Topic 7 Flashcards
List the characteristics of fish eggs
- Egg shape
- Egg size
- Oil globules
- Chorion
- Yolk
- Perivitelline spacewidth
- Embryonic characters
- Miscellaneous characters
What are the miscellaneous characters of fish eggs
- Presence/absence of inner/secondary mbm
- Cleavage pattern
- Size & no. of micropyle
- Biochemical analysis
Egg shape
- Mostly spherical
- Anchovies: ellipsoidal, Gobby: flattened, Demersal species: irregular & large egg mass
Egg size
- Range in size from 0.5 - 26 mm
- Vary with type of breeding strategy –> viviparous: larger eggs
Oil globules
- Presence/absence, no., size, colour, position & pigmentation
- Usually 1 oil globule found posterior to yolk sac (in some species, oil globule can move during embryonic development)
- Can have multiple oil globules –> eventually merge into single globule (as embryo develops)
- identification of demersal eggs (mainly): colour of oil globule
- Presence of melanistic pigment: deep yellow/brown
Purpose of oil globules
- serve to give hydrostatic lift in freshwater eggs
- note: marine eggs maintain buoyancy to a lower energy cost through egg hydration
Chorion
- Highly adapted to the env. conditions under which embryo develops
- Smoothness
- Types of ornamentation: projections, threads, filaments, stalks –> aid in flotation (pelagic) or attachment (demersal)
- Pelagic eggs –> thin chorions in relation to egg diameter; demersal eggs: thicker chorions
- Colour (golden, pink tint)
- Coating can be gelatinous or adhesive
Purpose of chorion
- Attracts & activates spermatozoa for fertilisation
- Prevent polyspermy upon fertilisation (hardening of chorion)
- Protect developing embryo
Yolk
- Degree of yolk segmentation
- Colour (opaqueness)
- Pigmentation
- Circulation pattern –> identify demersal eggs
Perivitelline spacewidth
Most have narrow to medium width perivitelline space
Embryonic characters
- Embryonic pigment in late stages
- Pigment bands
Hippoglossoides dubius (Flathead Flounder)
Egg diameter: 1.5 - 1.7mm Oil globule: many Egg mbm: smooth Property: Pelagic Perivitelline space: wide
Eopsetta grigorjewi (Shotted Halibut)
Egg diameter: 1.0 - 1.1 Oil globule: None Egg mbm: smooth Property: Pelagic Perivitelline space: Narrow
Pleuronichthys cornutus (Ridged-eye flounder)
Egg diameter: 1.1 - 1.2 Oil globule: Single Egg mbm: Sculptured Property: Pelagic Perivitelline space: Narrow
Pleuronectes yokohamae (Marbled flounder)
Egg diameter: 0.8 - 0.9mm Oil globule: None Egg mbn: Smooth Property: Demersal Perivitelline space: narrow
Pelagic vs Demersal eggs
Pelagic eggs: generally thin, homogeneous chorion; yolk is homogeneous, cleave relatively fast.
Demersal eggs: usually thick, more complex chorion which is more resistant to mechanical damage.
How to determine which Zoea stage a mangrove crab is at?
Identification of no. of setae on maxilipeds (modified mouth parts) Zoea 1: 4 setae Zoea 2: 6 setae Zoea 3: 8 setae Zoea 4: 10 setae Zoea 5: 12 setae
If water quality poor (larval mangrove crab)
There is 6 stages of Zoea and in the event of poor water quality, the larval will enter Zoea 6. Zoea 6 has a different morphology
Change in morphology: megalopod
- Body flattened, retracted telson, legs start to grow to the side
- May cannibalise one another so shelter & large SA required to ↓ mortality
Mortality during first larval feeding (mangrove crab)
- Unavailable food source/Inappropriate food source –> spawning earlier than usual
- Newly developed digestive organs + absence of enzymes –> cannot digest
- Size of live feed (not small enough)
Results in starvation & weakened individuals
What happens if a larval crab misses the window period to become next stage?
