Growth heterogeneity in predatory fish larvae

Biotic and abiotic influences

Larvi’ 01Gent, 3-6 September 2001

Contributors

P. Kestemont, M. Houbart & A. Cuvier-Péres,University of Namur, Belgium

E. Baras & C. Mélard, University of Liège, Belgium

S. Jourdan & P. Fontaine, University of Nancy, France

M. Paspatis & M. Kentouri, Institute of Marine Biologyof Crete, Greece

Project funded by EC (FAIR 96-1572)

Occurrence of size variation• Multimodal size distributions are present in both populations and cohorts of animals and terrestrial plants

• Size heterogeneity and growth depensation are very common features in fish, particularly in recently domesticated species

Species name Larvalweight (mg)

Initial CVweight(%)

Salmo salar 69.5 7.5Oncorhynchus mykiss 55.7 7.5Acipenser baeri 18.3 8.1Dicentrarchus labrax 0.5 20Perca fluviatilis 0.8 15-20Perca flavescens 0.5 8-10Clarias gariepinus 1.6 9.2Heterobranchus longifilis 2 12.3Cyprinus carpio 1.2 10Carassius auratus 1.1 9Brycon moorei 1.5 11Oreochromis niloticus 10.7 11

Body weight variation of larvae at hatching

Consequences of size variation in larviculture

• Reduced efficiency of the feeding schedule

• Increased agonistic behaviour and competition for food

• Ultimately, emergence of cannibalism or significant increase of its impact on population dynamics in predatory species

Type I cannibalism

seabass

Type II cannibalism

perch

Factors involved in size variation

Interaction of 4 primary factors

1. initial size distribution2. distribution of growth rates resulting from differences among individuals3. size and time dependence of each individual’s growth rate (interaction of the life history pattern with the environment)

4. mortality affecting size classes differently

• different combinations of the primary factors might produce similar final size distributions• a variety of biotic and abiotic mechanisms may affect each ofthese factors in a manner that produces the same result

Interaction of initial size distribution and growth-rate distributionModified from Huston & DeAngelis, Am. Nat., 1987

Assuming that : - a simple growth model (Wt = Wo ert) is applicable- mortality rate = 0 (regardless of size class)

SIZE CLASS

GROWTH RATE CLASSNU

MB

ER P

ER

CLA

SS

(1) (2) (3)

NU

MB

ER P

ER C

LASS

SIZE CLASS

(a)

(b)

(c)

t = 2t = 4

Biological mechanisms producing size variation among larvae

All mechanisms can be classified as :• Inherent : mechanisms with a strong genetic component,expressed to some degree under any environmental conditions

• Imposed : mechanisms that require certain biotic or abiotic conditions to be manifested

• Noninteractive : mechanisms that may not require interactions between individuals to be expressed

• Interactive : mechanisms that may require interactions between individuals to be expressed

Biological mechanisms producing size variationamong larvae (2)

Adapted from Huston & DeAngelis, Am. Nat., 1987

Noninteractive InteractiveInherent

Imposed Temporal heterogeneityHatchingTemperaturePhotoperiod & light intensity

Spatial heterogeneityAbiotic resourcesFood availability/sizeTemperature

Change in morpho-physiology

MortalityCannibalismDensity-dependent

CompetitionPhotoperiod & light intensityTurbidity Food availabilityStocking density

Genetic variationChange in morpho-physiology

MortalityDensity-independent

Selection of experimental variablesEurasian perch & European seabass as comparative models

Hatching time

Initial heterogeneity

Stocking density

Population

Temperature

Photoperiod

Light intensity

Abiotic environment

Feeding level

Food composition (live/dry food ratio)

Feeding

Size variation

survival - cannibalism growth

Feed intake Digestion process

General methodologyFacilities and fish• Sibling fish reared in recirculating system, under optimal physico-chemical conditions for both species

• 2 stages of development : larvae and post-larvae (weaning stage)

Feeding• Artemia nauplii from day 3 to day 21 in perchlarvae

• Brachionus plicatilis then Artemia nauplii inseabass larvae

• Weaning phase in both species by progressive replacement of Artemia nauplii by dry food

Population variables

Hatching timeMaterial & Methods

• Rearing of larvae hatched from the same egg batches in pure (same age larvae) or mixed (different ages) populations

• Labelling of larvae hatched on day 3 (perch) or on day 1 (seabass) by immersion in alizarine red solution

• Identification of labelled larvae inthe final sampling by observation oflabelled otoliths in epifluorescence microscopy

Population variables

Hatching time in perchResults

0%10%20%30%40%50%

D1+2

60%

D3 D1+2+3

a b b

Survival

0

20

40

60

80

D1+2

mg

D3 D1+2+3

a b b

Final weight

0%10%20%30%40%50%

D1+2

60%

D3 D1+2+3

CVweight

a b

initialfinal

0%5%

10%15%20%25%

initial finalD1+2

a bProportion of larvae hatchedon D1+2 in D1+2+3 mixedpopulation

Population variables

Hatching time in seabassResults

0%10%20%30%40%50%

D1

60%

D2 D3

a a a

Survival

ba

D1+2 D1+30%

10%20%30%40%50%

D1

60%

D2 D3

CVweight

a

D1+2 D1+3

a a ab

initialfinal

020406080

100

D1 D1 D1 D1

D2 D2 D3 D3*

initial initial finalfinal

D1+D2 population

D1+D3 population

%

Proportion of larvae hatched on day 1 within the initial and final mixed populations

