Age and growth

Presented by: Rabia Shehzadi
Roll No. 17130814-012
Msc.4
Presented to: Dr. Shahid Mehmood

What is age
•Age is a duration of life

1. At what age does a fish attain a
maturity
2. What is the perfect catchable or
mark able size of the fish
3. It helps to calculate the life span and
longevity of fish
4. It enables to estimate and compare
growth rates of fish in different
waters.
5. Good or bad growth can point out
the suitability for rearing and
stocking purposes
6. The timing of spawning migration of
given species can be worked out
Age and rate of
growth of fishes
dependence

Methods of age
determination
Length
frequency
method
Marking
or known
age
method
Interpretatio
n of layers
laid down in
hard part of
fishes
1. Otoliths
2. Opercula
3. Vertebra
4. Fin rays
5. scales
 Identification of annual marks
 Irregularities
 Validity of Annuli on scales as
year marks
 How to collect and clean the
scales
 Reading scales
 Body scale relationship
 Lees phenomenon

Workersscientist
• Rounsefell
• Everhart(!953)
• Lagler(1956)
• Ricker(1968)

1.Length frequency method
• Peterson method by C.G Peterson 1892
• Fact
• This method is basically depends on the fact that in population
of having single spawning season the individual length of fish
of each age group tends to form a normal distribution and the
that modes of length frequency distribution of successive age
groups are separated along the length axis.
• The length frequency distribution are produced by plotting the
length of individual sampled from a population against the
number of fish( frequency of each length caught).
• Age are determined by counting the peaks.

• The difference between age group 0 fish and age 1 fish is (49.0-
20.0)=29.0mm.
• In simply the growth in length during first year of life is 29.0mm. The
amount of growth decreases with increase in age during second year of
life from 29.0 mm to 24.0 mm.
• As seen from the graph the modal values of all three age groups of July
sample show a respective progressive trend in months of September as
well.

Lengths are easier to record and obtain than weights and are less
affected by length are less affected by environmental and biological
factors.
Basic requirements
1. Sample should be composed of large number of individuals
2. Sample should be good representative of all size and classes
3. Sampling should be done in restricted period of time.
But these conditions are seldom fulfilled especially most frequent
drawback in the selectivity of gear.
If we use a non-selective gear then this method fails to give a good
estimation or reliable data about older age groups because of their
increasing overlap in length distribution.

Disadvantage
1. Method is not suitable for small samples
2. Length frequency peaks correspond with fish up to first
two or three years only. For older fish the correlation is
very low and peaks are less distinct.
3. Many fish population particularly in tropical waters spawn
throughout years distinct years classes are therefore
difficult to be recognized in such settings
4. One or more year classes may be poorly represented or
may be absent.

• Satisfied for routine fisheries
• Satisfied for 2-3 years old fish and is best limited to species of
temperate waters with seasonal spawning activities.
• This method is also applied on scale less or other hard parts
where scales are not readable
• Poly modal length frequency distribution of older age groups
by normal curves by use of probability paper.

2. Marking or known age method
• Basic requirements for most accurately and in positive manner
1. Keeping hatchlings or larvae of fish under under observation till
desired period in hatcheries rearing ponds tanks or aquaria.
2. Introducing fish of known age in water where the species was not
previously present
3. The growth history may be followed up
4. Marking and releasing fish in their natural environment like river
lake etc. after making its initial length and weight measurements.
5. Recaptured at intervals of time and growth.

Disadvantage
1. Laborious time consuming and expensive
2. Waiting for years to follow up the growth rates
3. This method is only done in confined water areas where fishes are
under control
4. Most marking and tagging methods are not applicable to young fish
5. Most of the marked fish may not be recaptured.
6. Marking affects the growth of fishes . It may decrease the growth of
fishes.

3.Interpretation of layers laid down in hard parts of
fishes
• Counting annual layers(growth zones) in the hard part of fishes
• Year marks or annual rings
• These are formed in alternate slower and faster growth rates .The
faster growth rings are wider and dark in reflected light and pale in
direct light.
• While the slower growth rings are pale in reflected light while dark in
indirect light.

