Fisheries Research 22 (1995) 255-264

Age, growth and mortality of damselfish (Chromis chromis L. ) in the eastern middle Adriatic

Jakov DulEiC, Miro KraljeviC Institute ofoceanography and Fisheries - Split, Set. I, MeStroviCa 63, P.O. Box SOO, 58000 Split,

Croatia

Accepted 2 I June 1994

Abstract

Age, growth and mortality were analysed for damselfish 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, L,= 142.0 ( 1 -exp( -0.26( t+0.30) ). Weight increased allometrically for both males (b=3.12) and females (b = 3.08) during the spawning season. Total and natural mortality were found to be Z= 1.07 years-’ and M=0.72 years-‘. The exploitation ratio, E=0.33, revealed un- defished stock conditions in the studied area.

Keywords: Age distribution; Chromis chromis; Growth, fish; Mortality

1. Introduction

The damselfish, Chromic chromis (Linnaeus, 1758), is a small fish found in shoals in mid-water above or near rocky reefs or above sea-grass (Posidonia) meadows at depths ranging from 3 to35 m. It occurs in the Mediterranean and from Portugal southwards to Angola (Quignard and Pras, 1986). Although it is common in the Adriatic, it is of no commercial value along the Croatian Adriatic coast (except on some islands in the middle Adriatic, i.e. Volta, Lastovo, KorEula and Hvar:, where it is much appreciated) (Grub%& 1982).

Published information on its biology and ecoiogy is limited. Abel ( 1961) re- ported on the ethology of damselfish in the Mediterranean Sea. Saldanha ( 1966) presented data on morphological differences between juveniles along the Coast de Sesimbra (Portugal). Contini and Donato ( 1973 ) stated that the reproduc- tive cycle of damselfish is between July and September, but their observations

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256 J. Dulc’ic, M. Kraljevit /Fisheries Research 22 (1995) 255-264

were based on laboratory results only. The social organization and reproductive behaviour of this species from the Azores were investigated by Mapstone and Wood ( 1975). Arruda ( 1977) found some morphological differences between specimens from the Mediterranean and those from the Azores and islands around Madeira, while Duka and Shevchenko ( 1980) reported some essential differ- ences in morphology and nutrition between damsellish in the Mediterranean (Lampedusa) and the Black Sea.

The aim of the present study was to give information on age, growth and mor- tality of damsellish from the Adriatic Sea, since no information is currently avail- able on annulus formation, growth and mortality rates.

2. Materials and methods

Damselfish samples were collected at the stations shown in Fig. 1 (A, Hvar channel; B, the island of Vis; C, the island of Trstenik, near the island of KorEula) by beach seine, 4 mm (for individuals between 40 and 55 mm) and 22 mm mesh- size stretched. Sampling took place in May, June and July 1992, during the spawning season of damselfish.

Total length was measured to the nearest 0.1 mm and body weight to the near- est 0.01 g. The gonads were examined to determine sex and reproductive state. Maturity stage was determined according to Nikolsky’s scale ( 1976): Stage I, young individuals which have never spawned, II, the swelling process in the cav- ity of the gonad is complete, gonads are very small, eggs are not visible to the

Fig. 1. Map of three sampling points (0 ) in the eastern middle Adriatic sea Island of Vis; C, Island of Trstenik) .

(A, Hvar channel; B,

J. DulfiC, M. KraljeviC /Fisheries Research 22 (1995) 255-264 251

Table 1 Parameters of the regression ( W=aL.*) between total length (L,, cm) and gross weight ( W g) for damselfish (females, males and sexes combined)

Sex a b SE. (6) n r2 r

Females 0.0172 3.08 0.035 759 0.9986 0.999 1 Males 0.0138 3.12 0.049 471 0.9997 0.9997 Sexes combined 0.0164 3.10 0.038 1230 0.999 1 0.9994

S.E.( b), standard error of b. n, number of fish.

naked eye; III, ripening-eggs visible to the naked eye, the gonad increases in weight very rapidly, testes change from transparent to pale rose colour; IV, ripeness-ga- metes ripe, gonads have reached their maximum weight but the gametes do not yet run out when light pressure is applied; V, reproduction gametes run out on the application of light pressure to the thorax, the weight of the gonad rapidly decreases from the start to the finish of the spawning process; VI, spent gametes extruded and cavity of gonad swollen, gonad has the appearance of any empty sac (usually with a few eggs remaining in females, or sperms in males). Sex can also be determined by macroscopic differences between males and females: fe- males have a long ovipositor. Age classification was based on scales taken from the left side of the body, beneath the tip of the pectoral fin. Scales taken from each fish were cleaned in 5% sodium peroxide and viewed using a binocular mi- croscope (Reichert ) at 40 x magnification.