- Will die within the next few days
- Lack of energy/nutrients –> cannot grow to the next stage
- If remain at one stage for too long, energy required for advanced physiology will be even more & harder to catch up with the ontogenetic changes
General timeline for feeding of larval/juvenile crab
Microalgae: 0 - ∼45 days
Rotifers: 0 - 9 days
Artemia: 7 - 21 days
Seafood paste: 18 - ∼ 45 days
List the environmental factors affecting survival of juveniles
- Light availability
- Photoperiod
- Light intensity
- Aeration
- Dissolved oxygen
- Salinity
- Temperature
- Food availability
Light availability (environmental factors affecting survival of juveniles)
2 protocols
- Lighted environment using rotifers as first feeding & adding microalgae
- Microalgae exists as greenwater (contrast so can see better)
- Concurrent rotifer culture within - “French Technique”
- Rear post larvae in dark env during first few days after hatching
- Feed with live feed as 1st food
Photoperiod (environmental factors affecting survival of juveniles)
- Inverse r/s w water temp –> post-larvae reared at low water temp require longer photoperiod
- Low temp retard growth due to ↓ed metabolism –> need to extend predatory feeding to ↑ larval growth
- 10 - 15 mins of twilight –> prevent stress arising from abrupt switch in light intensity
Light intensity (environmental factors affecting survival of juveniles)
- Differ among species
- Initate predatory behaviour in some fishs (e.g. gilthead seabream)
Aeration (environmental factors affecting survival of juveniles)
- Creates water circulation to suspend post-larve & live feed
- Mix tank water
- Avoid strong aeration during first feeding & development of swim bladder –> result in gas-bubble dz
Dissolved oxygen (environmental factors affecting survival of juveniles)
- provided during water change/aeration
- maintain 80% saturation (may affect physiology if below)
- Addition of microalage –> maintain DO; photosynthesis in light but DO may drop at night time
- Water change at night –> remove catabolites & maintain optimal DO
- Alternative: injection of pure liquid oxygen
Salinity (environmental factors affecting survival of juveniles)
- Change in salinity –> affect metabolism
- Ability to tolerate & overcome salinity differences –> maintain homeostasis
- Osmoregulation –> energetically costly process –> not enough energy to grow
Temperature (environmental factors affecting survival of juveniles)
- ↑ed temp influences rate of metabolism
- Enhanced growth rate in ↑ing temp
- Detrimental effects beyond 40°C –> pejus temp reached: max temp at which max rate of physiological process is observed
Food availability (environmental factors affecting survival of juveniles)
- Maintain high prey density –> stimulate predatory actions + initiate first feeding
- Improve survival possibilities
- Response differ among species (active predators vs less active predators)
- Take into account species’ feeding behaviour, food ingestion & assimilation
Husbandry for mangrove crab
- Water current required –> zoea are planktonic larvae & need to be kept suspended
- Twitching zoea –> may be dying OR undergoing metamorphosis
- Good water quality: 22ppt, Disinfected seawater,, aeration, 50% water change
- Provide shelter to ↓ predatory stress
Problems in hatchery: crab
- Loss of berried eggs on female during incubation (unknown reasons)
- Infestation of endoparasites (biosecurity breach) –> reduced health of female crab & quality of larvae
- Death amidst molting
Sources of risk: Feed
- ↑ in dz occurrence globally –> human activities & climate change
- Pathogens jump hosts/host shift
- Tpt accelerated global movement of species (air tpt)
- brings pathogens & previously unexposed host populations tgt
E.g. By-catch or fish used for fish feed harbour pathogen
- (if frozen) virus contained in thawed water & body fluids of the fish –> released during thawing (if thrown directly in)
- Free virus released in env through live fish & seabird faeces (bird eat sick fish + bird travel long dist –> spread further)
- Virus contained in the tissues of fish consumed by other fish
Source of risk: infected wild stock
- ↑ stocking density –> infections likely to occur
- Pathogen infect wild indivs (interaction, open aquaculture system)
- Infected wild indivs caught & brought back to hatchery/used as feed
- Intrduction of pathogens into hatchery
Source of risk: Malfunction of systems within facility
- UV lights not working –> no chemical filtration
