NGUYEN XUAN LOC, Jan WOJCIECHOWSKI

Fish Biology

COMPARATIVE BIOLOGY OF FISH FROM GENUS DENTEX (SPARIDAE)
OF NORTH-WEST AFRICAN COAST

BIOLOGIA PORÓWNAWCZA RYB Z RODZAJU DENTEX (SPARIDAE)
WYSTĘPUJĄCYCH W REJONIE PÓŁNOCNO-ZACHODNIEJ AFRYKI

Institute of Exploitation of Sea Resources

The observations had been made during 1968-1970 on biology of fish of *Dentex* species of North-West African coast. The isolation of features differing these species permitted to form semantic arrangement for their denotation. The age and length composition, weight and rate of growth in relation to species, region of fishing and depth of their residing had also been investigated.

INTRODUCTION

Among many bottom appearing on fishing grounds of North-Western African coast dominate the *Sparidae* species. Their catches from the fishing grounds amount to 100 thousands tons per year. Majority of them are the fishes of *Dentex* species. By analysing Polish catches, it was determined that in North-West African shelf appear the following species belonging to the same family:

*Dentex macrophthalmus* (Bloch, 1971)

*Dentex maroccanus* Valenc., 1830

*Dentex congoensis* Poll, 1954

*Dentex filosus* Valenc., 1835

*Dentex polli* Roux, 1954

*Dentex canariensis* Steind., 1881

The same species were also encountered in region discussed by Loza-
mo Cabo (1970), Klimaj (1970), Maurin et al. (1970), Roux
(1957), Stepkina (1970) and Woźniak (1967).

In spite of considerable economic importance, biology of fish of *Dentex* species had not been yet well recognized.
The aim is made in this work to separate the features which differ the most important species of this genus and to analyse their length, age composition and growth.

## MATERIAL AND METHOD

The work is based on the investigations carried-out during 1968-1970 (Tab. 1). Subject to analysis was the material originating partly from catches of industrial fishing ships; 6 samples were taken during XII. 1968 till IX. 1969. This samples did not full represent the examined stocks because were composed of assorted fishes and did not include any young fishes. Majority of samples had been collected in period of 23. XII. 1969 till 3. III. 1970 during fishing voyage of trawler m/t "Murena".

Total length (1.t.) and body length was measured with accuracy up to 1 cm. The intermediate values were brought within the range of first decimal sign, viz.: length class 10.0 cm comprised the fishes from 10.0 cm to 10.9 cm. The fish *Dentex filosus* were classified by 2 cm length class. The 10 cm length class comprised in this case the fishes of 10.0 cm to 11.9 cm. Fish was weighed with accuracy up to 1 g.

The age was determined according to otoliths and scales taken from above lateral line. On otoliths of species from genus *Dentex* are clearly visible the opaque zones which form during intensive feeding and growth and the translucent zones, which from during growth inhibition. Both these zones jointly correspond to annual life of fish. The otoliths are clear for reading in II to VI age groups. Some about 3% of otoliths difficult for reading were rejected during the examinations. The scales were of little use for determination of age because did not possess clear rings of annual growth. Age readings were taken at convex non-polished side of otoliths within the light of binocular under small magnification.

To morphometric examinations were subjected the following species: *Dentex macrophthalmus*, *Dentex maroccanus*, *Dentex congoensis* i *Dentex canariensis*. The calculable features were analysed for all examined species. All morphometric measurements were made with accuracy up to 0.1 cm.

## RESULTS

According to observation, the following semantic arrangement was made for determination of *Dentex* species which appeared in catches:

A. Width of os lacrimale is below 6% of body length.

1. Large eye - above 12% of body length. At lower part of first gill arch 17 to 19 of gill rakers are found present. In lateral line 52-57 scales R.D. :XII-9-11; R.A. :III-8-9.

*Dentex macrophthalmus* (Bloch, 1971).

