Fish reproduction razia 2

Knowledge Bank

1. Topics to be covered
•Reproduction
•Life cycles
•Growth
Reproduction, Early Life Stages, Growth
(Chapter 6 and additional material)

2. Reproduction – hormones of the reproductive
system
•Brain-hypothalamic hormones (note error in textbook)
Gonadotropin-releasing hormone (GnRH)
Gonadotropin release-inhibitory factors (GnRIF; such as
dopamine)
•Pituitary hormones: gonadotropins
FSH: controls gonadal growth
LH: controls gamete maturation and release
•Gonadal hormones (steroids)
11-ketotestosterone (androgen)
17b-estradiol (estrogen)
Progesterone or its derivatives (progestins, they induce
gamete maturation and ovulation; Maturation-Inducing
Hormone = MIH)
Reproduction, Early Life Stages, Growth

3. Reproduction – general environmental regulation
brain
gonad
Fish
pituitary
steroid hormones
Environment
seasonal photoperiod profile
seasonal temperature profile
food availability
contaminants
other liver
LH
FSH
•androgens
•estrogens
Vg
gonadal
development
•progestins
Reproduction, Early Life Stages, Growth

4. Brain
Pit
Gonad
dopamine
-
LHRH
+
LH
Gametes
Reproduction – hormones that control release of
gametes
Reproduction, Early Life Stages, Growth

5. Reproduction – captive spawning
•Captive spawning is preferred over collection of natural seed
because,
Greater control over timing of seed availability
Greater control over number of available seeds
•Many of the current aquacultural species do not spawn naturally in
captivity
•Often, problem is with the spawning of captive female, not male,
fishes
•Methods for natural and hormonally induced spawning of captive
fishes and other aquacultural organisms have been developed based
on knowledge of their reproductive physiology
Reproduction, Early Life Stages, Growth

6. Reproduction – captive natural spawning
Zebrafish spawning
•photoperiod - 14L:10D
•temperature - 28~29 °C
•spawning container overnight
spawning containers
fish in spawning
containers
Reproduction, Early Life Stages, Growth

7. Reproduction – captive induced spawning
MIH
MIH
R.W. Rottmann et al. 1991
LHRH = GnRH
Reproduction, Early Life Stages, Growth

8. Reproduction – captive induced spawning
R.W. Rottmann et al. 1991
MIH
hCG = human chorionic gonadotropin
Reproduction, Early Life Stages, Growth

9. Reproduction – shellfish
•Decapod crustaceans
X-organ/sinus gland system of eyestalk produces gonad-
inhibiting hormone
Eyestalk ablation removes gonad-inhibiting hormone and
causes completion of gametogenesis in male and female
decapod crustaceans (in some species, eyestalk can
regenerate)
•Bivalves
Spawning cues include change in water temperature,
change in salinity, lunar cycles, pheromones
Reproduction, Early Life Stages, Growth

10. Reproduction, Early Life Stages, Growth
Early life stages
•Fertilization leads to Zygote
•Depending on species, embryogenesis occurs over period of hours
to weeks
•Following hatching, several stages of development can be described:
Embryo-larval transition (endogenous feeding)
Larval development
Larva-juvenile transition (metamorphosis)
Juvenile (prepubertal) growth
Embryo-
larva
transition

11. Reproduction, Early Life Stages, Growth
Early life stages
•Embryo development (endogenous nutrition)
Days to weeks
Need to clean egg mass following fertilization
Use clean water for incubation (filtered water)
Keep good levels of oxygen
Appropriate temperature
•Embryo-larva transition (fishes – endogenous nutrition)
Days to weeks
Culture techniques similar to embryo
•Larval development
Days to weeks
Onset of exogenous feeding; providing appropriate food
becomes major aspect of rearing (microalgae for molluscs
and shrimps; rotifers and brine shrimp nauplii for fish and
older shrimp larvae)
Nitrogenous waste can become problem; need close
monitoring of general water quality - rearing often occurs in
large tanks to help with water quality
Density of larvae reduced as they grow

