Fish Reproduction

1
Fish Reproduction

• FNR 351Aquatic Sampling Techniques

2
Objectives

• Understand basic concepts related to several
  reproductive techniques employed in fisheries
  including
• Broodstock management
• Artificial and natural spawning
• Egg stripping
• Egg fertilization
• Egg enumeration
• Egg development
• Egg incubation
• Egg care

3
Broodstock Management

• Definition of Broodstock
• Parent spawners used for the collection of
  gametes (males milt females eggs)
• Acquisition of broodstock
• a) Captive broodstock ________________
• ____________________________________
• b) Wild broodstock Collected in the wild and
  spawned on site or brought back to the facility
  and induced to spawn artificially or allowed to
  spawn naturally

4
Spawning Methods Natural Spawning

• Place the fish in a natural environment (i.e.,
  system that provides the requirements necessary
  for successful spawning) and let spawning occur
  naturally
• Strategies
• a) Nest builders ________________in the bottom
  substrate or vegetation and then _______
  ___________________and/or larvae disperse

Cichlid Nest
5
Spawning Methods Natural Spawning

• Strategies (continued)
• b) Cavity spawners _____________(i.e.,
  _________________________burrow, log, underneath
  a rock)
• c) Mouth brooders Females deposit eggs and the
  ___________________________
• __________________________________ eggs
  carried around in mouth until hatch and larvae
  disperse

6
Spawning Methods Semi-Natural Spawning


7
Spawning Methods Semi-Natural Spawning


8
Spawning Methods Artificial Spawning

• Captive broodstock or wild fish
• Determine gender and estimate ripeness
• Gender may be difficult to determine
• Gametes _________________________(video)
• If not, hold in rearing unit until gametes ripen
  naturally or are induced into being ripe

9
Spawning Methods Artificial Spawning

• Natural approaches ____________and/or
  ____________________manipulation
• Artificial approaches
• Hormone Injections
• Human Chorionic Gonadotropin (HCG) Human
  placental hormone
• Carp Pituitary Extract Contains hormones
  necessary to induce ovulation in fishes,
  regardless of species
•  

10
Spawning Methods Artificial Spawning

• Changes in temperature and photoperiod during out
  of season spawning for ide (Leuciscus idus L.).
  Arrow indicates time of hormonal injection.

www.ejpau.media.pl/.../fisheries/art-05-fig1.jpg
11
Spawning Methods Egg Stripping

• ______________or ______________
• __________________with a clean, dry towel to
  ____________________gametes
• Methods
• a) Hand stripping method
• Hold a female with the vent oriented over a
  collecting pan
• Eggs will flow out freely by gently massaging the
  abdomen from anterior to posterior
• _________________________or will damage the eggs
  and the internal organs of the fish!

12
Spawning Methods Egg Stripping

• Methods (continued)
• b) Air pressure method
• ______________________into the upper abdomen
• Inject air (2-4 psi) to expel the eggs
• Results in less injury to the fish and removal of
  a greater number of eggs
• c) Surgical or sacrificial method
• Anesthetize or sacrifice the fish
• Slit belly from the vent to the gills and eggs
  will flow out freely
• _______________________________________
• ____________________________
•  

13
Spawning Methods Milt Stripping

• Dry off the vent area of a male and hand strip
  milt into a bottle or directly onto the eggs
• First strip away from the eggs to eliminate urine
• _________________________________

14
Spawning Methods Egg Milt Stripping
Using a needle, oxygen is gently injected into
the body cavity of a female trout so that their
eggs are discharged.
Male trout are gently squeezed until they expel
milt into containers of eggs.
15
Spawning Methods Egg Fertilization

• Methods
• a) Dry method
• __________________________
• Eggs and milt are mixed thoroughly
• Sit undisturbed for 5-15 min __________water is
  added
• Why? _______________________________
• ____________________________________
• _____________________________________
• After water is added, let sit for 1min and rinse
  to remove excess milt

16
Spawning Methods Egg Fertilization

• Methods (continued)
• b) Wet method
• Water is added to the pan prior to egg addition
• Must __________________and mix thoroughly in
  order to fertilize eggs
• Let sit for 1 min and rinse

17
Spawning Methods Egg Fertilization

• Methods (continued)
• For both dry and wet methods
• Make sure _____________________________are
  included as could plug the micropyle of the eggs
  and prevent fertilization
• A solution of 0.6 NaCl dissolves protein
• After rinsing the eggs, allow to ________________
• _________________________________________
• Eggs become tougher and the micropyle closes
• Place the eggs into incubating units

18
Spawning Methods Egg Enumeration

• Based on water displacement as a surrogate for
  egg volume
• Add 50 or 100 eggs to a burette containing 25 ml
  of water and read the water displacement
• 3 X and take the average

19
Spawning Methods Egg Enumeration

• Based on the average weight of egg subsamples
• Three 50 or 100 egg subsamples are blotted dry
  and weighed to the nearest 0.01 g
• Average egg weight is calculated and the entire
  sample of eggs is blotted dry and weighed 