• In temperate water fishes the rings formation occur in spring season
when rapid growth is followed up after cessation period of winter so
their annual contrast of summer and winter are different.
• While in tropics , water temperature fluctuate rapidly so their rings
are not satisfied but many workers find annual rings on scales or on
hard parts. But many other estimates that these are not annual rings
these are due to fluctuation in chemical composition due to flood
supply or due to winter and summer temperature changes.
• But however they successfully find the age through scales or other
hard parts in different waters of tropical areas.

1.Otolith (determine age of fishes)
• It is the calcareous part also called earstones.
• Jones (1954)
• Hynes(1964)
• Scale less
• Three pairs of otoliths in all fishes three on each side of internal ear
• Largest three Otolith called saggita used for age reading

Major handicaps with Otolith
• Dissection of head
• Require great skills
• Very laborious
• Great skill expertise
• Time consuming
• May need to killing fish having irregular or small Otolith

Method
1. Removed by pair of forceps
2. Preserved in the mixture of 90 % alcohol and 10% glycerin.
3. Rounsefell and Everhart recommend 3% solution of trisodium phosphate
as preservative.
4. To obtain translucent section it is mounted with Canada balsam on slide.
5. When Canada balsam is hardened the Otolith are grounded and polished
and wash with benzene and place coverslip after put a fresh drop of
Canada balsam to examine.
6. Transparent zones appears light while opaque zones are dark while
examine in transmitted light.

2.Opercula
• The opercula bones are used for age determination by many workers like
Bardach (1955).
• Successful method
• Removed easily by twisted by figures. And put it into water and boiled for
2-3 minutes then remove body flesh and skin by cloth.
• Dry it and observe under the binocular microscope.
• Alternate opaque and translucent zones are determined.
• To observe by reflected light against dark background soak it into the xyol
in petri dish
• The opercula is obtained from freshly killed fishes because the opercula in
formalin may become disvolored.

Relationship between the growth and opercula
bone
• Measurement from the origin to each succeeding annulus can be
made along a imaginary line from its apical articulation to its
posterior margin .
• The origin of measurement is the Centre of articular apex and
imaginary line cut the various annular growth lines.

3.vertebra
• Aikawa and smith 1951
• There is concentric mark on the vertebral centra
• Ring is defined as the narrowest kind of concentric mark observed
and a band as wider concentric mark is a group of rings.
• These bands are thought to be annual in many fishes.

4.Fin Rays
• Cross sections of fin rays and spines have also been found useful in
age determination.
• Boiko 1950
• Deelder and Willimse 1973

Method
• Cut the fin ray from near the base exactly transversely
• Polish the plane of section using a smooth hone
• Dry fin at room temperature for few days
• Embed it upside down in a piece of plasticine attached to side
examine under a microscope
• Using a low power objective and suitable source of illumination
• Alternate light and dark ring may be seen depicting periods of
summer and winter growths respectively.

5.Scales
• 99 % bony fishes having cycloid and ctenoid scales used for age
determination

Structure of scales
• Ctenoid scales differ from cycloid scales in having ctenii ( small spines)
on the posterior margin.
• Ctenoid scales are usually found in spiny ray finned fishes
• Cycloid scales present in soft ray finned fishes
• Both has similar type of arrangement in bony fishes a typical scale
consist of outer bony striated layer gives it flexibility and elasticity
• The focus near the centre of scale is a small area which represent the
original scale of young fish
• Ridges or circulii are more or less concentric around the focus
represent the margin of which the scale is made up of.

Advantages
• Of all the hard structures scales are most trustworthy means of
estimating age and growth calculation
• Transparency of scales the ease of sampling them and minimal
damage to fish make them desirable to work with.
• Almost a huge amount of work has been done with scales during past
250 years .

