Hammerhead sharks (8 species known) Sea of Cortez has the scalloped hammerhead (Sphryrna lewini) School around seamounts Slow reproductive rate: females mature at 15 yrs, 12 month gestation, 1 year off between pregnancies Fished for food and sport

Why the hammerhead shape? - spreads out sensory ability (electric, olfactory) (disadvantages: prevents jaw protusion & 3D vision) -use the hammer to pin down stingrays and eat them (stingray spines often found in heads)

Figure 8.1

Three groups of fishes Jawless fish (Agnatha) Cartilagenous fish (Chondricthyes) Bony Fish (Osteichthyes) lamprey

Class Osteichthyes (Bony Fish) - Dominant vertebrate in the sea - 26,000 species (96% of all fish, 50% of all vertebrates)

Figure 8.8

Figure 8.14

Sharks (blood = seawater) - concentrate urea - excrete salt in urine, feces, rectal gland How to cope with salt in seawater (tend to lose water) Bony fish (blood<seawater) -kidneys conserve water -excrete salts in urine, feces, gills, skin

Figure 8.16

Figure 8.9 Streamlined (fusiform) Fast-open water Flattened top to bottom - Bottom dweller Flattened side to side- bottom or coral reef Slow - reef Live in vegetation/ coral Trunklike or round - slow moving, reef

Figure 8.13

Maintaining buoyancy Large oily live, light skeleton, pectoral fins for stability Gas-filled swim Bladder, pectoral fins freed for other uses- great diversity of forms

modes of swimming Undulation flex caudal regionmove finstail fin ( eels) (tuna)surgeonfishboxfish

Figure 8.22 Skipjack tuna Tropical species that travels to temperate water to feed. Halfway across globe each year. Salmon Anadromous = Spend lives at sea feeding, return to rivers to breed: Magnetic field and smell of home rivers

Figure 8.22 Conservation threats Polluted rivers, dams Water harvested Introduced species of farmed salmon

Catadromous - breed at sea, migrate into rivers to grow (16 spp freshwater eels) adults spawn and die in Sargasso Sea / larvae in plankton 1 yr+/ metamorphose into juveniles / grow and mature in rivers

Why do fish school?

“selfish herd theory” (middle is safest place to be)

Buoyancy - how to regulate Cartilagenous fish (sharks, rays, chimaeras) -large oily liver, light skeleton - pectoral fins needed for stability/steering Advantages: rapid changes in depth possible Bony fish –Swim bladder (gas-filled sac above intestine) Advantages: freed up pectoral fins for other uses

Strange reproductive practices of fish Hermaphrodites Sex change (born one sex, become the other) Large fish in harems are often sex-change males Large fish in non-harem species are often sex-change females Parasitic males “Sneaker” males that look like females Sex-role reversal (male pregnancy in seahorses) Males often do parental care in fish

Anglerfish adaptations for deep water habitat:

Anglerfish adaptations for deep sea (food and mates scarce) sit and wait predatory behavior bioluminescent lure parasitic males - once males encounter female, they don’t leave

Rainbow wrasse Thalassoma lucasanum Two types of males Two types of reproduction. 1) Females (yellow/red lateral stripes) 2) Primary males (look like females) 3) Terminal males (blueheads) - born female, turn into males

Rainbow wrasse T. lucasanum Two types of reproduction 1)Broadcast spawning Many males and females rush to surface and release gametes 2) Harems: one terminal male guards group of females and mates with them individually. Death of secondary male- large female turns into new terminal male

Mass spawning of the rainbow wrasse Thalassoma lucasanum

Barred serrano Serranus psitticinus Sea of Cortez Simultaneous hermaphrodite (can act as male or female at any time) -dominant male in harem mates with “females”. Serranus annularis Caribbean Orange back basslet

Lecture ended here.

Male pregnancy in seahorses -Placenta - Long-term pair bond -Daily dance of pair

Conservation of Sea Horses 20 million caught each year - 95% chinese medicine - 5% aquarium trade 32 species (threatened status)

Coelocanth (lobe-finned fish)