The document summarizes research on tilapia conducted at the Institute of Aquaculture. Key points include: 1) Research has studied tilapia genetics, nutrition, disease, and reproduction since 1978. 2) Studies have focused on developing all-male strains using techniques like hormone treatment and chromosome manipulation. 3) Recent work shows photoperiod control and continuous low light can improve spawning activity, fecundity, growth rates, and production cycles in tilapia.

1. CEFAS Tilapia Workshop
18th June 2009
Tilapia Research
Institute of Aquaculture
Professor Brendan McAndrew

2. Introduction
 There has been research on tilapia
undertaken at the IoA since 1978
 Much of this early work funded by UK
overseas development funds.
 Wide range of subjects studied -
genetics, nutrition, disease,
reproductive biology.
 Stirling strains widely used by
industry

3. Background
 Tilapia species gathered from wild in Africa.
 All collections checked using morphological as
well as genetic techniques to ensure purity.
 Early work repeated existing studies to obtain
baseline results on known genetic material –
hybridisation both intentional and unintentional
was widespread in commercial strains making
identification difficult.
 Single sex tilapia has been an ongoing research
topic.

4. MIXED SEX V’S MONOSEX TILAPIA
Mixed SexTilapia All Male Tilapia

5. TILAPIAS (Oreochrom is spp.)
• Monosex male culture offers a solution to reproduction
before harvest: this has been achieved by hormonal
masculinisation or through genetic techniques
• Sex determination appears to be largely genetic and
monofactorial below about 34oC, but differs between
species in the genus (O. niloticus and O. mossambicus
XX/XY, O. aureus WZ/ZZ). YY males viable.
• Above about 34oC, temperature affects sex ratio,
largely through masculinisation of genetic females
• No identification of sex chromosomes or sex-linked
markers until recently - being developed at IOA

6. Manipulation of sex-ratios in tilapia
• Hand sexing, 30g+ fish sexual dimorphism
• Hybridisation, Widely abused, niche use.
• Hormones
•Hormonal sterilisation- unacceptable today.
•Direct - larvae/fry are treated with steroid hormones
during sexual differentiation to change sex ratio.
•Indirect - sex determination system is manipulated in
broodstock to result in progeny which are all genetically
the same sex.
• Temperature dependent sex-determination. 34-38 C can
change phenotypic sex. female-male

7. Hormone sex-reversal
 Exogenous hormone swamps natural
hormone changes that cause sexual
development.
 Phenotypic change of sex the neomales or
neofemales produced are still the same
genetic sex.
 Simple highly efficient technique small
amounts of hormone applied for labile
period.
 EU regulation does not allow direct
application in human food chain.

8. According to EU Directive 96/22/EC (entry into force 23 May 1996),
• Contamination from substances with hormonal action and other substances. According to EU Directive
96/22/EC (entry into force 23 May 1996), Member States shall prohibit: (a) the placing on the market of stilbenes,
stilbene derivatives, their salts and esters and thyrostatic substances for administering to animals of all species
and (b) the placing on the market of betaagonists for administering to animals, the flesh and products of which are
intended for human consumption.
They shall, also, prohibit (i) the administering to a farm or
aquaculture animal of substances having a thyrostatic, androgenic
or gestagenic action and of betaagonists, (ii) the holding of animals
on a farm, the placing on the market or slaughter for human
consumption of farm animals or of aquaculture animals which
contain the substances referred or in which the presence of such
substances has been established, (iii) the placing on the market for
human consumption of aquaculture animals to which substances
have been administrated and of processed products derived from
such animals,

9. HORMONAL SEX REVERSAL
Labile period will vary
depending on species 10
LABILE PERIOD days for tilapia 100 days for
trout and seabass
F H YSR SD
DELIVERY
HORMONE
START TIME HIGH RATE OF SEX REVERSAL
DURATION
CONCENTRATION HIGH SURVIVAL RATE
COMPETITION
NATURAL FOOD
F = Fertilisation; H = hatch; YSR = yolk sac resorption; SD = sexual differentiation

10. Direct treatment
Dose between
30-60ppm 17- α Methyltestosterone
(MT)
 Dose will depend on wide range of
parameters but must be started
before 10 days post hatch, swim-up
stage.
 This require hatcheries to have tight
control over fry collection usually
egg-robbing and artificial incubation
to get the best % reversal.

11. Indirect hormone treatment
 This technique is normally used to generate a
specific sex determination genotype.
 In tilapia we want an all-male system in a
heterogametic species. E.g. XY male XX female.
 We need to develop YY males or ZZ females.
 In fish there are several ways to achieve this
result depending on the levels of sophistication
available.
 Hormone never used in the production fish.

12. Genetic all-male production in an
XX/XY species – Nile tilapia
using hormone treatments
Process involves several labour intensive progeny (after Mair et al, 1991)
testing stages.

13. Chromosome set manipulation
Induction of gynogenesis in fish
2nd meiosis 1st mitosis
genome 50%
oogonia duplication 1st meiosis 2n
replication
1st polar body
2nd pb
n
Fertilise with
UV irradiated
sperm
2n
ovulation
100%

14. YY male O. niloticus :
Mitotic Gynogenesis
F0 XX female XY male
DES
F1 MITOTIC GYNOGENESIS
XX female XY neofemale
F2
P
XX females
r YY males
o
Progeny testing will identify neofemales
g
e

15. YY male production :
Androgenesis
FRESH SPERM
Late shock
1st mitotic division
Mixed XX females and YY
males.
Haploid embryos

16. Partial pedigree of androgenetic male O.niloticus and the % males in progeny
when crossed to normal females.

17. All-male Stirling red tilapia
 Developed from pure Egyptian
O.niloticus.
 Dominant red gene- no
melanophores in the epidermis.
 Pure breeding strains available,
widely distributed.
 Androgenesis used to produce YY
males and can be supplied to
generate all-male fry in Stirling
strain.

