Reproductive strategies in fish

1. Prepared by: Zeinab Klaab

2. Reproductive strategies are structural, functional and
behavioural adaptations that improve the chances
offertilization and/or increase the survival rate
Fish are the most versatile organisms in reproductive
strategies/mechanisms.

3. Semelparity and iteroparity are two classes of possible
reproductive strategies available to fish.
Semelparity
R-selected species Iteroparity
K-selected species

4. More than one spawning during a lifetime
Most fishes use this strategy
K-selected species
grow slowly, reproduce late, produce fewer young,
longer life expectancy, lower reproductive effort (spread
across time), may provide parental care
Stable, predictable habitats – survival to following year is
high
Lower fecundity, but spread out to ensure some
reproduction
~25-60% of somatic energy used for reproduction
Iteroparity

5. Spawn once and die.
Diadromous or highly migratory fishes tend to be
semelparous (salmon, lamprey).
R-selected species
 grow fast, reproduce early, produce many young,
shorter life expectancy, high reproductive effort (“big
bang”), no parental care
Unstable/unpredictable environments – high mortality
Place eggs and young in ideal growing conditions
Overwhelm predators
~60-85% somatic energy used for reproduction
Semelparity

7. 1- Live-Bearing
ViviparousOvoviviparous
Unborn young receive nourishment
from mothers tissues.
 Primary Way: The walls of the egg
follicle are in intimate contact with
the embryo, supplying it with
nourishment.
Eggs hatch within the mother
First Type: The embryo develops in
the egg while the egg is still within its
follicular covering within the ovary,
and ovulation (or release of the egg)
and birth occur at the same time
Second Type: The eggs are released
from the protective follicles into the
cavity of thehollow ovary, where
development continues .
e.g. Hammerhead Sharke.g. Nurse Shark

8. Mouth-BroodingOviparous
 A large number of fish species
incubate fertilized eggs in their
mouths or gills until they hatch.
Then the frys will continue to use
their parents mouth or gills until
they are grown
Simplest form: Females will scatter
their eggs in a water column and males
will eject their “Milt” at the same time.
Some species of fish take greater care
in egg laying locations however and
will return to their place of birth to lay
their eggs.
 Certain species have adapted their
eggs to have a sticky outer coating so
that they adhere to rocks instead of free
floating in the water column
e.g. Tilapiae.g. Betta Fish
2- Egg-Laying

11. External
• Most fishes
• Less time and energy spent in courtship
• Increase number of potential mates
• higher fecundity – more offspring produced
Internal
• Few groups of fishes
• e.g. Chondrichthyes, guppies, mollies
• Requires lengthy Intromittent organ – transfer sperm to females
(claspers, modified anal fin)

12. 1- Monogamy
2-Promiscuous
3-Polygamy

13. 1- Monogamy :
-Monogamy is a mating system where partners live
and exclusively mate with only each other.
-Very rare in the fish world.
-Extend for several years or even a lifetime
- e.g. butterflyfishes.

14. 2-Promiscuous
-Promiscuous is a mating system where both sexes
have multiple partners during the breeding system.
- In fishes, this is the most common mating system.
- No obvious mate choice (both spawn with multiple
partners).
- e.g. Nassau grouper.

15. 3-Polygamy
-Polygamous is a mating system in which an
individual of one sex has multiple partners during
the breeding system.
-Increased chance of passing on “good genes” from
individuals
-under This mating system there are two types:
Polyandry.
Polygyny.

16. Polyandry – one female, several
males.
• Relatively uncommon.
• e.g. Gar fish.
Polygyny – one male, multiple
females.
• Most common.
• e.g. Bluehead Wrasse.
3-Polygamy

17. 1- Simultaneous
2-Sequential
3-Parthenogenetic

18. 1. Gender Systems – in most fishes the sex of an individual is
determined at early stage and fixed; some fishes are
hermaphrodites and can function as males and/or females.
Simultaneous – capable of releasing viable eggs
and sperm during same spawning
fish with ♂ and ♀ gonads
Some can self-fertilize (Rivulus); likely adaptation to lower
population size, isolated habitats
Alternate sex roles during spawning (Serranus); male with harem of
hermaphrodite females :
male removed, largest hermaphrodite female changes into male

19. 2. Gender Systems – some fishes are hermaphrodites and can
function as males and/or females
A- Sequential – function as one sex for part of their life, then switch
Protogynous (protogyny) – start female, change to male; more
common. (first ♀, then ♂)
Protandrous (protandry) – start male, change to female; less common.
(first ♂, then ♀)
B- Parthenogenetic – alternative to traditional gender roles (Unisexuality)
#All female but require sperm from other species to activate cell
division in eggs (genetic info from males is not conserved)
#Produce daughters genetically identical to mother (Poeciliidae )

20. Nutrition of the
Female:
• The feeding condition of the mother can have an important effect on
the final maturation of the eggs.
• The ovary had been unable to obtain the needed amino acids from
maternal tissue when the nutrition of the female had been inadequate.
physiological
factors
(hormones):
• Hormones govern migration and timing of reproduction and
morphological changes
• The pituitary stimulates gonads to producing steroids, which in turn
control yolk formation and spawning.
Ecological
factors:
• Some ecological factors important to spawning are temperature,
photoperiod, tides, water depth, substrate type, salinity, and exposure.

21. • Fishes often spawn at one depth but live at different depths
during other times of the year.
Water
depth:
• Some species will shift spawning sites because of salinity
changes.
• Various degrees of mixing, precipitation, and freshwater
runoff may alter spawning habits.
Salinity:
• A clear example is the black prickleback (Xiphister
atropurpureus), where spawning is shifted from winter in
protected areas to spring in exposed areas
Exposure and
temperature:
Some Ecological Factor