The length-weight relationship was described by the equation

W=t2Lb

where W is weight, L is total length, b is the growth exponent or length-weight factor and a is a constant. The linear regression lines for males and females were tested for significance using analysis of variance (ANOVA). The program FIT (iterative method) (S. Regner, unpublished data, 1988) was used to estimate the growth parameters L,. K and to in the von Bertallanfy equation:

L,=L,( 1 -e-k(t-co))

where L, is the length at age t, L, is the ultimate length that an average fish would achieve if it continued to live and grow, K is the growth coefficient which deter- mines how fast the fish approaches L, and t,, is the hypothetical age for L, = 0.

We used the program ELEFAN II to estimate natural mortality (M) using es- timates of L,, K and the mean annual environmental temperature of the study area ( 16.9”C for O-35 m depth; L. Stojanoski, personal communication, 1993) based on Pauly’s ( I983 ) empirical equation and estimation of F= Z-M, where F is the fishing mortality and 2 is the total instantaneous mortality rate. The exploitation ratio was calculated by the equation E= F/Z.

258 J. DuEid, hf. KraljeviC /Fisheries Research 22 (I 995) 255-264

50 -

LO -

30-

E z _ .F

5 -

20 -

IO -

0 w =0.0138 L 3Y5 d

r2= 0.9997 n = 10 I471 1

. W =0(1172-L~~~~ 9

r 2 = 0.9986

n =101759)

I

11 1’8

IO M 30 LO 50 60 70 80 90 loo 110 120 130 WJ 150

Total length (mm)

Fig. 2. Length-weight relationship of damselfish Chromis chromis (males, 0; females, 0 ) .

3. Results

3.1. Length-weight relationship

The length of individuals ranged from 40 mm to 134 mm and the weight from 3.24 g to 40.2 1 g. Length-weight regressions were calculated separately for males, females and for the sexes combined (Table 1). The length-weight curves for both sexes are shown in Fig. 2.

The slopes of the total length-weight regressions, which do not differ signifi-

J. Dukit, M. KraljeviC /Fisheries Research 22 (1995) 255-264 259

Table 2 Results of reading scale rings of C. chromis from the eastern middle Adriatic sea

Age

1 2 3 4 5 6 7 8 9

Males - n 0

(mm)

6 44.0 15 65.4 3!) 84.8 58 97.2

12’1 104.7 130 114.6 73 121.3 22 126.7

7 129.5

Females Total

*SD n Et &SD n Et (mm) (mm)

2.0 5 42.2 1.6 11 43.2 2.8 29 63.3 2.2 44 64.2 3.9 98 82.0 3.2 137 83.9 5.0 105 96.0 6.0 163 97.0 3.4 184 102.0 3.6 305 106.4 3.5 190 112.5 3.7 320 114.4 2.9 100 120.8 2.3 173 121.3 I.0 44 126.4 1.5 66 126.5 1.5 4 129.0 2.0 11 129.2

Length range

(mm) fSD

2.0 40-45 4.4 59-69 3.8 69-90 5.8 88-102 3.9 96-106 4.5 106-l 18 2.5 117-125 1.3 126-129 1.8 127-134

Total 47 I 759 1230

Table 3 Von Bertalanffy growth parameters for damselfish from the eastern middle Adriatic sea

Sex L(mm) K to *SD +SE r2 r

Males 143.1 0.25 -0.5 0.102 0.0416 0.9986 0.9993 Females 145.2 0.23 -0.5 0.133 0.0544 0.9977 0.9989 Sexes combined 142.0 0.26 -0.3 0.093 0.0038 0.9978 0.9996

cantly between sexes (ANOVA, P-c 0.001 ), indicate the positive allometric na- ture of growth (b ranged between 3.08 and 3.12).

