come out at night. But if any prey encounters the ray during their leisure period of the daytime they stun them with the electric shock and then guide the dead prey to the mouth with the help of pectoral fins as their mouth is located below the part of their body.