Identification of annual marks
• The use of scale to identified growth depends on the formation of
growth rings called annuli.
• Its appearance is different in different species
• These are identified by change in external figure of scale

Identification characters
1. A zone of closely spaced ridges is followed by a zone of widely
spaced ridges
• Annulus is regarded to be the outer margin of closely spaced
ridges
• Closely spaced ridges showed slower growth
• While spaced ridges showed faster growth
2. A discontinuous ridge between two continuous ones is also
one of the criterion which identifies annual mark

3. Crossing over
One of the most important character which helps
identification of annual mark present on ctenoid scale formed
when cutting one or two ridges appear to cut across several
others and is usually seen on lateral side of scale more
prominently

• 4. In some species during spawning season erosion of scales provide a
guideline for the location of annulus
• 5. when growth rings are numerous and reading age is find to get the
evidence from the transverse radii present on the anterior region of the
scale e.g. Tenualosa ilisha

Irregularities
• Some abnormalities or facts which makes difficult to age readings.
 False annuli
 Overlapping annuli
 Skipped annuli
 Closely spaced annuli
 Fri or larval annulus
 Regenerated scales

• 1. False annuli
In many cases accessory growth checks of false annuli have been
reported in addition to true ones. They are sometimes difficult to
distinguish from true annuli and make age determination less
accurate. Van Oosten in 1957 attribute these accessory annuli to
growth cessation due to fluctuation of temperature, food, drought,
disease, injury, spawning, starvation etc.
2. Overlapping annuli
Growth in length through one growing season is very small thus the
annulus for any given year coincides in part with that of next. One is
likely to commit error by considering the second component of double
ring as false annuli

• 3.Skipped annuli
The position of the annulus for one year coincides with that of
preceding year e.g. the fish does not grow during one growing season .
4. Closely spaced annuli
Growth for any given season is small and two annuli are very closed
spaced separated by only few circulii. Without growth formation one is
liable to commit mistake in identifying the outer annulus as false
annuli.
5.Fry or larval annulus
In some fishes like Roach there appears an additional ring (the so called
fry or larval) very closed and inside the first annual ring. This may be
ascribed to the event of larva changing over from planktonic to benthic
food.

• 6. Regenerated scales
The most common irregularly encountered during the study of scales is
regenerated scale in which clear well defined focus is replaced by an
expanded central area without any circulii or mark.

Validity of annuli on scales as year marks
• The reliability of age and growth information from scales or other
hard parts of body must be checked before accepting it.
• This annuli may be regarded as year mark if,
a. There is regular increase in body size correlated with an increased
number of growth rings
b. Length frequency peaks of small fish should coincide with modal
length of corresponding age groups based on scale readings
c. Scale remain constant in number and identity throughout life
d. There is constant ratio between the annual increment in the radius
of scale and the annual increment in body length
e. The annulus is formed yearly at the same time each year

How to collect and cleans the scales
• Envelops are used to keep scales or for recording data
 Date of capture
 Name of fish
 Length
 Weight
 State of gonad
 Name of collector
 Type of gear used
Record

Key scales
• A key scale is the one which is taken from the same point on each fish
•Point
•The point is determined by count along lateral line
and then again count above and below the lateral line.

Method
to clean
scales
If it is spiny ray-finned fish then the scales are taken from the region of
the tip of pectoral fin
If it is soft ray-finned fish they are taken from the area between dorsal
fin and lateral line
About 10 scales from each fish are
enough and these can be removed by
the help of forceps
The scales are then temporarily stored in
envelopes
Scales may be cleaned by first soaking in
water and then by rubbing them
between two palms

Dry temporary mount
• Placed the scales between two slides
• The ends of slide may be pressed down with cellophane tape
• Permanent slides if desired can be made with euparol
• Wallin in 1957 has suggested that the appearance of scale can be
improved by treating with cobalt nitrate and ammonium sulphate by
staining with Alizarin red.
• Laborious method by stain

Reading scale
• Age determination is done by back calculations of lengths can be
accomplished most efficiently by projector or a binocular microscope
fitted with an ocular microscope.
• The age is ascertained by reading and counting annuli or year marks,
age, as determined from scales are usually expressed in Roman
numerals corresponding to number of annuli.
• So a fish having two annulus belonging to age group one annuli
belonging to group 2 and so on.

