1. Reef Fish Reproduction
Odyssey Expeditions
Reef Fish Reproduction
Odyssey Expeditions – Fish Reproduction

2. Introduction Great diversity in reproduction patterns of fishes
Many change gender
Some mate for life while others are promiscuous
Different strategies have developed in order to reach a common goal - to have the greatest number of young survive to reproduce
The larger the individual the more gametes produced
Odyssey Expeditions
Odyssey Expeditions – Fish Reproduction

3. Reproduction Modes Oviparity - external development
Lay undeveloped eggs
External fertilization (most all bony fishes)
Internal fertilization (some cartilaginous fishes)
Ovoviviparity – internal development
No direct nourishment from mother (fert. eggs carried)
Advanced at birth (some cartilaginous fishes)
Larval birth (few bony fishes)
Viviparity – internal development
Direct maternal nourishment (placental)
Fully advanced at birth (adv. sharks and few bony fish)
Odyssey Expeditions – Fish Reproduction

4. Oviparity Most common Lower energy cost to produce eggs
Survival is low, millions produced in hopes that at least one will survive to reproduce
Larval fishes typically spend 14 – 30 days feeding among the plankton clouds.
Juveniles typically settle in areas far from where they were spawned due to dispersal from the currents
Odyssey Expeditions
Odyssey Expeditions – Fish Reproduction

5. Ovoviviparous/Viviparous
Eggs have lower rate of predation when carried in mother
Much higher energy cost per egg
Therefore fewer eggs produced
Young born as miniature adults
Young generally stay in the same area as mother
Odyssey Expeditions
Odyssey Expeditions – Fish Reproduction

6. Reproductive Strategies
Broadcast spawning
Majority of bony fishes
Release thousands to millions of tiny eggs into water column
Benthic egg laying
Some bony fishes
Tens to thousands of eggs laid in nest
Live-bearing
Few bony fishes
Most cartilaginous fishes
Young emerge from parent free swimming
Few young produced
More parental care = less eggs
Goal is to have maximum number of young reproduce
Odyssey Expeditions – Fish Reproduction

7. Broadcast Spawners Generally occurs at dusk (fewer predators around)
Typically done on an out-flowing tide to get eggs away from predators on the reef
Typically performed at a specific site
May migrate to areas of large congregations (snappers, groupers) or stay on resident reef
Gamete production lowest in energy cost per gamete
NOAA
Migration and Congregation
Odyssey Expeditions – Fish Reproduction

8. Broadcast Spawners
Males and females make an upward dash and release gametes, called spawning rush
Egg and sperm meet in water column
Hundreds to thousands of eggs released in each dash
Higher level of polygamy, but pair spawning common
Spawning Rush
Odyssey Expeditions – Fish Reproduction

9. Broadcast Spawners Fertilized eggs at mercy of currents
Hatch after ~24 hours
Larvae live off yolk after hatching for a short time
Larvae may be spined to reduce predation.
Survival is very low
Theorized that they are able to locate settling habitat by sound and smell
Settle onto reef at night
Larvae with yolk
NOAA
Odyssey Expeditions – Fish Reproduction

10. Benthic Egg Layers Oviparous Typically spawned at daybreak
Fishes generally small in size
High energy cost to males who prepare nests and tends the eggs (remove debris, defend eggs)
Way to ensure he is the only one to fertilize eggs (he hopes)
Female deposits eggs in nest built by male
Males come along periodically and fertilizes them
Nests may have more than one females clutch
Sergeant major tending eggs
Breeding
Odyssey Expeditions – Fish Reproduction

11. Benthic Egg Layers No migration or surface dash risks
Larvae developed after ~7 days and generally begin a planktonic existence for dispersal and feeding.
Male jawfishes and some cardinalfishes keep eggs in mouths.
Male sygnathids (seahorses and pipefishes) brood eggs in a pouch
Jawfish with eggs
Odyssey Expeditions – Fish Reproduction

12. Live-Bearers Very few bony fishes Typically cartilaginous fishes
Viviparous and Ovoviviparous
Fertilization internal
Sperm transferred into cloaca (opening used for excretion and reproduction) by the males claspers (modified pelvic fin)
Internal fertilization
Odyssey Expeditions – Fish Reproduction

13. Live-Bearers Sperm fertilizes few eggs
In hammerhead and requiem families (viviparous) young may be cannibalistic, eating other young and eggs in the womb.
Gestation period of 6 to 22 months.
Birth to live young
Birth of live young
Odyssey Expeditions – Fish Reproduction

14. Breeding Chances Semelparous – spawn once then die
Ex. Lamprey, salmon
Iteroparous – spawn more than once
most fishes
Semelparous salmon
Odyssey Expeditions – Fish Reproduction

15. Mating Systems
Promiscuous – both sexes have multiple partners (mass spawning events, nassau grouper)
Polygamous – one sex has multiple partners
Polygyny – males have multiple partners (most common)
Harem formation – male has breeding right to group of females (wrasses)
Polyandry – females have multiple partners (uncommon)
Monogamous – sexes have one partner (butterflyfishes, anglefishes)
Polygyny Harem
Odyssey Expeditions
Monogamous
Odyssey Expeditions – Fish Reproduction

16. Genders Gonochroistic – sex is fixed, one sex (most fishes)
Hermaphroditic – contain both sex organs at some point
Simultaneous – both sexes at once (deep water fishes, hamlets)
Sequential – changes sex
Protandrous – male into female (moray eels)
Protogynous – female into male (most common)
wrasses, parrotfishes
Jon Buchheim
Odyssey Expeditions – Fish Reproduction

17. Secondary Characteristics
Monomorphic – no visible external differences between sexes (most fishes)
Dimorphic – Visible external differences
Male typically more colorful and ornate
May be permanent or only during spawning
Wrasses, blennies, parrotfishes
Female
NOAA
Male
Odyssey Expeditions – Fish Reproduction

18. Courting Aids in species recognition Pair bonding
Spawning site orientation
Synchronous gamete release
Overcome territorial aggression
May be simple or complex
Change color, make sounds, “dance”
Odyssey Expeditions – Fish Reproduction

19. Alternative Mating Strategies
Satellite males – Mimic female behavior and coloration
Move into nest of male and releases sperm without the immediate attention of the male
Sneaker males – Generally smaller and immature in appearance (may look like females)
remain hidden and then dart through nests or spawning rush and deposit sperm on the fly.
Able to release sperm without guarding male stopping them
Odyssey Expeditions – Fish Reproduction

20. References Buchheim, Jason. Tropical Marine Biology. 1995
Deloach, Ned and Paul Humann. Reef Fish Behavior: Florida Caribbean Bahamas. Florida: New World Publications, Inc., 1999
Helfman, Gene, Bruce Collette, and Douglas Facey. The Diversity of Fishes. Massachusetts: Blackwell Publishers, 1997
Spying on the sex lives of wild fish – Reproduction – Brief Article. June USA Today (Society for the Advancement of Education). 11 Jan
Odyssey Expeditions – Fish Reproduction