Population variables

Initial size heterogeneityMaterial & Methods

Perch : larvae of 9mg and post-larvae of 85mg

Seabass : post-larvae of 33mg

- Standard heterogeneity : larvae of same age reared under standard conditions

- High heterogeneity : larvae reared at 2 different densities to create size differences

- Controlled heterogeneity : same as standard, but weekly size-sorting of fish by removing potential cannibals and replacing them by medium size

Population variables

Initial size heterogeneity in perchResults

• No significant effect of size-sorting on survival, cannibalism and growth in perch larvae

• A significant increase of mortality due to cannibalism at high initial heterogeneity in perch post-larvae

2030405060

CVw

eigh

t(%

)

0 3 6 9 12 15 18 21days

70

Larvae0

10

standardhighcontrolled

2030405060

CVw

eigh

t(%

)

0 3 6 9 12 15 18 21days

70

Post-larvae0

10

• A fluctuating evolution of size heterogeneity due to a combination of differential growth and differential mortality

Population variables

Stocking densityMaterial & Methods

Perch

- Low density : 10 fish L-1

- Medium density : 32 fish L-1

- High density : 100 fish L-1

• Post-larvae (178 mg) - Low density : 1 fish L-1

- Medium density : 3.2 fish L-1

- High density : 10 fish L-1

• Larvae (0.9 mg)

Seabass

• Post-larvae (26 mg) • Larvae (0.45 mg)

50 - 100 - 150 - 200 fish L-1 5 - 10 - 15 - 20 fish L-1

Stocking density in perchResults (1)

Population variables

0

5

10

15

20%

10 32 100 fish L-1

Survival

a bab

0

20

40

60%

10 32

Cannibalism

a abb

100 fish L-1

Larvae

0

25

50

75

100%

1 3.2 10 fish L-1

Survival

a ba

0

10

15

20%

1 3.2

Cannibalism

a

b

a5

10 fish L-1

Post-larvae

Population variables

Stocking densityin perchResults (2)

Larvae0

10

20

30

0 5 10 15 20 25

5

15

25Final weight distribution

%

Weight (mg)

10 fish L-1

32 fish L-1

100 fish L-1

25

20

15

10

5

0

35

30

0 500 1000 1500 2000 2500

Initial and final weightdistribution

Weight (mg)

%

Initial

Final

1 fish L-1

3.2 fish L-1

10 fish L-1Post-larvae

Population variables

Stocking density in seabassResults

• No significant effect of stocking density in larvae but a significant increase of mortality and cannibalism at high stocking density in seabass post-larvae

0

20

6040

Survival (%)

0

2

5 10 15

Cannibalism (%)

4

6

8

80

a b c c

a b c c

20 fish L-1

25

20

15

10

5

0

35

30

0 50 100 150 200

u

Final weight distributionN fish

Weight (mg)

5 fish L-1

10 fish L-1

15 fish L-1

20 fish L-1

Environmental variables

Temperature in perchStocking of newly-hatched larvae in 10-m2 tanks during 45 days at 3 temperatures : 17°C - 20°C - 23°C

0

10

20

30

40%

17°C 20°C 23°C

Survival

a b c

0

200

400

600

800mg

17°C 20°C 23°C

Body weight

a a b

0

2

N m-2

17°C 20°C 23°C

Cannibals

4

6

8

a b b

0

1000

2000

3000

4000mg

17°C 20°C 23°C

Body weightcannibals

b ba

Environmental variables

Temperature in perch (2)

10080604020

0

Cannibals N = 7

Frequency (%)

10080604020

0

Cannibals N = 63

10080604020

0100 31001100 41002100

Cannibals N = 76

Body weight (mg)5100 5900

17°C

20°C

23°C

Cannibals N=7

Cannibals N=63

Cannibals N=76

PhotoperiodEnvironmental variables

0

20

40

60% Survival

0

10

20

30% Cannibalism

0

20

% Final CV weight

12:12 16:8 24:0

40

abab ba

cab bca

6080

Light:dark 8:16 12:12 16:8 24:0

Light:dark 8:16

Perch larvae Seabass larvae

%

0

20

40

60% Survival

0

20

8:16 12:12 16:8

Final CV weight

40aa ba

6080

No cannibalism

8:16 12:12 16:8 24:0 Light:dark

24:0 Light:dark

Feeding variables

Feeding level in perch larvae

0

20

40

60

% Survival

0

5

10

15%

Cannibalism

bb ba

80

1 5 10 20% biomass

ba ba0

20

% Final CV weight

40

abab ba

60

1 5 10 20% biomass

0

20

40

10

mg Final weight

ba ba

50

30

ConclusionsA tentative summary of size variation causes

• Hatching time• Initial size variation• Stocking density

• Temperature• Photoperiod• Light intensity

• Feeding level• Food composition

Population

Environment

Feeding

Perch SeabassLarvae Post

larvaeLarvae Post

larvae

+--

--

+--

+-

++

---

?++?

?--

+ +-

? ?+

++++

? +

Conclusions (cont.)

• many factors are susceptible to induce or enhance growth depensation and multimodality in cultured larval population

• imposed, interactive variables (initial size variation, density)appear to affect predominantly survival and growth rather thanfinal size variation

• imposed, non interactive variables (temperature, photoperiod, food availability) appear to affect predominantly final size variation, either directly or indirectly via interactive mechanisms such as cannibalism and size-dependent mortality