FISH GROWTH

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CHAPTER 2 FISH GROWTH
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1. GENERAL ASPECTS OF FISH GROWTH growth an
increase in size (or cell number) over time,
accompanied by a positive energy
balance endotherms (birdsmammals) determinate
growth (typically little growth after maturation)
? fishes indeterminate growth growth continues
after maturation, throughout life cycle fish
growth is often periodic seasonal variation in
temperature, food availability, spawning
activity, etc. can cause seasonal growth cessation
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• if periods are regular, a growth record is formed
  in hard structures scales, fin spines or rays,
  vertebral centra, opercle bones, ear bones
  (otoliths)
• periodic growth marks allow estimation of growth
  rates by counting and measuring distances between
  growth checks

growth ridges (circuli) in a trout scale ?
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• - growth curves depict size (length or weight)
  against age growth rate is slope of this curve
• shape of growth curve is usually sigmoidal
• slow approach of plateau, rarely if ever
  achieved limits to ultimate size are biotic
  (food availability, metabolic efficiency) and not
  mechanical
• growth rate in ectotherms only 1/10 1/30 of
  those of birds or mammals of the same mass

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2. MEASURES OF FISH GROWTH Growth of a fish may
be assessed by measuring its size at various
ages. Fish size may be measured by weight or by
length. Length is usually preferable to weight,
because length is well correlated with sizes of
hard structures used in aging and weight can be
variable with the seasons. standard length (in
mm) From tip of snout to posterior end of
hypural bone (caudal fin base). This is the most
reliable indicator of fish length as it is not
subject to variation in fin length or damaged
caudal fins. fork length (in mm) From tip of
snout to end of median caudal fin rays. Common
measure in Canadian fish management. total
length (in mm) From tip of snout to maximal
extent of caudal fin. Common measure in American
fish management.
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total body weight (in g) Fresh wet specimen
weight. Small specimens should be blotted and
large specimens should have stomach contents
removed (especially piscivores). condition
factor k weight x 100
length3 specific growth
rate SGR (ln Wfinal ln Winitial) x 100

time
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Determination of growth empirical By stocking
tagged fish of a known age (e.g. hatchlings) in a
natural water body, then actively sampling the
population at set intervals. Overstocking must be
avoided as growth rates may be affected.
Peterson method (length-frequency method)
Lengths are taken from a large random sample of a
population. Number of individuals caught are
plotted against length. The resulting plot should
reveal clusters indicating year classes,
beginning with year zero. Population sampling
must be random, however. Random sampling may be
hindered by varying success in capturing small
young of the year versus adults or by age classes
segregating into different habitats.
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anatomical structures Counting annuli on hard
(bony) structures is the most common method of
aging fish. This relies on seasonal variation in
deposition of bone. Summer growth of bone is
represented by dense wide bands of growth (opaque
zone) separated by narrow less dense winter
growth (hyaline zone). Summer growth of scales is
represented by widely separated circuli and
winter growth is represented by more closely
spaced weak (and often incomplete) circuli.
Determining age from such structures is analogous
to determining tree age. scales Easily acquired
structure for aging and is not lethal. There are
many problems in examining scale ages though
false annuli, regenerated scales, and annuli may
be difficult to observe.
fin rays Easily acquired structure for aging and
is not lethal. Cross-sectioned to observe
internal annuli. otoliths Technically not bone,
but cross-sectioning reveals internal annuli.
? bones Cleithrum, opercular, preopercular, etc.
usually have well developed annuli.
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• Biochemical parameters to describe and measure
  growth
• incorporation of radiolabeled amino acids into
  scales
• nitrogen retention ( measure for protein
  synthesis and therefore growth of lean body mass)
• RNA/DNA ratio ( measure for protein synthesis)

• For the physiologist or biochemist, these growth
  descriptors are more useful (positive energy
  aspect)

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3. FACTORS AFFECTING FISH GROWTH Bioenergetic
equation (Brody, 1945) E M P U F E
total amount of energy expended M energy
expended for maintenance and activity (or
metabolism) P energy for production ( growth
reproduction) U energy lost in urine (mainly in
the form of nitrogenous wastes) F energy lost
in feces (predominantly as undigested food)

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Note 1. The boundaries of these categories are
not clear should the cost of territorial defense
or of food gathering to feed young be included
under P (reproduction) or M (activity)? 2. Energy
for growth is a trade-off with energy for
reproduction