3.2. Age and growth

Scales were collected from 1230 individuals. The results of reading scale rings in male and female damselfish are given in Table 2.

The observed lengths of individuals assigned to each group were used to tit the Von Bertalanffy growth model. The parameters are presented in Table 3.

Von Bertalanffy’s growth curve for the sexes combined is shown in Fig. 3.

3.3. Mortality

The mortality for both sexes combined is presented in Fig. 4, and the results of mortality estimates for males, females and the sexes combined are summarized in Table 4.

The value of Z was a little higher for females than for males. Natural mortality, M, was higher for males (M=0.74) than females (M=0.71). The exploitation ratio E was ~0.50; it ranged between 0.30 and 0.34 depending on sex, and was

260 J. DulEic, M. KraljeviC /Fisheries Research 22 (1995) 255-264

L, = ,42.0(,_e-0.26(‘*a30~l r2 = 0.9918 n=9

J I I I

1 2 3 4 5 6 7 8 9

Age I years I

Fig. 3. Von Bertalanffy’s growth curves fitted to mean length at age values for damselfish, Chromis chromis, from the eastern middle Adriatic sea.

CATCH CURVE

In l%N/Ot 1 I _ In,

”

-4

I 0 I

1 3 5 I 9

t IAbsolute age years)

Fig. 4. Length-converted catch curves for damsel&h, Chromis chromis. Arrows indicate points used for the regression of the natural logarithm of n/df on age (t, years). n, number of fish per length class LI-L2 corresponding to age class f,-f2, dt=t,-t, and t= (t, +&)/2. Z, total instantaneous mortality.

J. DulEic, M. KraijeviC /Fisheries Research 22 (1995) 255-264 261

Table 4 Total instantaneous mortality (Z, years-‘), natural mortality (M), fishing mortality (F, years-’ ) and exploitation rate (E) for damselfish in the eastern middle Adriatic sea

Males Females Total

Z 1.06 1.08 1.07 M 0.74 0.71 0.72 F 0.32 0.37 0.35 E 0.30 0.34 0.33

higher for females. The values of E obtained indicated that the fishing pressure exerted on the damselfish in the area under study was rather light (underfished stock). In coastal fishery of Dalmatia (especially on islands in the eastern middle Adriatic - see Introduction) damselfish form a small but significant component of the coastal beach seine and gill net catch that is used as delicious food and as bait for lobsters. We have no new data on catch, but GrubigiC ( 1982) reported that it is around 30 tons per year.

4. Discussion

Equations of the length-weight relationship revealed that females were slightly heavier then males because the fish were caught during the spawning season. Gru- biSiC ( 1982) reported that the spawning season of damselfish in the Adriatic is between May and August, while in the Mediterranean it is in summer (Quignard and Pras, 1986). Contini and Donato ( 1973 ) stated that the reproductive period for C. chromic falls during the months between July and September when the temperatures vary between 24 ’ C and 26 o C, but they based their observations on laboratory results. The growth exponents of 3.12 and 3.08 estimated for males and females, respectively, show that growth is positively allometric (PC 0.001) (Table 1).

Significant changes in body form usually occur at or near sexual maturity for most teleosts. This positively allometric relationship refers to sexually mature individuals caught during the resting stage of the sexual cycle. Also, food (quan- tity, quality and size) has often been related to variations in population parame- ters. The damselfish feeds exclusively on zooplankton (mainly copepods) (Duka and Shevchenko, 1980, J. DulEiC, unpublished data, 1993 ) . Primary and second- ary production rates are highest in the channel area and open waters of the east- em middle Adriatic during spring and summer (Vueetic, 1975; Pucher-Petkovic and Marasovic, 1980). These facts indicate that the quantity of food available to damselfish is high during the spawning season. According to Duka and Shev- chenko ( 1980) this relationship for damselfish from the Mediterranean in the vicinity of Iampedusa) was W= 0.0 14 L * 945 (length range 6 1- 120 mm, weight range 3.0-27.0 g), implying that growth is isometric; for damsel&h from the Black Sea it was W=O.O19 L * 867 (length range 7 l-100 mm, weight range 6.0-

262 J. DulEic. hi. KraljeviC /Fisheries Research 22 (199s) 25S-264

17.7 g), implying that growth is negatively allometric during the spawning period (May-June). The authors explained these differences between growth exponents by the different ecological conditions in some parts of the Mediterranean and the Black Sea. Changes in fish shape, physiological changes, hydrological environ- mental conditions, different food availability during life and biological span, growth increment or break in growth can all affect the growth exponent (Frost, 1945 ). It was also established that the growth exponent changes with respect to the locality the fish inhabits, and also to its sex, length, age and gonad maturity (Ricker, 1975).