•Age group
•Age group refers to age in years while.
•Year class identifies the year of hatching

Year class can be determined by subtracting age from the
year of capture
• Example
• A fish of age group 3 captured in year 1970 belongings to 1967 year
class( the year of hatching).

Error
• Annulus formation dealing often extending from 2-3 months
• Particularly if fish sampling at time of annulus formation because
some fishes will have second annulus on the margin of scale while
others have not.
• So the same age fishes divided into two age groups

Body-scale relationship and back calculation
• From scales one can deduce the following information
1. The age of fish
2. Mean length of each age group
3. The past growth history by back calculation method

Scale-length relationship
• From the sample of mounted scale for each fish select a non-
regenerated scale or preferably use only key-scale
• With the help of binocular microscope fitted with ocular micrometer
measure the radius of scale which is from the centre of focus to the
margin of the scale
• Also record length the same radius from centre of each annulus

• The accuracy of back-calculation depends on body-scale length
relationship so that’s establish firstly
• When length of fish plotted on X against the radius on y
• Result
• (4 cases)
A. Linear with origin of zero
B. Linear but not passing through the zero but the graph cuts the
abscissa at some positive point
C. Curve linear
D. Graph may show a sigmoid curve

Relationship of body length and scale length

• Case A
• Scale growth is directly proportional to body growth i.e. isometric. The
length of fish corresponding to any length of scale can then by Leas
formula below

Case b
body length and scale length relationship is linear but not directly
proportional because graph cuts the abscissa at some positive scale
radius.

Case c
heterogenic relationship
curvilinear
• Log L =log K+n( log S)
Where L=length to be calculated
S=measurement of scale
K=intercept on the ordinate (in log units)
N=Slope

Case d
• If a sigmoid curve or S shaped curve is obtained by plotting the
empirical values of body length against scale radius . It may be
necessary to derive two formulae one to fit the data below the
inflection point. The formulae suggested for curve c is employed.

Lee phenomenon
• Character discrepancy called lees phenomenon
• This phenomenon shows that calculated lengths at the end of each
year of life decrease with each successive increase of age of the fish
upon which the calculation was based.

Causes for discrepancy
• Use of incorrect techniques of back calculation
• Differential natural mortality i.e. faster growing fish tend to mature
earlier than the slower growing individuals which thus constitute
most of the fish in the older age groups
• Selective sampling i.e. gears such as gill nets are selective and tend to
capture only the larger members of any given year class
• Non random sampling of the population e.g. if the sampling tends to
make more of the larger representatives the younger age groups

GROWTH
Types of
growth
1. Absolute growth
2. Relative growth
3. Instantaneous
growth
Factors affecting
growth factors
Walford growth
transformation
 Estimation of ultimate
length from Walford
plot
 Estimation of expected
length
Von bertalanffy
growth model
Length-weight
relationship

What is growth
• Growth is defined as increase in size over a time
• Increase in length or weight over a time
Growth
change in calories stored as somatic and reproductive
tissue
I=E+G
I=ingested food M=metabolism
E=excretion G=growth

Three processes encountered in energy
ingested
1. Variable amount of energy is excreted
2. Consuming during metabolism
3. Rest of stored as caloric growth

Factors affecting growth rate
• Temperature
• Photoperiod
• Dissolved oxygen
• Salinity
• Predation
• Parasitism
• State of maturity
• Maturation of gonads

Types of Growth
• Once the age is decided then the growth rate is described in number
of ways in terms of length or weight depends upon purposes of
study.
• 1. Absolute growth
• 2. Relative growth
• 3. Instantaneous growth

1.Absolute growth
• When average total size of fish is plotted against each age the curve
described absolute growth.
• This curve rises slowly at first with increasing slope followed by
decreasing slope during the remainder of curve
• The point at which at which growth curve changes from increasing to
a decreasing rate is known as inflection point
• In a slightly different manner the absolute growth rate may be
demonstrated by plotting the annual increments a differences
between successive total length against age this type of curve is
known as first differential of absolute growth curve.