2. Medium size eye - ab. 10.4% of body length. Maximum height of body amounts to about 36.5% of total length (1.t.). On lower part of first fill arch noted 12-13 gill rakers. In lateral line 46-48 scales. R.D. :XII-10; R.A. :III-8

*Dentex congoensis* (Poll, 1954).
<caption>Table 1</caption>

Periods, regions and type of examinations

<table><thead><tr><th rowspan="2">Species</th><th rowspan="2">Sample No</th><th rowspan="2">Date of sample</th><th rowspan="2">Geogr.pos.</th><th colspan="5">Number of specimens examined</th></tr><tr><th>on length</th><th>on weight</th><th>on age</th><th>on growth rate</th><th>Morphometr. exam</th></tr></thead><tbody><tr><td rowspan="12">Dentex macrophthalmus</td><td>1</td><td>14.XII.1968</td><td>Cape Blanc</td><td>328</td><td>328</td><td>325</td><td>109</td><td>-</td></tr><tr><td>2</td><td>13.II.1969</td><td>19°56′N-16°38′W</td><td>107</td><td>107</td><td>107</td><td>52</td><td>-</td></tr><tr><td>3</td><td>8.III.1969</td><td>24°00′N-16°26′W</td><td>128</td><td>128</td><td>125</td><td>64</td><td>-</td></tr><tr><td>4</td><td>10.IV.1969</td><td>20°25′N-17°20′W</td><td>274</td><td>274</td><td>274</td><td>162</td><td>-</td></tr><tr><td>5</td><td>12.V.1969</td><td>22°30′N-17°10′W</td><td>623</td><td>623</td><td>608</td><td>319</td><td>-</td></tr><tr><td>6</td><td>18.IX.1969</td><td>21°32′N-17°39′W</td><td>362</td><td>362</td><td>350</td><td>146</td><td>-</td></tr><tr><td>7</td><td>23-31.XII.1969</td><td>17°40′N-19°07′W</td><td>4805</td><td>487</td><td>474</td><td>172</td><td>-</td></tr><tr><td>8</td><td>1-23.I.1970</td><td>16°09′N-19°05′N</td><td>9719</td><td>965</td><td>915</td><td>288</td><td>81</td></tr><tr><td>9</td><td>1-28.II.1970</td><td>15°50′N-18°40′N</td><td>2765</td><td>345</td><td>332</td><td>53</td><td>-</td></tr><tr><td>10</td><td>1-9.II.1970</td><td>13°30′N-14°50′N</td><td>1407</td><td>315</td><td>305</td><td>161</td><td>-</td></tr><tr><td>11</td><td>1-3.III.1970</td><td>17°40′N-17°50′N</td><td>1625</td><td>292</td><td>286</td><td>34</td><td>-</td></tr><tr><td rowspan="5">Dentex macrocaenus</td><td>12</td><td>23-31.XII.1969</td><td>17°40′N-19°07′N</td><td>2305</td><td>493</td><td>488</td><td>101</td><td>-</td></tr><tr><td>13</td><td>1-23.I.1970</td><td>16°09′N-19°08′N</td><td>1758</td><td>382</td><td>378</td><td>57</td><td>40</td></tr><tr><td>14</td><td>1-9.II.1970</td><td>13°30′N-14°50′N</td><td>1620</td><td>284</td><td>273</td><td>58</td><td>-</td></tr><tr><td>15</td><td>1-28.II.1970</td><td>15°50′N-18°41′N</td><td>404</td><td>138</td><td>123</td><td>15</td><td>-</td></tr><tr><td>16</td><td>1-3.III.1970</td><td>17°40′N-17°50′N</td><td>325</td><td>55</td><td>45</td><td>-</td><td>-</td></tr><tr><td>Dentex filos</td><td>17</td><td>23.XII.1969<br>3.III.1970</td><td>15°50′N-19°07′N</td><td>314</td><td>247</td><td>240</td><td>114</td><td>25</td></tr><tr><td>Dentex polli</td><td>18</td><td>23.XII.1969<br>3.III.1970</td><td>15°50′N-19°07′N</td><td>857</td><td>191</td><td>185</td><td>105</td><td>35</td></tr><tr><td>Dentex canariensis</td><td>19</td><td>19.I.1970</td><td>18°09′N-16°23′W</td><td>41</td><td>41</td><td>39</td><td>-</td><td>25</td></tr><tr><td>Dentex congoensis</td><td>20</td><td>1-9.II.1970</td><td>13°30′N-14°50′W</td><td>580</td><td>332</td><td>320</td><td>103</td><td>35</td></tr><tr><td>Total</td><td></td><td></td><td></td><td>30374</td><td>6389</td><td>6192</td><td>2113</td><td>241</td></tr></tbody></table>
B. Width of os lacrimale - above 6% of body length.

