Download Lecture 3 Characteristics if marine fish species File

J S Valeta 2013
Characteristics of marine fish
 Life history
 Marine culture species
Marine fish culture
In the past marine fish were raised
mainly from wild juveniles (e.g. Eels,
milkfish, yellowtail, shrimp farming)
 Hatchery production-improved
technology
 Recent breakthroughs make marine fish
culture a promising field
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Candidates for aquaculture
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The best candidates for aquaculture should:
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1. grow fast
2. grow efficiently (Low FCR)
3. survive well despite stress of captivity
4. have sufficient seed should be readily available
Candidates for aquaculture

Sufficient seed can be made readily available
through;
 Reliable methods for obtaining eggs (broodstock and
hatchery management)
 Maintain suitable environment
 Ensuring good nutrition (feed quality and feeding
regime)
 Control diseases

Methods to achieve these differ among species
Bottleneck

The most common bottleneck in marine
fish culture is low survival of larvae to
the juvenile stage
 Halibut, Hippoglossus hippoglossus; up to
95% mortality because of malformed larvae
Mortalities among juveniles not high.
 This is why mariculture for many species
relies on wild caught juveniles (e.g.
Eels)

Characteristics of Marine fish
Need to know and understand life-history
 High diversity of life history strategies in
marine fish;
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 Can differ in a species between environments
 Can change under domestication

Life history strategy is a result of evolution
and will maximize survival of offspring's in
the natural environment
Life history can consist
of maximum 5 stages
Embryonic stage
1.
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Until exogenous feeding
Larval stage
2.
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Until metamorphosis
Juvenile stage
3.
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Until first reproduction
Adult stage
4.
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Until last reproduction
Senescent stage
5.
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Death
E.K. Balon
Basic life history traits

Age and size at maturation (Broodstock)
 At maturation growth rate is reduced
 In general, fecundity increases with female size

Total investiment in reproduction
 Depends on the overall strategy
○ Semelparous – spawn once in their life, high investment is
expected
○ Interoparous – Spawning repeatedly during their life, investiment
in single reproductive event depends on chance of survival to the
next spawning.

Investiment in individual progeny relates to:
 Egg size
 Parental care
Reproduction

Viviparous
 Fish bear few live young that are very advanced
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Ovoviviparous
 Fish retain the eggs (internally) until hatched.
Larvae are less developed compared to
viviparous species and planktonic larvae are
more common

Oviparous
 Release small to large number of eggs that are
fertilized externally
 This is the most common strategy among fish
Fertilized fish egg
Eggs

Nature of eggs differs between species
 Planktonic; Floating in the water column
 Demersal; sinking, usually larger than
planktonic eggs

Some eggs are sticky and are spawned
to a preferred substrate where they
attach
 E.g African catfish, Clarius Geriepinus
The stickiness of the eggs is brought about
by the adhesive disk on the egg
Parental care

A few marine fish species devote
considerable effort to parental care
 Guarding, fanning, carrying eggs
Parental care
 Parental care is more commonly seen in fresh
water fish
 Parental care can be subdivided into three:
1) No parental care
○ Egg dispersal, planktonic eggs
○ Common in many marine species
2) Low level parental care
○ Gravel nest made but embryos left unattended
○ Common in Salmo spp.
3) High level parental care
○ Common in mouthbrooders e.g. Oreochromis
spp.
Mouth Brooding Tilapia
http://aquatic.org/
Mouthbrooding movie 1
Mouthbrooding movie 2
Number of offspring and survival

No. of offspring and survival inversely related
and depend on species’ life history strategy
Species
Surf perch
Turbot
Number of eggs
(pr. batch)
50
12.000.000
Ocean sunfish
300.000.000
 How many offspring's would each fish have on
average surviving until adult stage if the
population size is not changing?
Survival

Many marine fish produce large numbers
(thousands to millions) of single planktonic
eggs that hatch into relatively weak larvae
compared to freshwater fish

Larvae from drifting eggs undergo wider
dispersal than those from stationary eggs
and the high number can help reducing the
impact of predation
Survival