20
Spawning Methods Egg Incubation

• Incubation ____________________________________
• Strongly __________________dependent
• DTU daily temperature units __________________
• ____________________________________________
• Based on DTUs, you can estimate very precisely
  when eggs will reach various stages of
  development, hatch, and begin exogenous feeding
• DTUs until hatching range from 75 to 1,200
• Example
• CHS - 750 DTU until hatch and constant
  temperature 50F
• 50 - 32 18 temperature units
• 750/18 42 days
• At 40Fit would take almost twice the time (94
  days) for eggs to hatch

21
Spawning Methods Egg Incubators

• Vertical tray incubators (Heath Trays)
• Eggs placed in hatching trays that are stacked
  vertically
• Water is introduced at one end of the top tray
  and upwells through the tray (screen) bottom,
  thereby circulating through the eggs
• Works its way downward via gravity feed

22
Spawning Methods Egg Incubators

• Hatching jars (McDonald Jars)
• Placed in rows on racks and each with water flow
  at a rate to keep the eggs gently rolling
• Outflow to flush away metabolites
• Screen to prevent escapement of hatching fry or
  outflow to a holding tank

23
Spawning Methods Egg Incubators

• Hatching jars (McDonald Jars)

24
Spawning Methods Egg Incubators

• Hatching baskets
• Baskets are suspended in a flow-trough system
• Need good flow
• Baffles used to circulate water through eggs or
  use paddlewheels

25
Spawning Methods Egg Development
1 min
15 min
50 min
Increase of the size of perch eggs during water
hardening (activation) in water at 14C
26
Spawning Methods Egg Development
Egg Structure Longnose Sucker, Lepisosteus osseus

• Stages 1-5
• Stage 1 showing egg envelopes
• Stage 1 without egg envelopes, showing the dimple
  at the animal pole
• Stage 2, two cells
• Stage 3, four cells
• Stage 4, eight cells
• Stage 5, 16 cells
• j egg jelly
• ch chorion
• ps perivitelline space
• m micropyle
• ap animal pole
• b blastodisc/blastoderm

Long and Ballard. 2001. Develop. Biol. 16
27
Spawning Methods Egg Development
Egg Structure Longnose Sucker, Lepisosteus osseus

• Stages 6-10
• Stage 6, side view
• Stage 6, vegetal pole
• Stage 6, cross-section of the blastoderm
• Stage 7
• Stage 8, smooth-surfaced blastula
• Stage 9, lateral view
• Stage 10, dorsal view.
• vegetal pole
• 1 first cleavage furrow
• 2 second cleavage furrow
• i incomplete blastomere
• c complete blastomere
• y yolk cell
• dl dorsal lip
• ysl yolk syncytial layer

Long and Ballard. 2001. Develop. Biol. 16
28
Spawning Methods Egg Development
Egg Structure Longnose Sucker, Lepisosteus osseus

• Stages 11-15
• Stage 11, lateral view
• Stage 11, dorsal view
• Stage 12, lateral view
• Stage 13, dorsal view
• Stage 14, lateral view
• Stage 15, dorsal view
• dl dorsal lip
• ysl yolk syncytial layer
• es embryonic shield
• ez evacuation zone at the animal pole
• gr germ ring
• ng neural groove
• ypl yolk plug
• nf neural fold
• bp blastopore

Long and Ballard. 2001. Develop. Biol. 16
29
Spawning Methods Egg Development
Egg Structure Longnose Sucker, Lepisosteus osseus

• Stages 21-24
• Stage 21
• Stage 22
• Stage 23
• Stage 24
• ff fin fold
• cl cloacal aperture
• ot otic vesicle
• ol olfactory placode
• op operculum
• ao adhesive organ
• sgc limit of subgerminal cavity
• y yolk sac
• ba branchial arch

Long and Ballard. 2001. Develop. Biol. 16
30
Spawning Methods Egg Development
Egg Structure Channel Catfish, Ictalurus punctatus
31
Spawning Methods Egg Care

• Egg shocking
• Eggs should be physically shocked _______
• ___________________________________
• Tap egg trays or pour into another tray
• Undeveloped or unfertilized eggs remain tender
  and will rupture - water enters the dead eggs and
  coagulates the yolk, turning them white
• Dont shock the eggs too severely or will damage
  good eggs!

32
Spawning Methods Egg Care

• Egg picking
• Remove dead eggs daily ____________
• ________________________________
• Use blunt forceps or a rubber bulb fitted with a
  short length of glass or plastic tubing

33
Spawning Methods Egg Care

• Egg disinfection
• Purpose to prevent the spread of disease,
  especially if the eggs are from another hatchery
• Can do this during the water hardened or eyed egg
  stages
• _______________ (100 ppm for 10 minutes - 2.6 fl
  z of 0.5 Betadine per gallon of water)