review article UDC 597.3/.5:519.16(262.3-H) 639.2.01(497.5) 
AC E AN D GROWT H STUDIES O N FiSHES IN CROATIAN FISHERIES SCIENCE 
jakov DULCJC 
Institute of Oceanography and Fisheries, BR-21000 Split, P.O. Box 500 
ABSTRACT 
Age arid growth studies of fish species are one of the main analytical models to analyze the dynamics of exploited fish populations. In this study the author reviews the published data on age and growth parameters of some fish species in the Eastern Adriatic. Scales and otoliths were the main calcified tissues employed for age determination, while fin rays were scarcely used. Age and growth were determined for 17 fish species, which makes 
14% of 120 commercially interesting species. According to presented results we can conclude that there is still much work to be done in age and growth determination of commercially interesting fish species. 
Ke y words : age, growth, studies, Croatian fisheries 
INTRODUCTION AG E AN D GROWT H STUDIE S 
The demography of living organisms constitutes the The study of growth means basically the determina­research object of the popuiation dynamics. Since tion of the body size as a function of age. Therefore all changes in the number of individuals and the age stock assessment methods work essentially with age structure of a population result from interactions be-composition data. In temperate waters, such as the tween the biology of the species and the biotic and Adriatic Sea, can usually be obtained through the abiotic environments, the population dynamics can be counting of year rings on hard parts such as scales and fully considered a branch of ecology. As a quantitative otoliths. These rings are formed due to strong fluctua­discipline, the population dynamics uses mathematical tions in environmental conditions from summer to win-models as a main tool. Most population dynamics ter and vice versa. Von Bertallanfy growth model of models require previous work with biological models, or body length as a function of age is one of the common-include them as submodels, in particular the following est models for observing growth of most fish species. biological studies are of a great importance in ichthyol-The mathematical model is: L(t) - L „ (1 - ex p (-K (t-t 0)) , ogy: stock identification, length-weight relationship, where the parameters can to some extent be interpreted length-age relationship, sex ratio, proportion of mature biologically. L„ is interpreted as "the mean length of individuals and trophic relationship. very old (strictly: infinitely old) fish", it is also called the 
Biological studies of fish presently being carried out 
"asymptotic length". K is a "curvature parameter", which in the Mediterranean reflect the wide interest in growth 
determines how fast the fish approaches its L„,. The third being shown by scientists. However, the diversity of the 
parameter, t0, sometimes called "the initial condition pa-studied species, which ranges from pelagic to littoral, 
rameter", determines the point in time when the fish has and demersal habitats is noteworthy, and reflects the 
zero length. Biologically, this has no meaning, because multispecies nature of the Croatian fisheries. Species 
the growth begins at hatching when the larva already normally studied correspond to the exploited popula­
has a certain length, which may be called L(0) when we tions caught by a variety of fishing techniques: trawls, put t = 0 at the day of birth. îonglines, trammel nets, beach seine, etc. The growth of sardine Sardina pilchardus (Walbaum, 
in this paper I will attempt to present age and growth 1792) in the Eastern Adriatic was intensively studied studies in the Croatian fisheries science. (MuliniC, 1954; Sinovcii, 1983, 1986). The scales and otoliths were used for age determination. Calculated von 
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fakov DUlClC : AGE AND GROWTH STUDiES O N FISHES IN CROATIAN FISHERIES SCtiNCE, 233-236 
Bertalanffy's growth constants were: L„ = 20.5 cm; K = 0.46; tQ = -0-5; and sardine specimens sampled from commercial catches belonged from 1+ to 8+ age groups (Sinovčič, 1986). 
Morovič (1961) using otoliths and scales established age groups of several mugilids: Mugii cepbalus (otoliths ­3°, scales - 6°), Chelon iabrosus (otoliths - 5°, scales -5+), Liza aurata (otoliths- 4°), and Ltzasalien$(otoliths - 4°). 
Striped mullet, Mullus barbatus Linnaeus, 1758, was studied by Hai'dar (1970). Seven age groups were found (from 0° to 6°), using scales and otoliths, in the eastern Middle Adriatic. 
Hake, Merluccius merluccius (Linnaeus, 1758), is, like sardine, one of commercially most important fish species in the Adriatic Sea, and it was intensively studied (Županovič, 1961, 1968; Jardas, 1976; Županovič & jardas, 1986). Studying the age composition of hake from the jabuka Pit, using otoliths, showed highest presence of age groups 1 and 2 {Županovič & jardas, 1986), while the maximum age found was 9 years (Županovič, 1968). 
Growth parameters of the red pandora Pagellus erytbrinus (Linnaeus, 1758), obtained by graphic method, in the insular zone of the Middle Adriatic were: K - 0.201 and L„ = 37,7 cm. Scales were used for age 
determination  and  six  age  groups  were  obtained  
(Županovič & Rijavec, 1980).  
The growth of the Atlantic horse-mackerel  Tracburus  

