Reproduction in fishes

Gonochoristic (dioecious)

Separate sexes into female and male

-All chondrichthyans

-Most actinopterygians

Types of hermaphrodism

Synchronous & Sequential

Synchronous hermaphrodism

Can be both sexes at the same time

Sequential hermaphrodism

One sex after another

Types of sequential hermaphrodism

-Protandrous

-Protogynous

Protandrous sequential hermaphrodism

Male becomes female

Protogynous sequential hermaphrodism

Female becomes male

Examples of species that are Protandrous (male to female)

-Amphiprion pacificus (Pacific anemonefish)

-Rhinomuraena quaesita (Ribbon eel)

-Sparus aurata (Gilthead bream)

What are the 2 types of reproductive strategies

Actinopteryginians & Chondrichthyans

Actinopteryginians

Large number of eggs with little provision and no aftercare

Chondrichthyans

Very few offspring with lots of provision and aftercare

Example of actinopteryginians

Cod

Example of chondrichthyans

Most sharks

What do cods have in their reproduction?

High fecundity

-Millions of eggs per individual

What is high fecundity related with?

Body size

-Older

-Larger females produce more eggs

What does gametogenesis and vitellogenesis require?

Large amounts of energy

If an organisms has gametogenesis and vitellogenesis how will be their eggs?

-Small (<1 mm)

-Have little yolk

Broadcast Spawning

High fecundity of small legs-Gametes released into water column for external fertilisation without mate selection

What the problem with broadcast spawning?

Far more zygotes produce d than will reach maturity

-Mortality rates of over 99.99%

Eggs and larvae are usually what in broadcast spawning?

Planktonic

-Released into offshore currents to take away from land

Benefit of batch spawners?

-Allows higher fecundity

-Reduces the risk of mortality

What are the most common cues for spawning?

Photoperiod and Temperature

If a larvae comes from a single spawning site will they end up in the same nursery area?

Yes

Stocks

Independent populations, with reproductive isolation from other populations of the same species

What are the different types of how many times they reproduce?

-Semelparity

-Iteroparity

Semelparity

Once in a lifetime (monocyclic)

-Stable enviroment

Iteroparity

More than once in a lifetime (polycyclic)

-Unpredictable enviroments

What age fish stat reproducing?

First maturity

Effects of fishing

-Removes fish from population

-Less competition for food (Remainder fish frow quickly)

-Fishing targets older/larger individuals

-Selects against later maturing fish (allows earlier maturing fish to predominate)

-Reduces average size/age of first maturity in populations

What are the 3 strategies for parental care?

-Oviparous with no parental care

-Oviparous with some parental care

-Internal incubation/Gestation

Example of a species that are oviparous with no parental care

Herring & some capelin

Features of oviparous with some parental care

-Spawning site selection

-Territorial behaviour

-Nest building

-Courtship

-Investment activities usually short-lived

What is viviparity most common in what type of organisms?

Elasmobranchs

Chondrichthyans

Mating with internal fertilisation

What are the intromittent organs in chondrichthyans?

Claspers

-Formed from the posterior portions of pelvic fins

Oviparity in elasmobranchs

Few large eggs are laid individually with large yolk reserves and tough egg case

-Development time (5-12 months)

-hatched juveniles are independent

Examples of oviparous elasmobranchs

Skates & Dogfishes

Ovoviviparity in elasmobranchs

Eggs retained in body after internal fertilisation

Viviparity in elasmobranchs

Developing embryo is nourished via placenta

-Empty yolk sac attached to the uterine wall to form a yolk-sac placenta

-Nutrients and oxygen pass from mother to foetus through an umbilical cord derived from the yolk sac stalk

What are the challenges of intertidal enviroments?

-Wave effect

-Temperature effects

-Desiccation

-Respiration in air

-Salinity effects

What are the adaptations of permanent intertidal fish for wave effect?

-Dense and negatively buoyant (small or no swim bladder)

-Possess suckers

-Thickened epidermis

-Body shape often depressed to reduce drag and generate downward pressure

What are the adaptations of permanent intertidal fish for temperature/dessication?

-Eurythermic

-Behavioural adaptations

>Stay under cover or rockpools

-Physiological adaptations

>Slow permeability skin

>Tolerance to water loss

What are the adaptations of permanent intertidal fish for salinity/respiration?

-Euryhaline

-Modifications to aerial through modified gills or accessory organs

Additional adaptations of permanent intertidal fish?

Camouflage

-Brown/green

Size

-Small

Territorial

How can territoriality be divide into?

Reproductive and Non-reproductive

What is non-reproductive territoriality associated with?

-Portioning environment to ensure efficient use of resources and regulating population size

-Access to shelter (Poor swimmers)

-Aquatic gardening

What is the most common species that does aquatic gardening in intertidal environments?

Tropical blennies

What does territoriality require?

-Fish does not move far away

-Homing

-Vision and olfaction though to be important

Homing

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

What is reproductive territoriality associated with?

Parental care (egg guarding)

What does reproductive territoriality require?

-Choice of appropriate patch

-Eggs require aerating, defence from predators, prevention of algal overgrowth

What are the exogenous cues from biological rhythms?

-Flooding

-Light

-Temperature

-Salinity

What are endogenous rhythms most important to?

Non-resident intertidal fish

What are the reasons why non-residential intertidal fish use estuaries?

-Predator avoidance

-Increased food supply

-increased water temperature

What did Whitney et al, (2021) investigate?

This study examines how surface slicks—coastal convergence zones—serve as nursery habitats for diverse marine larvae, including over 100 species of commercially and ecologically important fishes.

Key points of Whitney et al, (2021)

High Larval Density in Surface Slicks

-Surface slicks contain 39% of neustonic larval fishes, 26% of zooplankton (prey), and 75% of floating organic debris (shelter).

-Larval fish densities in slicks are 2–110 times higher than in surrounding waters.

Selective Habitat Use

-Late-larval fishes actively select slick habitats due to high prey concentration and shelter.

-These zones significantly enhance larval survival and recruitment into adult populations.

Role in Marine Ecosystem Connectivity

-Surface slicks contribute to coral reef, epipelagic, and deep-water fish population replenishment.

-They help maintain oceanic biodiversity and productivity.

Ecological and Conservation Implications

-Understanding how slicks function can inform fisheries management and marine conservation.

-Protecting these high-density larval zones can support the sustainability of marine ecosystems.