Fish Early Life History: Larval Ontogeny

Question 1

What are the 4 distinct stages of fish development

Answer 1

Embryo, Larva, Juvenile, Adult, Senescent
-Ontogeny
-Reproduction
-Growth

Question 2

The larval period

Answer 2

Considerable developmental change (ontogeny)
Dramatic increase in size (10-1000 times)
Huge mortalities
>99.9% mortality for marine species
>96.4% for freshwater species

Question 3

Challenges of larval phase

Answer 3

Obtaining food (patchily distributed)
Evading predators
Locating and remaining in suitable habitat

Question 4

Advantages of larval phase

Answer 4

Allows dispersal and colonisation of new habitats
Fish can occupy habitats most appropriate to stage of development
- Shallow coastal areas for early life stages vulnerable to predation
- Deeper oceanic waters for adult fish feeding on large mobile prey
Minimises interspecific competition and cannibalism

Question 5

Some adaptations to larval life are:

Answer 5

Transparent bodies : predator avoidance
Elongation of body structures (fins and spines): increases apparent size to deter predators
Soft tissue protrusions (e.g. from gut): thought to perhaps mimic stinging siphonophores or act as lure

Question 6

What are the developmental phases in early life history

Answer 6

Egg development
Hatching
Yolk absorption
Fin development

Question 7

What are demersal eggs

Answer 7

Attached to a substrate or released close to substrate and sink to the bottom
Shallow estuarine and freshwater (e.g., gobies, herring, most freshwater species)
Eggs larger (2-5 mm)
Fewer eggs
Some protection from predators
Larger larvae
Less dispersal

Question 8

What are pelagic eggs

Answer 8

Released in the water column, rarely close to the substrate
estuarine to deep water (e.g., tuna, mackerel, plaice)
eggs small (1-2 mm)
many eggs
high mortality
large dispersal

Question 9

Whats altricial after hatching

Answer 9

Poorly developed Transparent
Small
Low egg yolk
Long larval duration
Many eggs produced
No parental care
eg. Engraulis encrasicolus (European anchovy) 3mm at hatching

Question 10

Whats precocial after hatching

Answer 10

Well developed
Larger at hatching
High egg yolk
Short larval duration
Fewer eggs produced
Often parental care
eg. Hippocampus guttulatus (Seahorse): eggs develop in male brood pouch 10mm at hatching (“birth”)

Question 11

Whats yolk absorption

Answer 11

Altricial larvae still feeding on yolk reserves
Yolk absorption represents the transition from endogenous to exogenous feeding
Once exogenous feeding commences size can increase rapidly
eg. Salmo trutta (trout): yolk sac larva

Question 12

What is sensory develoment important for

Answer 12

Important for orientation, olfaction, settlement & imprinting

Question 12

Example of orientation

Answer 12

First observation of group behaviour in fish larvae
Reef fish Chromis atripectoralis observed prior to settlement onto the reef (Lizard Island Australia)
Showed orientation behaviour in groups (10-12 individuals) but not singly
Groups swam on a 15% straighter course and 7% faster than individuals

Question 12

What happens at fin development

Answer 12

As fins develop swimming abilities improve
Larvae are better equipped to escape from predators and catch food
Generally swimming speedincrease with length

Question 13

examples of other morphological changes

Answer 13

Scale development occurs in late larval life
As larvae develop they lose their transparency and pigmentation develops
Calcareous skeleton becomes ossified
Body proportions change: isometric growth
Development may include dramatic metamorphosis to juvenile form (e.g. flatfish)