1. Large head - about 38% of body length. Preorbital angle rounded. On lower part of first gill arch 9-10 of gill rakers. In lateral line 47-49 scales. R.D.:XII-10-11;R.A.:III-8.

<u>Dentex polli</u> (Roux, 1954).

2. Medium size head. Its length amounts to ab. 33-33,6% of body length (1.t.).

a) Max. height of body amounts to ab. 38.4% of body length (1.t.). On lower part of first gill arch present 11 gill rakers. In lateral line 49-50 scales. R.D.:XII-10;R.A.:III-8.

<u>Dentex maroccanus</u> (Valenc., 1830).

b) Max. height of body about 40% of length (1.t.). At lower part of first gill arch present 14-15 gill rakers. In lateral line present 60-61 scales R.D.:XII-10;R.A.:III-8. At young fish, the third or fourth fin spinner is elongated. This phenomenon disappears at older specimens. At the base of last soft fin rays of dorsal fin noted pink-violette or dark spot.

<u>Dentex canariensis</u> (Steind., 1881).

c) At lower part of first gill arch present 12 gill rakers. In lateral line present 54-60 scales. R.D.:XII-10;R.A.:III-8. Young specimens possess elongated two first fin spiners of dorsal fin. The elongations disappear at older species. At males in front part of body forms the hump.

<u>Dentex filosus</u> (Valenc., 1836).

As it appears from data presented from table 2, particular species of fish belonging to <u>Dentex</u> genus differ by numerous morphometric features. This is well seen after expressing the values in % of body length (1.t.). Particularly, this relates to size of head, diameter of eye, width of forehead and width of os lacrimale. Further features which differ these species, are: number of gill rakers at lower part of first gill arch; number of scales in lateral line; length of dorsal and anal fin. No distinct differences are noted in relation to height of body.

**Length.** The results of length measurement agree with observations of Domanevski et al. (1970,1971), Raźniewski (1964), Woźniak (1967). From length composition curves presented on Fig. 1 appears that subsequent peaks of these curves correspond in general to subsequent age groups determined acc. to number of rings on otoliths. This conforms the correctness of age reading. Exceptionally clear connection of length curve characteristic with number of rings on otoliths was determined at *Dentex macrophthalmus* and *Dentex maroccanus*. This relates to a less extent at *Dentex filosus* and *Dentex polli*.