12. Reproduction, Early Life Stages, Growth
Early life stages (continued)
•Larval development is abbreviated or non-existent in some species
(direct development)
Embryos hatch already bearing juvenile form
•Larva-juvenile transition: metamorphosis
Slight to marked changes in morphology, physiology and
behavior, depending on species
•Juvenile development
Postmetamorphic juvenile fishes are progressively weaned
off live feeds on to artificial diets
Initial culture is in hatchery tanks
•Grow out
Final phase of culture when juveniles are grown until
harvested

13. Reproduction, Early Life Stages, Growth
Growth
•Bioenergetics
Energy equations (note: specifics here are different from text
but overall meaning is same)
Simple equation: p x F = M + G
p = proportion of food consumed that is assimilated
F = amount of food consumed
M = catabolism (energy release)
G = growth (anabolism)
Expanded equation: C = (Mr + Ma + SDA) + (F + U) + (Gs + Gr)
C = rate of energy consumption
Mr = standard metabolic rate (rate of energy use by a fasting animal at rest)
Ma = metabolic rate increase (over standard) due to activity
SDA = metabolic rate increase (over standard) due to digestion and assimilation of
food
F = waste due to egestion (feces)
U = waste due to excretion (urine)
Gs = somatic growth rate
Gr = reproductive or gonadal growth rate

14. Reproduction, Early Life Stages, Growth
Growth
•Patterns of growth of an organism can be described in several ways:
Absolute growth: increase in size (length or weight), equal
Y
2-Y
1
Absolute growth rate: increase in size per unit time, equal
(Y
2
-Y
1
)/(t
2
-t
1
)
Initially small, but as animal grows in size, there is
increased capacity to take in and assimilate food
Relative growth: increase in size relative to initial size,
equal (Y
2
-Y
1
)/Y
1
Relative growth rate: increase in size per unit body size
per unit time, equal (Y
2
-Y
1
)/[Y
1
(t
2
-t
1
)]
Initially rapid, but slows down with development
Inflexion point

15. Reproduction, Early Life Stages, Growth
Growth
•Measuring growth:
Growth measurements are needed to monitor health and
predict harvest time
Measures
 Length: linear dimension using calipers or ruler - quick and easy
 Wet weight: most common assessment of whole body growth of
fishes - quick and easy
 Dry weight: wet weight minus water (in oven at ≤100°C). Can
usually be applied only on dead organism; it is most accurate
method for assessing animal tissue growth, since changes in tissue
water content may occur due to stress etc.
 Condition factor: weight/(length)
3
 Ash-free dry weight: dry weight – inorganic ash (up to 24 h at
500°C). It is the dry weight of organic matter in the animal. Useful
for animals with large inorganic components (e.g., bivalves) where it
is relatively difficult to measure organic tissue content. Sometimes
simply expressed as ash weight.
 Proximate composition: determination of different categories of
compounds in tissues. Most commonly measured categories
include carbohydrates, proteins, lipids.

16. Reproduction, Early Life Stages, Growth
Growth
•Measuring growth in fishes:
Length measurements
Total length (TL): tip of snout to tip of longest caudal fin
rays. Difficult to measure accurately if caudal fin is
damaged
Fork length (FL): tip of snout to fork (median caudal fin
rays). Used in fishes with clear forks
Standard length (SL): tip of snout to base of caudal fin (or
tip of notochord in larval fish)

17. Notes on Chapter 6 reading material
•Subsections 6.3.1, 6.3.2, and 6.3.3, 6.4.2: general knowledge of topic covered in
these subsections is necessary, but no need for details
•Formulas in subsection 6.4.1 are not required reading (you must instead know
formulas covered in class)
•Under subsection 6.4.4, discussion of bivalves and decapod crustaceans is not
required reading
•Table 6.2 is not required reading
Reproduction, Early Life Stages, Growth