• In graph the line A represent absolute growth plotted as regression of
length on age or average length of each age group
• The line B is drawn by plotting the annual increments or differences
between the successive length against age

Difference between absolute and relative growth
• The relative growth may also be demonstrated by either of the two
curves
• The line A exhibits the logarithm of lengths against age while line B is
drawn by plotting percentage yearly increase against time or age.
• When logarithm of length is plotted the curve rises sharply but the
slope continually declines throughout life.

• The main difference in absolute and relative treatment of growth
comes in early life since the slow growth of old age differs very little
weather regarded from absolute or relative point of view
• The absolute growth of young fish is slow in early part of life but it
increases constantly up to inflection point after which it gradually and
constantly decline whereas relative growth is most rapid at the
youngest ages and afterwards drop constantly like absolute growth as
seen from examples above absolute growth from age 1 to age 2 in 37
mm
• While from age 2-3 it is 34 mm

• Thus as regards absolute growth two values are practically the same
but from the view point of the relative growth there is a vast
difference
• On the first case it is 61.0 % while in later it is 35.0%
• The most important difference between the two view points
therefore relates to the rate of growth

3.Instantaneous growth
• Measure the growth rate of fish by measuring its length or weight at
regular intervals the difference over a given time being measure of its
growth.
• It is not able to compare the growth of two fishes

It is mostly used in connection with weights because
weights tend to increase exponentially.

• The determination of instantaneous growth rate help in ascertaining
both general and specific principles of growth of individual species
and of intra specific groups
• In our example instantaneous growth rate between age 2 and 3 is
• Growth characteristic

Walford growth transformation
• 1964
• Graphical representation of length at age n and along X axis with
length at age n+1 along Y-axis yielded a straight line for several
species of fish studied by him
• He regards this line as transformation of growth curves or WALFORD
PLOTT
•

Advantages
• The Walford plot is useful in number of ways
• It provides means for estimating growth parameters
• It can yield an estimate of ultimate length or weight
• it can be used to generate growth information to ages which may not
be readable from scales or other bones

Graphical representation
• Length at age n = 60 97 131 159 182 201 217
• Length at age n+1= 97 131 159 182 201 217 229

Estimation of ultimate length from Walford plot
• The length at which there is no further growth
• Called Length of infinity
• Denoted by Lα
• That is the theoretical length beyond which no further growth of
fishes occur
• Asymptotic or ultimate length is
Lα=intercept1-slope

• If intercept is n+1=48.40
• n=0.837
• Lα=297 mm

Estimation of expected length
• For used to unfold growth information to the future ages
• Which may not readable from scales or bony parts
• Thus if length at age 1 and 2are known but scales of fish beyond 3 years not
readable the same can be generated from walford plots the walford line may be
drawn taking two points taking the length at age 3 as the point on x axis drop a
perpendicular line on walford line and then on y axis the point on y axis provide
length at age 4 similarly the estimated length at age 4 may be taken as a point on
x axis and the expected length at age 5 may be read on y axis

Van bertalanffy model
• Fishery management
• Know the growth rates of fishes
 The fish grows towards some theoretical maximum
length or weight and the growth rate declines as the fish
reaches its ultimate length.

• Straight graph with a slope less than 1.0 Von Bnertalanffy fit the data
best
• Slope=e*
• Natural log with Walford plot with sign changed provide an estimate
of growth coefficient K
• The ultimate length or weight point is determined where growth
curve intersect at 45 degree through the zero point
Lα=intercept1-slope

• The 𝑡0 may be estimated from the growth equation after estimation
of K and Lα have been made

Methods to fitting bertalanffy growth
curve

Age and growth

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