Length composition of caught fishes was also changing in relation to annual season. Young specimens were encountered mainly above Cap Blanc (North of Cap Blanc). It was noted that average length of these fishes was increasing in proceeding from North towards South, to attain in highest values below (South of) Cap Vert. It seems that an abundance of food resources for small fish was the main cause for this phenomenon. In Cap Blanc
<table><caption>Morphometric features of various species of *Dentex genus* caught at Mauretania and Senegal shelf during 1970</caption><thead><tr><th rowspan="3">Measurements</th><th colspan="2">Dentex macropthalmus</th><th colspan="2">Dentex maroccanus</th><th colspan="2">Dentex congoensis</th><th colspan="2">Dentex polli</th></tr><tr><th colspan="2">1.t. 15-21.5 cm N=40</th><th colspan="2">1.t. 15-21 cm N=40</th><th colspan="2">1.t. 15-21 cm N=35</th><th colspan="2">1.t. 15-21 cm N=35</th></tr><tr><th>% 1.t.</th><th>♂</th><th>% 1.t.</th><th>♂</th><th>% 1.t.</th><th>♂</th><th>% 1.t.</th><th>♂</th></tr></thead><tbody><tr><td>Length of head</td><td>35.04</td><td>0.38</td><td>33.55</td><td>0.40</td><td>34.38</td><td>0.37</td><td>37.90</td><td>0.77</td></tr><tr><td>Dia. of eye</td><td>12.10</td><td>0.16</td><td>11.07</td><td>0.13</td><td>10.42</td><td>0.15</td><td>11.16</td><td>0.32</td></tr><tr><td>Width of forehead</td><td>9.02</td><td>0.22</td><td>9.82</td><td>0.13</td><td>10.48</td><td>0.16</td><td>10.14</td><td>0.51</td></tr><tr><td>Width of os lacrimale</td><td>4.98</td><td>0.11</td><td>7.06</td><td>0.11</td><td>5.76</td><td>0.28</td><td>8.38</td><td>0.13</td></tr><tr><td>Max. height of body</td><td>40.64</td><td>0.50</td><td>38.41</td><td>0.43</td><td>36.52</td><td>0.37</td><td>40.80</td><td>0.52</td></tr><tr><td>Min. height of body</td><td>10.45</td><td>0.15</td><td>11.14</td><td>0.17</td><td>10.35</td><td>0.12</td><td>11.70</td><td>0.17</td></tr><tr><td>Length of anal fin at base</td><td>18.23</td><td>0.85</td><td>18.32</td><td>0.25</td><td>17.52</td><td>0.30</td><td>17.80</td><td>0.45</td></tr><tr><td>Length of pelvic fins</td><td>33.26</td><td>0.51</td><td>32.22</td><td>0.37</td><td>29.81</td><td>0.30</td><td>34.13</td><td>0.53</td></tr></tbody></table>

♂ = standard deviation
<figure><img src="image_1.png" /><figcaption>Fig. 1. Age and Length composition of particular Species from genus *Dentex*</figcaption></figure>
shelf the resources were richer than in Cap Vert shelf (Anonymus, 1970, Longhurst, 1959) and therefore more young specimens were encountered here.

The length and, at the same time, the age of caught fishes of *Dentex* genus depended also on fishing depth. Within limits of 100-170 m, while increasing the fishing depth, the length of *Dentex macrophthalmus* is increasing and the length of *Dentex maroccanus* is decreasing. This permits for practical conclusion that *Dentex maroccanus* resides in more shallow waters while *Dentex macrophthalmus* resides in deeper layers of water. Out observations on bathymetric distribution of these species agree principally with the results of Domanevski et al. (1970, 1971), Klimaj (1970), Maurin et al. (1970), Raźniewski (1964) and Wysokiński (1971). Only Woźniak (1967) forwarded the observations contrary to our investigations, i.e. with increase of depth upto 100 m, the sizes of *Dentex macrophthalmus* are decreasing and the sizes of *Dentex maroccanus* - increasing. This may be explained by the fact that present investigations were related to deeper waters of shelf and were made in period December to March, while the investigations of Woźniak (1967) were made at shallower waters during May-August.

Young fish of *Dentex* resides in shallow waters and with growth moves on to deeper waters (Domanevski et al. (1970, 1971), Stepkina (1970).

Our observations proved that for this region may appear various length and age groups of *Dentex* species. This may be conditioned by various period of spawning and by food composition of these fishes.

No distinct differences were noted in relation to length of males and females.

No exact data is available on changes of length composition of *Dentex* during recent years. The existing materials deal with this problem fragmentarily only. Out of comparison of our results with works of Domanevsky et al. (1970, 1971), Raźniewski (1964) and Woźniak (1967) is apparent that the average length of these fishes is decreasing in last fishing years.

Age. To new age groups were considered the fishes after 1.January. Exception was made only in December 1969 when for limit date was assumed 1.December; this was aimed to unify the method of age group classification for whole material caught during 23.XII.1969 to 3.III.1970.

