Reproduction in fishes

Question 1

Gonochoristic

Answer 1

dioecious

separate sexes

(all chrondrichthyans, most actinopterygians)

Question 2

Hermaphroditic

Answer 2

normally rare in vertebrates but common in coral reef and deep sea fishes

Synchronous: can be both sexes at the same time - useful in low abundances

Or Sequential: one sec after another
- Protandrous - male becomes female
- Protogynous - female becomes male

Question 3

Reproductive strategies

Answer 3

Most actinopteryginians - large no. of eggs w/ little provision + no aftercare, e.g. cod

Chondrichthyans - few offspring w/ lots of provision + aftercare, e.g. most sharks

Question 4

Cod route…

Answer 4

many fish follow this route

high fecundity - millions of eggs per individual, related to body size (older, larger females produce more eggs)

Question 5

Gametogenesis and vitellogenesis both require…

Answer 5

…large amounts of energy, h/e:
egg t/f = small (<1mm), little yolk

Question 6

Broadcast Spawning

Answer 6

aquatic

high fecundity of small eggs - gametes released into water column for external fertilisation w/o male selection

attrition: far more zygotes produced than will ever reach maturity - mortality rates of over 99.99%

ones better at finding egg will do better = sperm selection

Question 7

Broadcast swimming not random process, h/e…

Answer 7

there are temporal + spatial requirements:
- eggs + larvae usually planktonic so released into offshore currents to take away from land
- strong currents to mix gametes for fertilisation
- synchronisation of timing: availability of food for larvae, greatest chance of fertilisation, predator saturation

Question 8

how do fish spread energy cost

Answer 8

many fish are batch spawners, allowing higher fecundity + reducing risk of mortality caused by freak conditions

Question 9

Synchronisation of spawning

Answer 9

timing ties to maturation cycle within adult which is cued to environment:
photoperiod + temp = most common cues
location important as juvenile stages need appropriate food + protection

Question 10

Spawning sites

Answer 10

if larvae from single spawning site = end up in same nursery

spawning sites = consistent between generations, producing a hydrographic containment of that population

this generates reproductive isolation from other populations of the same spp which spawn at different locations or different times

such independent populations are known as stocksP

Question 11

Parity - how many times do they reproduce?

Answer 11

Semelparity (semelparous)
- once in lifetime (monocyclic)
- usual in stable environment

Iteroparity (iteroparous)
- more than once in lifetime (polycyclic)
- unpredictable environments

Question 12

Parity - at what age or size do fish start reproducing?

Answer 12

age/size at fish maturity

in general, slow growing fish start later in fish

Question 13

Effect of fishing

Answer 13

• fishing removes fish from pop
• with less competition for food, remaining fish grow quicker + mature earlier
• fishing targets older/larger individuals
• selects against later maturing fish, allowing earlier maturing fish (genes) to predominate
• fishing reduces average size/age of first maturity in pop

Question 14

Parental care - 3 strategies

Answer 14

1. Oviparous w/ no parental care
2. Oviparous w/ some parental care
3. Internal incubation/gestation

Question 15

1. Oviparous w/ no parental care

Answer 15

• most common style of reproduction in fish + essential for broadcast spawners
• production of demersal eggs w/o parental care (herring, some capelin) = uncommon + may be the start of evolution to parental care

lay eggs, then leave

Question 16

2. Oviparous w/ some parental care

Answer 16

• spawning site selection
• territorial beh
• nest building
• courtship
• investment activities usually short-lived

Question 17

3. Internal incubation/gestation

Answer 17

• viviparity = rare in teleosts
• more common in elasmobranchs

Question 18

Chondrichthyans

Answer 18

all show mating w/ internal fertilisation

Intromittent organs: claspers formed from the posterior portions of pelvic fins

Question 19

Elasmobranchs reproduction

Answer 19

Oviparity
- few large eggs are laid individually w/ large yolk reserves + tough egg case
- development time = considerable (5-12 months, typically)
- newly hatched juveniles are totally independent

e.g. skates, dogfishes

Question 20

Ovoviviparity

Answer 20

(aplacental)

many elasmobranchs

eggs retained in body after internal fertilisation

if eggs hatch substantially before birth, young will require further nutrition

Uterine oophagy = consuming unfertilised eggs produced for this purpose
Sandtiger sharks show uterine cannibalism = largest foetuses consume smaller ones until only a single pup = present in both of uteruses

some rays produce a fat + protein-rich uterine “milk”

