Age and growth

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

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

2. Age and Growth

3. What is age Age is a duration of life

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

5. Methods of age determination Length frequency method Marking or known age method Interpretation of layers laid down in hard part of fishes Otoliths Opercula Vertebra Fin rays 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

6. Workers\scientist Rounsefell Everhart(!953) Lagler(1956) Ricker(1968)

7. 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.

8. 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.

9. 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 Sample should be composed of large number of individuals Sample should be good representative of all size and classes 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.

10. Disadvantage Method is not suitable for small samples 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. Many fish population particularly in tropical waters spawn throughout years distinct years classes are therefore difficult to be recognized in such settings One or more year classes may be poorly represented or may be absent.

11. 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.

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

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

14. 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.

15. 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.

16. 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

17. 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

18. Method Removed by pair of forceps Preserved in the mixture of 90 % alcohol and 10% glycerin. Rounsefell and Everhart recommend 3% solution of trisodium phosphate as preservative. To obtain translucent section it is mounted with Canada balsam on slide. 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. Transparent zones appears light while opaque zones are dark while examine in transmitted light.

19. 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 .

20. 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.

21. 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.

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

23. 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.

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

25. 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.

26. 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 .

27. 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

28. 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

29. 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

30. 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

31. 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 scal es

32. 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

33. 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.

34. 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.

35. 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, There is regular increase in body size correlated with an increased number of growth rings Length frequency peaks of small fish should coincide with modal length of corresponding age groups based on scale readings Scale remain constant in number and identity throughout life There is constant ratio between the annual increment in the radius of scale and the annual increment in body length The annulus is formed yearly at the same time each year

36. 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

37. 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.

38. 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 a nd 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

39. 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

40. 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.

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

42. 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).

43. 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

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

45. 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

46. Scale length relationship

47. 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) Linear with origin of zero Linear but not passing through the zero but the graph cuts the abscissa at some positive point Curve linear Graph may show a sigmoid curve

48. Relationship of body length and scale length

49. 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

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

51. 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

52. 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.

53. 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.

54. 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

55. GROWT H Types of growth Absolute growth Relative growth 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

56. 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

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

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

59. 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

60. FORMULAS

61. 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.

62. Graph

63. 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

64. 2. Relative growth

65. Graph

66. 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.

67. 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

68. 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

69. 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

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

71. 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

72. 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

73. 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

74. 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

75. Graphical representation

76. 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 L α =intercept\1-slope

77. If intercept is n+1=48.40 n=0.837 L α =297 mm

78. 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

79. 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.

80. 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 L α= intercept\1-slope

81. The may be estimated from the growth equation after estimation of K and L α have been made  

82. Methods to fitting bertalanffy growth curve

83. THANKS