According our observations ascertained that at majority of otoliths of examined species, the opaque rings were wider than translucent ones (Fig. 2,3). Some rings do not possess continuity on total edge of otolith, but these cases are not numerous. Additional difficulties in age determination of older specimen presented the narrow rings at the edges.

It appears from our observations, that translucent zones on otoliths of *Dentex macrophthalmus* are formed during late autumn and in winter (from November till April) i.e. during spawning period. The one-year specimens of individual length 8-12 cm caught in December 1969 had on otolith edge the translucent growth zone. Identical zone at otolith edge possessed also the majority of 2-7 year old specimens caught in autumn and winter. The oldest specimens possessed in the same time less distinct translucent and opaque zones at otolith edge.
<figure><img src="image_2.png" /><figcaption>Fig.2. Otoliths of particular species from genus *Dentex*</figcaption></figure>

1. *Dentex macrophthalmus*. Length 14 cm, weight 50 g, age 2 years, male caught 12.1.1970 on Cap Blanc shelf

2. *Dentex macrophthalmus*. Length 24 cm, weight 210 g, age 5 years, female caught 2.1.1970 on Cap Blanc shelf
<figure><img src="image_3.png" /><figcaption>Fig. 2. Otoliths of particular species from genus *Dentex*</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>3. *Dentex maroccanus*. Length 15 cm, weight 60 g, age 3 years, male caught 12.1.1970 on Cap Blanc shelf
4. *Dentex canariensis*. Length 24 cm, weight 155 g, age 3 years, female caught 19.1.1970 on Cap Blanc shelf</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 3. Otoliths of particular species from genus *Dentex*</figcaption></figure>

5. *Dentex polli*. Lenght 17 cm, weight 80 g, age 2 years, female caught 24. XII. 1969 on Cap Blanc shelf

6. *Dentex congoensis*. Length 15 cm, weight 50 g, age 4 years, male caught 8. II. 1970 on Cap Vert shelf
The observations showed that, at remaining species which spawn during summer months, the translucent zones at otoliths are formed also during winter and the opaque zones - during summer. Thus, the period of spawning has no influence on formation time of such zones at otoliths, but this is due to changes of hydrological conditions during the year and consequently the changes in feeding intensity.

It appears from drawing 1 that, oldest specimens encountered in catches, were 13 year old of *Dentex macrophthalmus*, 10 year old of *Dentex maroccanus*, 7 year old of *Dentex congoensis*, *Dentex filosus* and *Dentex polli* and 6 year old of *Dentex canariensis*.

<figure><img src="image_6.png" /><figcaption>Fig. 3. Otoliths of particular species from genus Dentex</figcaption></figure>

7. *Dentex filosus*. Length 38 cm, weight 700 g, age 3 years, female caught 14.1.1970 on Cap Blanc shelf

Rate of growth.
The determination of growth rate acc. to measurement of annual rings width on otoliths of fish required the knowledge of interrelation between length of fish and size of their otoliths rays. Depending on kind of such

interrelations, for further calculations may be used the straight (direct) proportional or adequate corrections must be made. Therefore, such interrelation was examined. Data relating to total length and to size of longer ray of otoliths were compared, and thus the following species were examined: 455 pcs of *Dentex macrophthalmus*, 247 pcs of *Dentex maroccanus*, 114 pcs of *Dentex congoensis*, 124 pcs of *Dentex filosus* and 105 pcs of *Dentex polli*. This permitted to determine the interrelation which in respect of longer ray of otolith is expressed by the following equations:

$r = 0,2190 L + 0,1960$ for *Dentex macrophthalmus*

$r = 0,2067 L + 0,1666$ for *Dentex maroccanus*

$r = 0,2254 L + 0,0831$ for *Dentex congoensis*

$r = 0,1820 L + 0,1010$ for *Dentex filosus*

$r = 0,2115 L + 0,1480$ for *Dentex polli*

where: r - size of longer ray of otolith,

L - total length of fish.
<figure><img src="image_7.png" /><figcaption>Fig.4. Growth rate of fish of *Dentex* genus from Cap Blanc shelf</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig.5. Growth rate of fish of *Dentex* genus from Cap Vert Shelf</figcaption></figure>
<caption>Table 3</caption>