K-selected vs. r-selected
 K-selected, small number of eggs, low mortality;
Stable and predictable environment
 r-selected, large number of eggs, high mortality in
the natural environment. Unstable and less
predictable environment
Implications for aquaculture

In some species (r), individual female
produces large number of eggs, providing
the opportunity for humans to produce
large number of fish to stock or eat.
 In this case a small brood stock can be sufficient
to provide seed for the production

In other species (K), each female
contributes small number of eggs, so more
spawners are needed
 Larger (more) brood stock is needed compared
to r-selected
Implications for aquaculture
Keeping r-type larvae alive and making them
grow is usually much harder than for
the k-type
Development
Eggs of most finfish desirable for marine culture
are small (0.6-2.0mm diameter) and planktonic
 Among different species, egg diameter and
incubation time are inversely related to
temperature but directly related to each other

 Larger eggs, longer incubation period
 Higher temperatures, shorter incubation period
 Egg diameter tends to be relatively larger at low
temperatures
Larval stage
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From planktonic eggs: Small, delicate,
require live food for 3-5 weeks (zooplankton,
rotifers)
At hatching, most marine species are in the
length range 1-5 mm total length.
Many are fragile and cannot see, swim well
or catch food for 1-7 days
Eyes usually become pigmented just before
first feeding
In larvae that hatch at a small size, gas
exchange occurs through the skin for a while,
 But within few weeks after hatching, functional gill
filaments would have formed
Critical periods
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Fertilization
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Quality of gametes
Temperature and salinity
Correct timing
Handling
At hatching
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Strength of embryo
Suitable temperature
Hatching enzymes
Toxic free environment
Suitable light intensity and photoperiod
Critical periods
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At first feeding
 Strength and development of larvae
 Suitable size, availability and distribution of food
 Suitable light intensity and photoperiod
 Timing
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At yolk exhaustion
 Suitable temperature
 Suitable size, availability and distribution of food
 Sufficient uptake of nutrients from exogenous
source
Critical periods cont.
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At gas bladder filling
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Strength of larvae
Light not too intense
Suitable circulation
Lack of surface film
At change in diet
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Digestive capability
Suitable size, availability and distribution of food
Correct timing
Adequate transition period
Critical periods cont.
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At transition to gill gas exchange
 Overall health of larvae
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At transformation/metamorphosis
 Although less vulnerable to physical injury
(e.g. Protected by fins and scales) juvenile
fish in the wild can be more conspicuous to
predators than the larvae, which are partly
transparent
Growth

Size hierarchy can occur because of
 genetic difference in growth rate,
 competition for food, social dominance,
 lack of predation on small fish
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Abnormal fish that would be lost to
predation in the wild can survive in
culture
Cannibalism
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Catfish CD
Growth rate

The simplest measure of growth is the
absolute growth rate (AGR):
 AGR=(BW2-BW1)/days
 BW1=body weight at beginning, BW2 at the end
However, fish growth rate is not linear so
AGR cannot predict intermediate weight
 Most commonly used measure of fish growth
is specific growth rate (SGR).
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 more accurate in predicting the intermediate
weights compared to AGR.
 SGR=(ln BW2 - ln BW1)/days
Wild vs. Hatchery fish
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Hatchery reared fish often are different
from wild ones, particularly in:
 shape,
 colour,
 fitness.
Reared fish tend to be shorter and fatter
 Number of factors contribute to this
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 Feeding rate
 Aquaculture environment
Wild vs. Hatchery fish
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Crowding
 Density of fish larvae in culture is much higher than in
the wild (typically 1000 times)
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Different environment
 Tank walls, pipes, aeration, photoperiod, phytoplankton
density
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Different food
 In nature the larvae are exposed to wide variety of
zooplankton, but in culture the diet usually consists of
homogeneous zooplankton, e.g. rotifers and Artemia
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More food
 The food is more abundant in the culture system
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Metabolic and toxic substances
 Ammonia, urea & CO2 – Plastic, metals, chemicals
Aquaculture environment and the
life history of fish
It has been reported for many fish
species that their life history changes
when transfered to culture
 Typically they mature at early age, e.g:
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 Atlantic cod, Gadus morhua
 Arctic charr, Salvelinus alpinus
 Many tilapia species e.g Oroechromis
shiranus