• general pattern grow first, then reproduce
• size ? ? fecundity ? (females)
• ? territorial success ? (males, females)
• ? metabolic efficiency ? (to a point)

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- factors in the internal or external environment
that increases or decreases E - food
abundance, food size, food digestibility (see
further) - competition with other fish for
food - time spent hiding from or escaping
predators - time spent defending a territory -
factors in the internal or external environment
that increases or decreases M - temperature
(see further) - water quality salinity, oxygen
availability - pollution toxins, NH4, heavy
metals,... - parasites
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Percent weight gain (A), specific growth rate
(SGR) (B), condition factor (KF) (C), and muscle
ratio (MR) (D) for saline-injected fish (black
bars) and LPS-injected fish (gray bars). Values
for weight gain and SGR were calculated and
shown for the entire 43-day study, while KF and
MR are shown for day 43. Significant differences
between saline- and LPS-injected groups are
indicated by a (Student's t-test, P lt 0.05
weight gain, SGR, KF, and MR were determined for
each tank, then averaged by treatment n  3).
(From Johansen et al., 2006) LPS
lipopolysaccharide (bacterial cell wall)
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• age, size, maturity, sex

• growth decreases with age (increasing allocation
  to reproduction, increasing allocation to
  maintenance?)
• growth curves often differ between sexes
  (different age of maturity, differing level
  allocation to reproduction, other intrinsic
  differences)

- ration food intake, food availability

• growth will increase with ration, but at
  decreasing rate
• maintenance ration no growth
• optimum ration best conversion above this
  growth efficiency declines

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- temperature

• temperature influences a number of processes
  affecting growth
• maintenance needs increase with temperature at
  accelerating rate
• maximum rations increase, then fall off
• if food is limited, lower optimum temperature
  (extreme case starving fish tend to choose
  colder water than fed fish)

- genetics

• populations and strains known to vary in growth
  rate
• example the Atlantic silverside (Menidia
  menidia)

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High-latitude (northern) fish have a higher
genetic capacity for growth and grow 2 to 3 times
faster within the growing season than do
low-latitude (southern) fish (consume more food
and utilize more efficiently). This
"countergradient variation" in growth rate is now
known to be widespread in fishes and may provide
a general model for choosing natural stocks to be
used in aquaculture natural populations with the
highest capacity for growth may be found where
the growing season is shortest.
Studies on Atlantic silversides, striped bass,
and the common mummichog prove that northern
strains grow much faster than those from the
south under intensive aquaculture conditions.
Atlantic silverside
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4. HORMONAL CONTROL OF FISH GROWTH food intake ?
carbohydrates fats proteins

metabolism (1) energy supply (2)
building blocks for growth and reproduction
hormones
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Many hormones are involved in the regulation of
growth in fish GH, gonadal steroids, thyroid
hormones, insulin, IGF-I, ...

• 4.1. Growth hormone and IGF-I
• peptide (187-188 amino acids) produced in
  somatotropic cells of pars distalis of pituitary
• important functions in fishes growth
  osmoregulation ( reproduction)
• - regulation of GH release very complex!
• control by hypothalamic factors
• - growth hormone-releasing hormone (GHRH)
  stimulatory
• - somatostatin (SS SRIF SRIH) inhibitory
• (but also GnRH, NPY, CCK, BBS, IGF-I,...)

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General scheme of the GH/IGF axis
Hypothalamus GHRH SS
GH Pituitary Liver
IGF-I
GH-R
GH-R
Target tissues METABOLISM GROWTH
IGF-R
stimulation inhibition
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Amino acid sequence of GH in Oreochromis
mossambicus MNSVVLQLSVVCLGVSSQQITDSQRLFSIAVNRVTHL
YLLAQRLFSDFESSLQTEEQRQLNKIFLQDFCNSDYIISPIDKHETQRSS
VLKLLSISYGLVESWEFPSRSLSGGSSLRNQISPRLSELKTGILLLIRAN
QDEAENYPDTDTLQHAPYGNYYQSLGGNESLRQTYELLACFKKDMHKVET
YLTVAKCRLSPEANCTL Amino acid sequence of IGF-I
(precursor) in O. mossambicus MSSALSFQWHLCDVFKSAM
CCISCSHTLSLLLCVLTLTPTATGAGPETLCGAELVDTLQFVCGERGFYF
NKPTGYGPSARRSRGIVDECCFQSCELQRLEMYCAPVKTPKISRSVRSQR
HTDMPRAPKVSSRANKGTERRTAPQPHKTKNKKRPSPGHSSSFKEVHQKN
SSRGSSGGRNYRM
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Metabolic actions of GH and IGF-I
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• Important effects of GH/IGF-I
• Stimulation of proliferation of chondrocytes
  (cartilage cells) ? skeleton growth
• Stimulation of differentiation and proliferation
  of myoblasts and amino acid uptake en protein
  synthesis in muscle ? muscle growth
• Stimulation of protein anabolism increased amino
  acid uptake, increased protein synthesis and
  decreased breakdown of proteins for energy supply
• Stimulation of fat catabolism mobilization and
  utilization of fat as main energy source
• Stimulation of appetite (food intake)
• Improvement of food conversion efficiency (less
  food needed for the same growth)