Von Bertalanffy's equation coefficients calculated for *Dentex* genus from N.W. African coast

<table><thead><tr><th rowspan="2">Shelf</th><th rowspan="2">Species</th><th colspan="3">Coefficients</th></tr><tr><th>l</th><th>in cm</th><th>k</th></tr></thead><tbody><tr><td rowspan="4">Cap Blanc</td><td>D. macrophthalmus</td><td>37.5</td><td>- 1.320</td><td>0.162</td></tr><tr><td>D. maroccanus</td><td>34.3</td><td>- 0.490</td><td>0.180</td></tr><tr><td>D. filosus</td><td>107.0</td><td>- 0.600</td><td>0.124</td></tr><tr><td>D. polli</td><td>46.4</td><td>- 0.280</td><td>0.220</td></tr><tr><td rowspan="3">Cap Vert.</td><td>D. macrophthalmus</td><td>39.0</td><td>- 0.880</td><td>0.160</td></tr><tr><td>D. maroccanus</td><td>32.5</td><td>- 0.620</td><td>0.180</td></tr><tr><td>D. congoensis</td><td>30.3</td><td>- 0.807</td><td>0.160</td></tr></tbody></table>

The interrelations presented graphically possess the characteristics approximated to straight line crossing through centre of coordinates arrangement. This justifies the application of direct proportional for growth back readings.

Presented in table 3 are the coefficients of growth rate of examined species calculated by equations of von Bertalanffy. On bases of such coefficients, the theoretical rate of growth of these fishes was calculated (Fig.4,5).

It is apparent from comparison of growth rate that the examined species attain very good increase in growth of length during first year of life. Gradual inhibition of growth rate occurs in following years. It was noted in relation to 1-5 year of age *Dentex macrophthalmus* and *Dentex maroccanus* of Cap Vert shelf that their rate of growth was

<figure><img src="image_9.png" /></figure>

1. *Dentex macrophthalmus* 4. *Dentex polli*

2. *Dentex maroccanus* 5. *Dentex filosus*

3. *Dentex congoensis*

<caption>Fig.6. Length-weight relationship of fishes from genus *Dentex*</caption>
<caption>Table 4</caption>

Average weights of species of *Dentex* genus from N.W. African coast (in g)