The damselfish, C. chromic, is a relatively long-lived species. The oldest male and female was estimated to be 9 years old. Since there are no available data on age and growth of adult damselfish, it was not possible to make any comparisons. On the basis of our investigations, we established that the mean total length of juveniles after one year’s growth is 43.2 mm. Bertram ( 1965) reports that C. chromic in the Mediterranean (the coastal waters of Malta) are approximately 35 mm long after one year’s growth. Mapstone and Wood ( 1975) established that juvenile C. chromis from the Azores (standard length 45-6 1 mm), collected from among rocks, were nearing the end of either their first or second year after hatch- ing. The same authors reported that male juveniles began to set up territories for nesting when 60-85 mm in standard length (length from the tip of the snout to the base of the caudal fin), probably at the beginning of their third year. It should be noted that our results are for total length while those of other authors are for standard length. The conversion factor (standard length to total length) is 1.3 (J. DulEiC, unpublished data, 1993 ), so after the necessary calculations, we can con- clude that the values of total length after the first, second and third year’s growth are similar.

Bertalanffy’s growth curve fitted the data very well, as shown by the correlation coefficients (r=0.9993 for males; r=0.9989 for females; r=0.9995 for the sexes combined). Estimates of K suggest that growth for male and female damselfish is similar, but males grow at a slightly faster rate (K= 0.25 ) than females (K= 0.23 ) . The values of L, (142.0 d $?, 143.1 d and 145.2 $? mm) are smaller than the maximum recorded total length (L,= 160 mm) in the same study area (the is- lands of SCedro and Jabuka) reported by GrubigiC ( 1959) and Soljan ( 1975). According to Carus ( 1893) and Dieuzeide et al. ( 1953), the recorded maximum length of damselfish in the Mediterranean was 120 mm. Tortonese ( 1975) re- ported a maximum recorded value of 150 mm for the same area. Banarescu ( 1964) gave the maximum length of damsellish in the Black Sea as 175 mm and Svetovidov ( 1964 ) gave it as 146 mm, but for the Atlantic (the Portugese coast ) it was given as 148 mm (Saldanha, 1966). C. chromis, a slow-growing species (K= 0.26 ), shows regional differences in growth which depend on the ecological conditions in the areas of investigation. Water temperature can directly affect fish growth by influencing the physiology of the fish ( Weatherley and Gill, 1987). However, water temperature is also directly related to rates of biological produc- tion and hence to food availability (Elizarov, 1965 ) and plankton species com- position (Colebrook, 1982)) both of which influence fish growth. The maximum length of damselfish in the Adriatic is significantly lower or higher than that re-

J. DulEiC, M. KraljeviC /Fisheries Research 22 (I 995) 255-264 263

ported for the Black Sea, the Mediterranean and the Atlantic. This difference may also be attributed to the differences in temperature and probably differences in trophic potential in each of the areas.

Pauly ( 1980) reviewed natural mortality rates for 174 fish stocks and modal mortality was 0.2-0.3 (Vetter, 1988 ) . The natural mortality of damselfish in the area of study ranged between 0.7 1 and 0.74, depending on sex (Table 4), indi- cating that the damselfish is characterized by relatively high natural mortality. We presume that the main reason for such a high natural mortality in damselfish is predation. Damselfish have been found in the stomachs of Thunnus thynnus (Morovic, 196 1, 197 1) as well as in the stomachs of Scorpaena scrofa (Soljan and Karlovac, 1932 ) and Scorpaena porcus (Pallaoro and Jardas, 199 1) . These predators were all found in our area of study (%tpanoviC and Jardas, 1989), a fact which indicates that predation is probably a decisive factor in controlling variations in damselfish population parameters in the eastern middle Adriatic Sea.

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