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• 4.2. Other hormones
• insulin accelerates amino acid uptake and
  protein synthesis in muscle (similar to GH),
  general mitogen and growth promoter
• thyroid hormones
• basal levels necessary for normal growth!
• low dose positive effect on growth (increased
  energy production from glycogen and fat ? amino
  acids can be used for protein synthesis)
• high dose negative effect on growth (energy
  demand is too high ? amino acids used for energy
  production)
• thyroid hormones facilitate the effects of GH
• sex steroids, especially androgens anabolic
  growth-promoting effects

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rapeseed Brassica napus
(from Burel et al., 2000)
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• 4.3. Feeding strategies and hormones
• food deprivation (starvation) ? severe growth
  impairment
• GH? due to GHR? (and therefore IFG-I?)
• T3? for energy saving (energy shifted to basal
  processes)
• modulation of feeding regimes
• refeeding after fasting compensatory growth
  (catch-up growth) growth rate during refeeding
  exceeds normal growth rate!
• application in aquaculture ? duration and
  frequency of feeding cycles need to be optimized
  for each species, which costs time and effort

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Response of mean body weight of hyrbid striped
bass fed on a normal (control) and cycled
(treatment) regimen. Gray bars denote periods of
restricted feeding in the treatment group.
Asterisks represent significant differences
between groups (P lt 0.01 P lt 0.001)
(N  67158 animals/group). (from Picha et al.,
2006)
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? Hepatosomatic index (HSI) of hybrid striped
bass fed on a normal (control) and cycled
(treatment) regimen. Gray bars denote periods of
restricted feeding in the treatment group.
Asterisks represent significant differences
between groups (P lt 0.001) (N  12
animals/group). (from Picha et al., 2006)
? Responses of (A) feed consumption ( body
weight consumed/day) and (B) feed conversion
ratio (FCR) for fish fed on a normal (control)
and cycled (treatment) regimen. Data are shown
for time periods that reflect the treatment
refeed periods only. Asterisks represent
significant differences between groups
(P lt 0.05 P lt 0.01) (N  2 tanks/group).
(from Picha et al., 2006)
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Responses of (A) plasma IGF-I and (B) hepatic
IGF-I mRNA in hybrid striped bass fed on a normal
(control) and cycled (treatment) regimen. Gray
bars denote periods of restricted feeding in the
treatment group. Asterisks represent significant
differences between groups (P lt 0.05
P lt 0.01 P lt 0.001) (N  12). (from Picha
et al., 2006)
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• 5. MANIPULATION OF FISH GROWTH
• - methods of phenotype manipulation
• - genetic selection
• - direct hormone therapy
• - genetic engineering (transgenic fish)
• Example transgenic fishes containing extra
  copies of GH gene
• ? Issues posed by transgenic fishes
• - food safety
• - environmental safety
• - public policy

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Fish from eggs injected with GH gene
Atlantic salmon expressing GH transgene
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• 5. NEUROPEPTIDES AND THE CONTROL OF FOOD INTAKE
  IN FISH
• Method
• injection of substances into brain ventricle
  (intracerebroventricular injection)
• comparison of brain distribution of substances
  (or their receptors) with brain areas known to be
  involved in the control of food intake (
  hypothalamus)
• blocking receptors of putative substances
  controlling food intake
• ? effect on food intake in fish, mainly goldfish

?? See article by Volkoff et al., General and
Comparative Endocrinology 142 (2005) 3-19
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CONCLUSIONS The growth process and its control
by hormones is a very complex process. A number
of factors involved in the (control of the)
growth process remain to be discovered in
fish. Our current knowledge of fish growth is
very fragmentary and mainly concerns carnivorous
species which make up only 15 of the species
used in fish farming. ? Further investigation is
needed!!