<table><thead><tr><th>Length (l.t.)<br>in cm</th><th>Dentex<br>macro-<br>phthal.</th><th>Dentex<br>marocca-<br>nus</th><th>Dentex<br>filosus</th><th>Dentex<br>polli</th><th>Dentex<br>cana-<br>riensis</th><th>Dentex<br>congo-<br>ensis</th></tr></thead><tbody><tr><td>8</td><td>15</td><td>16</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>9</td><td>19</td><td>19</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>10</td><td>24</td><td>23</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>11</td><td>32</td><td>26</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>12</td><td>37</td><td>32</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>13</td><td>47</td><td>44</td><td>-</td><td>-</td><td>-</td><td>42</td></tr><tr><td>14</td><td>56</td><td>52</td><td>-</td><td>50</td><td>-</td><td>56</td></tr><tr><td>15</td><td>67</td><td>64</td><td>-</td><td>65</td><td>-</td><td>63</td></tr><tr><td>16</td><td>78</td><td>74</td><td>-</td><td>75</td><td>-</td><td>73</td></tr><tr><td>17</td><td>94</td><td>87</td><td>84</td><td>91</td><td>-</td><td>86</td></tr><tr><td>18</td><td>111</td><td>106</td><td>107</td><td>106</td><td>-</td><td>101</td></tr><tr><td>19</td><td>128</td><td>126</td><td>115</td><td>120</td><td>-</td><td>114</td></tr><tr><td>20</td><td>141</td><td>148</td><td>126</td><td>136</td><td>-</td><td>130</td></tr><tr><td>21</td><td>160</td><td>175</td><td>137</td><td>148</td><td>-</td><td>151</td></tr><tr><td>22</td><td>180</td><td>198</td><td>157</td><td>171</td><td>170</td><td>182</td></tr><tr><td>23</td><td>200</td><td>-</td><td>182</td><td>191</td><td>186</td><td>-</td></tr><tr><td>24</td><td>225</td><td>-</td><td>206</td><td>223</td><td>221</td><td>-</td></tr><tr><td>25</td><td>260</td><td>-</td><td>232</td><td>260</td><td>230</td><td>-</td></tr><tr><td>26</td><td>292</td><td>-</td><td>253</td><td>300</td><td>255</td><td>-</td></tr><tr><td>27</td><td>328</td><td>-</td><td>282</td><td>344</td><td>-</td><td>-</td></tr><tr><td>28</td><td>366</td><td>-</td><td>305</td><td>384</td><td>-</td><td>-</td></tr><tr><td>29</td><td>410</td><td>-</td><td>331</td><td>420</td><td>-</td><td>-</td></tr><tr><td>30</td><td>453</td><td>-</td><td>356</td><td>451</td><td>-</td><td>-</td></tr><tr><td>31</td><td>-</td><td>-</td><td>384</td><td>490</td><td>-</td><td>-</td></tr><tr><td>32</td><td>-</td><td>-</td><td>428</td><td>-</td><td>-</td><td>-</td></tr><tr><td>33</td><td>-</td><td>-</td><td>473</td><td>-</td><td>-</td><td>-</td></tr><tr><td>34</td><td>-</td><td>-</td><td>554</td><td>-</td><td>-</td><td>-</td></tr><tr><td>35</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr></tbody></table>
smaller in comparison to Cap Blanc shelf. Older specimens of both species demonstrated approximately equal rate of growth for both regions.

It appears from Table 4 that for the same length of specimens, the weights of *Dentex macrophthalmus* and *Dentex maroccanus* are distinctly higher than at remaining species. The interrelation between length and weight of the examined species were analysed and the following equations were obtained:

$$W = 0.01010 L^{2.98} \text{ for } \underline{\underline{\text{Dentex macrophthalmus}}}$$

$$W = 0.01569 L^{3.06} \text{ for } \underline{\underline{\text{Dentex maroccanus}}}$$

$$W = 0.01430 L^{3.08} \text{ for } \underline{\underline{\text{Dentex congoensis}}}$$

$$W = 0.01479 L^{3.0} \text{ for } \underline{\underline{\text{Dentex filosus}}}$$

$$W = 0.01419 L^{3.04} \text{ for } \underline{\underline{\text{Dentex polli}}}$$

where: W - weight of fish (in g),

L - length of fish (l.t.) in cm.

These interrelations are presented graphically on Fig. 6.

## CONCLUSIONS

1. The fish belonging to *Dentex* genus differ by numerous morphometric features. This was exploited in elaboration of semantic arrangement for their denotation.

2. The length and age of these depend on region and depths of their residing.

3. The age of these fishes determined from otoliths agrees with the same obtained acc. to Petersen's method.

4. Expressed graphically interrelation between length of fish (l.t.) and size of longer otolith ray possesses the characteristics aproximated to straight line passing through the centre of coordinates arrangement.

5. Rate of growth of fish from *Dentex* genus depends on its age and region of residing and it is not the same at all species examined.

## REFERENCES

* Anonymus, 1970: Sprawozdanie z rejsu M/T „Wieczno" na łowiska szelfu Północno-Zachodniej Afryki (24.I.-19.III.1970). [Relation from the cruise of M.T. "Wieczno" on the grounds of N.W. Africa in the period 24.I.-19.III.1970]. - Morski Instytut Rybacki, Gdynia.

* Domaneveski, L.N., Stepkina, M.V., Tkačenko, V. A., 1970: Nekotoryje osobennosti rosta u Dentex macrophthalmus Bloch i Sardinella aurita Val. v vostočnoj časti Centralnoj Atlantiki. - Voprosy Ichiologii, 10, 5/64/:861-869.

