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1 Odyssey Expeditions – Fish Reproduction
Reef Fish Reproduction
2 Odyssey Expeditions – Fish Reproduction
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
3 Odyssey Expeditions – Fish Reproduction
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)
4 Odyssey Expeditions – Fish Reproduction
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
5 Odyssey Expeditions – Fish Reproduction
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 motherOdyssey Expeditions
6 Odyssey Expeditions – Fish Reproduction
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
7 Odyssey Expeditions – Fish Reproduction
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
8 Odyssey Expeditions – Fish Reproduction
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
9 Odyssey Expeditions – Fish Reproduction
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
10 Odyssey Expeditions – Fish Reproduction
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
11 Odyssey Expeditions – Fish Reproduction
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
12 Odyssey Expeditions – Fish Reproduction
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
13 Odyssey Expeditions – Fish Reproduction
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
14 Odyssey Expeditions – Fish Reproduction
Breeding Chances
• Semelparous – spawn once then die– Ex. Lamprey, salmon
• Iteroparous – spawn more than once– most fishes Semelparous salmon
15 Odyssey Expeditions – Fish Reproduction
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)
Odyssey Expeditions
Monogamous
Polygyny Harem
16 Odyssey Expeditions – Fish Reproduction
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
17 Odyssey Expeditions – Fish Reproduction
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
18 Odyssey Expeditions – Fish Reproduction
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”
19 Odyssey Expeditions – Fish Reproduction
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
20 Odyssey Expeditions – Fish Reproduction
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 2002. USA Today (Society for the Advancement of Education). 11 Jan. 2007
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