18. This is the latest generation of Stirling red tilapia YY male

19. Chromosome set manipulations
 Offer rapid way to generate new
genotypes such as YY males.
 Useful technology to study the
inheritance of sex-determination
mechanisms and other complex
traits.
 Useful technology for gene mapping.
 Triploidy- not yet commercial reality.

20. Temperature sex-determination
 Evidence that sex-ratio can be biased
towards males by raising individuals from
susceptible families at +34 C.
 Selection for lines that produce a higher
male % has shown improvements upto
90% male.
 Evidence from high %male lines that high
temperature can reduce this %.
 Is this line worth pursuing?

21. Reproductive biology of tilapia
Hatchery production of
tilapia fry relatively inefficient
-low fecundity
-asynchronous spawning
-need large numbers of
females
-hormonal control of
reproduction has not worked
-evidence that light is a major
cue and that tilapia respond
to day length and intensity

22. Photoperiod experiments
 Female Nile tilapia from same family
ongrown under identical conditions to
maturity.
 Separated into four different light
regimes 6D:18L, 12D:12L, 18D:6L
and 24L.
 Females maintained on these
regimes for 6 months and spawning
activity monitored.
 All eggs counted and measured.

23. Photoperiod control of reproduction
in tilapia
Number of Spawns Egg production
Total per month 6L:18D 12L12D 18L:6D 24L
100 50000
80 40000
Spawns
60 30000
Eggs
40 20000
20 10000
0 0
6L:18D 12L:12D 18L:6D 24L Sep-01 Oct-01 Nov-01 Dic-01 Ene-02 Feb-02
Inter-spawning-interval
Extended day lengths (18,24hr)
25
increased spawning activity –reduced
20
ab b
Inter Spawning Interval (ISI).
15 ac
days
c
10 Highest and most consistent egg
5 product in 18hr day
0
6L:18D 12L:12D 18L:6D 24L
(Campos-Mendoza et al 2004)

24. Photoperiod
Fecundity
Fecundity (x1000) Relative fecundity (egg/g) Longer days increased
8 relative and total fecundity
7
Number of eggs
6
a b
5
b b
4
3
2
1 b b a a
0
6L:18D 12L:12D 18L:6D 24L
1.2 Diameter mm Volume mm3
1
Shorter ISI resulted in more
y = 0.4405x + 0.2616 but smaller eggs
0.8 R2 = 0.3539; p 0.000
0.6
Log10 mm
0.4
0.2 y = 0.1517x + 0.1938
R2 = 0.3202; p 0.000
0
(Campos-Mendoza et al 2004)
1 1.2 1.4 1.6 1.8 2
Log 10 ISI

25. Potential for photoperiod control
 18L:6D produced 58% more eggs than the
ambient 12L:12D photoperiod.
 Fish under 18L:6D significantly higher
total and relative fecundity, reduced ISI
and greater clutch size.
 Some photoperiod better than continuous
light – entrain rhythm.
 Further work on mechanism underway.
 Evidence that they are very sensitive to
light.

26. Light Intensity - growth
 Recent work has shown that growth
performance can be improved by using
continuous medium to low lighting
regimes.
 Up to 20% improvement in weight at 118
dph under experimental conditions needs
to be repeated under commercial
conditions.
 In other species benefits not seen until
later growth stages.

27. Table 1. Light intensities in Watts m-2 and Lux (mean SE)
measured at the bottom and surface of the tanks for each
experimental treatment during day time.
Treatment Watts m-2 Lux
LL High top 3.0 0.2/ 684.0 32.0/
bottom 4.6 06 1031.0 104.0
LL Medium 0.5 0.1 / 141.5 17.5/
0.7 0.1 172.5 10.5
LL Low 0.04 0.0/ 4.5 0.5/
0.0 0.0 8.0 1.0
Control 0.7 0.1 / 172.5 22.5/
0.9 0.2 190.5 30.5

28. Weight over time in Nile tilapia raised up to 118 days post hatch under different
light intensities (High LL, Medium LL, Low LL and Control 12L:12D). Values are
expressed as mean SE (n = 33-75 / replicate). Superscripts indicate significant
differences between treatments at a given time point.

29. Different photoperiod control systems
widely used in fish culture in NW Europe
to control sexual maturation and improve
growth performance in salmon, trout and
marine species.
> 30% improvement on growth
performance with extended days.

30. Extended day-length in
hatchery likely to improve
fry yields.
Extended day-length in
ongrowing likely to
improve overall growth
rate –shorter production
cycles.
Genomic techniques
being used at the
moment to study many of
the traits described- new
developments to come
New light technology used by cod farming
operations in Norway and Scotland.

31. Scientists involved
 Dr David Penman
 Dr Hérve Migaud
 Dr Jim Myers
 Dr M. Gulam Hussain
 Dr Antonio Campos-Mendosa
 Dr Rafael Campos-Ramos
 Dr Antonio Mendoza.
 Dr Chris Martinez.