trachurus (Linnaeus, 1758) was studied by Alegria-Her­nandez (1983, 1984). Calculated parameters of growth curve were: L^ = 37.55 cm; K = 0.22; t0 = -1.28. Age was determined by otoliths and specimens belonged to 0 to 9 age group. 
A study of biological characteristics of the grey mul­let Liza ramada (Risso, 1826) was carried out over a pe­riod of one year in Šibenik area. The following values of von Bertalanffy's growth parameters were estimated: = 52.5 cm, K = 0.25 and t0 - -0.1. Grey mullet attains maximum length at 12 years of age. Parameters were obatined by Ford-Walford method from mean grey mullet lengths (Sinovčič et al., 1986). 
Bogue, Boops boops (Linnaeus, 1758) is also a very important exploited species in the Croatian fisheries. Growth of the bogue from the Middle Adriatic was studied by Alegria-Hernandez (1989). Mean iength-at­age values were estimated from otoliths and analysis of polymodal length frequency distributions. Growth pat­terns were well described by von Bertajanffy growth equation. Growth parameters L„ = 338.89 mm; K = 0.167, and t0 = - 1.296 were calculated. 
The growth of the Adriatic anchovy, Engraulis encra­sicolus (Linnaeus, 1758), was studied by Sinovčič (1992). The following values of von Bertalanffy's growth parame­ters were estimated: L„ = 19.4 cm, K = 0.57 and tc = -0.5. The anchovy attains maximum length at 4 years of age. 
Tičina (1994) studied age of the tuna fish, Thunnus tbynnus Linnaeus 1758, in the eastern part of the Adriatic coast using the first spine of the first dorsal ray. He found that tuna between 0° and 4° age inhabit the Eastern Adriatic waters. 
Age and growth were analysed for damselfish, Chro­mis chromis (Linnaeus, 1758), collected in the eastern Middle Adriatic Sea. Growth in length, not showing significant differences between sexes, was expressed for the whole sample using the Bertalanffy equation: Lt ­
26 it +

142.0 (1 -e"0 -030i ) . Scales were collected from 1230 individuals. The damselfish is a relatively long-lived species. The oldest male and female were estimaed to be 9 years old (Dulčič & Kraljevič, 1995). 
Age composition of the striped sea bream, Lithog­nathus mormyrus (Linnaeus, 1758), was established us­ing the Bhattacharya method and additional observa­tions on annual rings on scales. Six age classes were obtained from Kaštela Bay (age 3: 21.7 cm, age 4: 26.5 cm, age 5: 28.4 cm, age 6: 30.3 cm, age 7: 31.6 cm, age 8: 33.4 cm) and from Mirna Bay (age 2.5: 19.4 cm, age 3.5: 24.1 cm, age 4.5: 26.9 cm; age 5.5: 29.4 cm, age 6.5: 31.3 cm, age 7.5: 32.8 cm). Von Bertalanffy's growth equation was fitted to these mean length-at-age data resulting in parameter values of L„ - 36.2 cm, K = 0.297, L, = -0.08 for KaSteia Bay, and L„ = 37.3 cm, K = 0.262, t0 = -0.38 for Mirna Bay (Kraljevič ef al.f 1995). 
Aspects concerning age and growth were analysed in the golden grey mullet Liza aurata (Risso, 1810) col­lected in Mirna Bay (eastern Adriatic). Mean length and age data derived using scale readings were used to esti­mate the growth parameters of the Von Sertalanffy equation. The theoretical maximum length was esti­mated to be L„ = 398 mm. The growth coefficient was K 
- 0.21 and tD = - 1,14. Seven age classes, ranging from 3+
 to 8+ and 11+ years, were defined by the scale read­ings (Kraljevič & Dulčič, 1996). 
Growth of the black sea bream Spondyliosoma can­tharus (Linnaeus, 1758) from the eastern Middle Adriatic was studied using data on the scales from 745 fish. The Von Bertalanffy growth equations was fitted on the basis of mean length-at-age data resulting in parameter values of L^ = 47.7 cm, K = 0.178 and t0 = -0.27, The black sea bream is a long-lived species. The oldest male was esti­mated to be 14 and female 9 years old (Dulčič & Kral­jevič, 1996). 
The age and growth of the gilt-head sea bream Sparus aurata Linnaeus, 1758 were determined from specimens collected in the Mima Estuary (northern Adriatic). Mean length at age data, as derived using scale readings, were used to estimate the growth pa­rameters of the von Bertalanffy equation: L^, = 59.8 cm, K - 0.15 and ^ = -1. 71. Twelve age classes ranging from 1 to 12 years were defined by scale readings (Kraljevič & Dulčič, 1997). Maximum age of 22 years was found for the gilt head sea bream in the Eastern Adriatic with parameters - 84.98 cm, K = 0.073 and tc = -2.823 (Kraljevič et al, 1998). 
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Regarding methods, it is worthwhile emphasizing the increasing number of studies using PC-computers with adequate softwares (ELEFAN, FISHPARM, FiSAT, etc.) to obtain data to improve understanding of recruitment and growth patterns. Scales and otoliths were the main cal­cified tissues employed for age determination, while fin rays were scarcely used. The daily growth rings in oto­liths of fish larvae, which have been employed for both age and growth determination and for calculating birth­date distribution, are increasingly used in the Mediterra­nean (Moraies-Nin, 1989, 1992; Palomera ei aI., 1988) and Adriatic studies - for sardine, anchovy and sprat lar­vae (Dulcic, 1995, 1997, 1998). in general, it is clear that three main subjects arise: the need to validate re­sults obtained, the problem of different stocks of the same species, and sampling limitations. 
VALIDATION METHODS 