Question 21

True viviparity

Answer 21

(plancetal)
Carcharhiniformes
- developing embryo nourished via placenta
- empty yolk sac attached to the uterine wall to form a yolk-sac placenta - nutrients + O2 pass from mother to foetus through umbilical cord derived from yolk sac stalk, waste passes the other way

e.g. In smoothounds embryo = nourished form yolk sac for 3 months then via plancenta for 7-8 months

Question 22

A special case: intertidal fish

Answer 22

permanent intertidal residents: occupy region most of time

non-resident intertidal visitors: use intertidal on seasonal + tidal basis

Question 23

what conditions do permanent residents show adaptations for?

Answer 23

• wave effects
• temp effects
• desiccation
• respiration in air
• salinity effects

exposed to air - air temp changes more rapidly than water

Question 24

Wave effects

Answer 24

• fish = dense + -vely buoyant (small/no swimbladder)
• some possess suckers (clingfish, lumpsucker, + gobies use modified pelvic fins)
• thickened epidermis
• body shape often depressed to reduce drag + generate downward pressure

Question 25

temp/dessication

Answer 25

• must be eurythermic
• beh adaptation to stay under cover or rockpools
• physiological adaptations such as, slow permeability skin, tolerance to water loss (can be up to 20% of body weight)
• temp + desiccation often control upper limit of distribution

Question 26

salinity/respiration

Answer 26

• can fluctuate from high levels (>90) in rockpools in summer to almost freshwater in winter storms
• intertidal fish need to be euryhaline
• modifications to aerial respiration through modified gills or accessory organs

Question 27

Additional adaptations of intertidal fish

Answer 27

camouflage - morphological coloration is usually mottled brown/green

size - need to hide from predators, minimise wave drag + dislodgement means most are small sized

many intertidal fish show high degree of territoriality

Question 28

what can territoriality divided into?

Answer 28

reproductive & non-reproductive

Question 29

Non-reproductive territoriality

Answer 29

• associated w/ partitioning environment to ensure efficient use of resources (such as food + shelter) + regulating population size
• access to shelter is v important:
  
  • poor swimmers, need holes + crevices to hide in + ability to find them quick when threatened
• aquatic gardening common in tropical blennies, significant energy investment = important to defend them from neighbours

Question 30

Mudskipper

Answer 30

some spp build mud walls to demarcate their territory

Question 31

requirements of territoriality

Answer 31

territoriality = area fidelity + requires:
- fish does not move far (common in intertidal fish)
- ability to recognise + remember surroundings, + use this memory to relocate to territory = homing

• vision + olfaction thought to be important
• hierarchical beh = common
• common blenny show dominance hierarchy which controls their beh patterns

Question 32

definition of homing

Answer 32

to return to a place formerly occupied instead of going to equally probable places

Question 33

Reproductive territoriality

Answer 33

• common in intertidal fish as many show parental care, such as egg guarding
• requires choice of appropriate patch: avoiding desiccation, predation + temp fluctations
• eggs require aerating, defence from predators, prevention of algal overgrowth
• Mudskippers make a burrow nest within their territory. another reason to defend it with walls

Question 34

Biological Rhythms

Answer 34

provide synchronisation of activity within predictably changing conditions of the intertidal

can be initiated by exogenous cues such as:
- flooding
- light
- temp
- salinity

many spp also have endogenous rhythms, which are more important in non-resident intertidal fish

Question 35

Non-resident Intertidal visitors

Answer 35

• most residents = herbivorous but most visitors = carnivorous + have to adjust their beh patterns to coincide w/ presence of their prey
• most visiting fish use the intertidal for many of the same reasons that they use estuaries:
  • predator avoidance
  • increased food supply
  • increased water temp

Question 36

nursery areas

Answer 36

these factors are critical for juvenile fish, so it is common for such areas to act as nursery areas

small fish have:
- bigger range of predators
- smaller range of food items

first year of life is period of maximum mortality, esp the first winter

bigger fish w/ more food reserves survive winter better

adult fish that use such areas do so for the primary reason that they are full of young fish for food