Ichthyology
Spring 1999
T. Turner

Lecture 11 Skate and Rays; Sarcopterygii

Recent Revision of Batoid fishes:

McEachran, J.D., K. A. Dunn, and T. Miyake. 1996. Interrelationships of the Batoid fishes (Chondrichthyes: Batoidea). Pp. 63- 84 In M.L.J. Stiassny, L. R. Parenti, and G. D. Johnson, eds. Interrelationships of Fishes. Academic Press. San Diego, CA.

Body form

Pectoral fins fused to head
Ventral gill slits, incurrent respiration through spiracle
Feeding structures: Plate-like dentition, saw-like rostrum, gill structure for plankton feeding
Long whip-like tail with electric organs
Greatly reduced or absent anal fin

Ecology and Life history

Rajidae (Skates) most abundant in deep waters, Dasyatidae (stingrays) most abundant in near and in-shore tropical waters, some freshwater forms; mostly benthic
Mollusk eaters (Rajidae), plankton feeders (Myliobatidae, Mobulidae)
Like sharks, large bodied, slow growing, few/large eggs and young
Direct development
All skates are oviparous
uterine viviparity (Myliobatiformes) -- mother secretes a nutrient rich "milk" which bathes developing embryos; taken up through skin or gut epithelium

Locomotion

Rajiform locomotion - undulation of a wave through the pectoral fin
Eagle rays and Mantas fly through the water by flapping their fins like wings

Taxonomy Following Moyle and Cech, 1996.

Superorder Batoidea (4 orders;13 families; 456 spp. marine and freshwater)

Order Torpediniformes - electric rays,

all piscivorous,
produce electrical currents
body size varies from about 30 cm to 1.7 m in adults ovoviviparous development
Electric organs (derived from muscle) account for 1/6 body weight can produce up to 200V.
Widely distributed Atlantic, Mediterranean, Australia and New Zealand
Family Topedinidae
Family Narcinidae

Order Pristiformes

Family Pristidae - (sawfishes) use saw-like rostrum to slash prey
Long, slim body like a shark, although pectoral fused to head
Can reach lengths of 5 meters,

Order Rajiformes

Family Rhinobatidae (guitarfishes) --
Found in tropical and subtropical seas; can 3 m long
use tail mostly in swimming
Family Rajidae (skates)
Occur in tropical, subtropical, temperate and subarctic waters
Most species-rich family of batoids
Commercial value in many countries -- scallops?

Order Myliobatiformes -

Family Dasyatidae (stingrays)
Whiplike tail with poisonous spine
Distributed in warm shallow waters, world wide
Size range 30 cm - 3 m
Family Myliobatidae (eagle rays)
Large powerful swimmers, wingspan can by up to 3 m
Possess poisonous spines at the base of the tail
Diet consists of mollusks, crustaceans, and fish
Family Mobulidae (manta rays) aka devil rays
Large variation in body size among species: wingspans vary from 1 m to 6 m (about 20 ft.)
Plankton feeders; small fishes
Dangerous when harpooned

Patterns of Diversity (overhead)

Slides of representative taxa

Class Osteichthyes

Subclass Sarcopterygii -- lobe finned fishes

Infraclass Coelacanthimorpha -- a cool coelacanth web page: http://www.dinofish.com

Order Coelacanthiformes (1 family, 1 sp., marine, Indian Ocean)

Family Latimeriidae -- Latimeria chalumnae

Body form

Lobed fins, used for sculling much like lungfishes and ancestral tetrapods
Fish-like heart
Diphycercal tail
Hollow spinous dorsal fin, second dorsal is lobed
Fat-filled swim bladder-- hydrostatic control
Highly electrosensitive, unique series of pits and tubes: rostral organ, similar to ampullae of Lorenzini

Diversity and Distribution

Unknown to science except as fossils (date back to Devonian 121 fossil species described mostly from early Triassic deposits), live coelacanth caught in 1938 off east coast of South Africa, recently discovered in fish markets in Indonesia
Found at depths of 100 to 250 m, 250 - 500m at night

Life history and Ecology

Lecithotropic live-bearer
Rests in the daytime in caves, hunts at night using suction feeding

Infraclass Dipnoi

Order Ceratondontiformes - 1 family, 1 sp., freshwater

Family Ceratodontidae - Australian lungfishes - Neoceratodus

Order Lepidosireniformes - 2 families, 5 sp., freshwater

Family Lepidosirenidae-South American lungfishes (1 sp.) Lepidosiren

Family Protopteridae - African lungfishes (4 sp.) Protopterus

Body form

Possess a mosiac of ancestral and derived traits - complicating taxonomy e.g. Lepidosiren was first described as a reptile:
Paired lungs
Placement of nostrils on near upper lip

Protopterus was first described as an amphibian:
Heart structure (two atria)
External gills as juvenile
All possess massive tooth plates to crush aquatic insects, crustaceans and mollusks
Elongate, about 1 m long, scalation varies
Obligate air-breathers (African and S.A.)
Facultative Air-breather (Australian) undivided lung

Diversity and Distribution

Well known from the fossil record on all major continents (Devonian)
Found only in freshwater; extant forms in South America, Africa, Australia

Life history and Ecology

African lungfish estivation -- construction of a mud and mucus cocoon, fish becomes dormant over dry season (7 to 8 mos. in nature, 4 years in the lab)
Eggs deposited in burrow nests and guarded by the male (African and S.A. lungfishes) young are not obligate air-breathers
(S.A. lungfishes) Male pelvic fins become highly vascularized suggested to supplement oxygen to young, young are not obligate air-breathers
Austalian lungfishes produce 50-100 eggs per spawn, no guarding, direct development

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Updated 02 March 1999, T. Turner