Age and growth studies are basic for the analysis and management of fishery resources and for biological studies. The methods most commonly used are those involved in counting concentric rings in scales and otoliths. The growth rates of these rings are directly re­lated to time. The periodicity of the rings laid down in the calcified structures can be proved directly or indi­rectly. Direct methods involve rearing young fish and marking calcified structures. Rearing experiments are the most precise way to determine ring formation and periodicity, but cannot be applied to all species accord­ing to the otolith structure. The capture, marking of the fish and calcified tissue with an agent, such as tetracy­cline, and subsequent release have the advantage of allowing growth in natural conditions, but they are costly and limited to a few species. Indirect methods are based on the criteria of proportionality, seasonality, and back-calculation. The proportionality of fish growth and the calcified structure growth (otolith, scale, fin ray) are determined by means of regression methods. Seasonality of ring deposition can be analyzed by the monthly dis­tribution of margin type (opaque or hyaline). If the rings are measured, the evolution of the value of the last ring completion (R) can be used for numerical determination: 
R = R„x 100/ Rn„f 

where Rn = is thickness of the last-deposited in the margin, Rn_i = is the thickness of the previous ring. However, when comparing these values, the decreasing thickness of consecutive rings should be kept in mind. The back-calculation of lengths by age is generally per­formed using the Fraser-Lee equation (Duncan, 1980): 
SL j = a + (S L - a ) * R j / L R 

where SLj is the standard length at previous age i, a is the intercept of the regression line of standard length (SL) on otolith (or scale) radius (LR), and Rj is the i-th radius of the otolith. The back-calculated values should be close to the actual values obtained from recordings and should follow a Von Bertalanffy growth curve. Other methods must be developed in future based upon otolith composition, DNA/RNA ratios and lipofucsin analysis, since all the mentioned methods are already functioning in the world (Bennet et al., 1982; Bulow, 1987; Hill & Radtke, 1988). The presence of various stocks in the same area could also cause differences in growth rates and age composition of a species. Stocks are discrete groups of fish, which show little mixing with adjacent groups. An essential feature is that population parameters should remain constant over the distribution area of the stock. There is still much work to be done in fish stock differentiation and delimitation, but recent ad­vances in methodologies based on genetic analysts will bring an improvement to our knowledge and facilitate correct growth determination. One of the main prob­lems is sampling limitations. Correct sampling is funda­mental for age and growth studies, for it is necessary to sample the entire size range of the population. Sampling can be biased among the others by two main factors: equipment selectivity and unequal size (and age) distri­butions, for instance, bathymetric size distributions. The use of only juvenile fish for growth determination can give unrealistic growth parameters. 
ŠTUDIJ E O STAROST I IN RAST I RIB V HRVAŠK I iHTIOLOŠK I ZNANOST I 
Jakov DULČIČ 
inštitut za oceanografijo in ribištvo, HR-21000 Split, P.O. Box 500 
POVZETEK 
Študije o starosti in rasti ribjih vrst so ena glavnih analitičnih modelov za analizo dinamike izkoriščanih ribjih populacij. Avtor v tern članku ocenjuje že objavljene podatke o starostnih in razvojnih parametrih nekaterih ribjih vrst v vzhodnem Jadranu. Luske in otoliti so bila glavna kalcificirana tkiva, primerna za ugotavljanje starosti, medtem ko plavuti skorajda niso bile uporabljene. Starost in rast sta bili ugotovljeni za 17 ribjih vrst, kar je 14% od stodvajsetih komercialno zanimivih vrst Glede na predstavljene rezultate pa lahko le zaključimo, da bo na področju ugotavljanja starosti in rasti komercialno zanimivih rib treba opraviti še veliko dela. 
Ključne besede: starost, rast, študije, hrvaška ihtiološka znanost 
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