* Domanevsky, L.N., Stepkina, M.V., 1971: Osobennosti biologii bošeglazogo zubana Dentex macrophthalmus Bloch rajona Centralno-Vostocnoj Atlantiki. - Voprosy Ichiologii, 11, 3(68):438-446.
Klimaj, A., 1970: Fishing yield and species composition of trawl catches of M.T. "Ramada" on the fishing grounds on the shelf off Mauretania and Senegal in 1967. ICES, Rapports et Procés-verbaux des Réunions. 159: 254-260.

Longhurst, A.R., 1959: Benthos Densities off Tropical West Africa. ICES. Journal du Conseil, XXV, 1:21-28.

Lozano Cabo, F., 1970: Caractéristiques zoogéographiques de la faune ichthyologique des côtes des Îles Canaries, du Maroc, du Sahara espagnol et de la Mauritanie avec une étude spéciale des poissons côtiers. ICES. Rapports et Procés-verbaux des Réunions, 159:152-164.

Maurin, C., Lozano Cabo, F., Bonnet, M., 1970: In-ventaire faunistique des principales espècies ichthyologiques fréquentant les côtes nord-ouest africaines. ICES. Rapports et Procés-verbaux des Réunions, 159:15-21.

Raźniewski, J., 1964: Charakterystyka połowów dennych u wybrzeży Mauretanii na podstawie rejsu M.T. "Sejno" w roku 1963. [Characteristic of bottom trawl catches of M.T. "Sejno" in the Mauritania waters in 1963]. MIR, Gdynia. Studia i Materiały, 2 B.

Roux, Ch., Collignon, J., Rossignol, M., 1957: Mol-lusques, Crustaces, Poissons marins des côtes d'A.E.F. Office de la Recherche Scientifique et Technique Outre-Mer. Libraire Larousse. Paris: 196-199.

Stepkina, M.V., 1970: Sparovyje Severo-Zapadnogo poberežja Afriki. Rybnoe Chozjajstvo. Moscow. 6:8-10.

Woźniak, St., 1967: Rozmieszczenie ryb praźmowatych (Sparidae) na szelfie Afryki Północno-Zachodniej (w okresie maj-sierpień 1963 r.). [The distribution of Sparidae over the shelf of North-Western Africa) in the period may-august 1963]. Prace MIR, Gdynia, 14./A:7-26.

Wysokiński, A., 1971: Pionowe rozmieszczenie ryb przemysłowych na łowiskach Północno-Zachodniej Afryki (rejon Cap Blanc). [Vertical distribution of commercial fish in fishing grounds off North-West Africa Region of Cap Blanc)]. Prace MIR, Gdynia, 16/A:67-84.

BIOLOGIA PORÓWNAWCZA RYB Z RODZAJU DENTEX SPARIDAE
WYSTĘPUJĄCYCH W REJONIE PÓŁNOCNO-ZACHODNIEJ AFRYKI

Streszczenie

W latach 1968-1970 w czasie rejsu na łowiska znajdujące się w rejonie Północno-Zachodniej Afryki oraz w oparciu o materiały dostarczone do kraju przez statki przemysłowe dokonano obserwacji nad różnicami morfometrycznymi oraz długością, wiekiem i tempem wzrostu ryb z rodzaju Dentex (Sparidae).

Stwierdzono, że poszczególne gatunki tych ryb różnią się wieloma cechami morfometrycznymi. Uwidocznia się to po wyrażeniu tych danych w %: dłu-
gości ciała (1. t.), Na podstawie tych różnic ułożono klucz do oznaczania gatunków rodzaju *Dentex*.

Długość, wiek i wzrost tych gatunków zależą od rejonu ich występowania. Stwierdzono, że na wysokości przyłąka Cap Blanc znajdują one bardziej sprzyjające warunki do ich rozwoju w porównaniu z rejonem w pobliżu Przyłąka Zielonego (Cap Vert).

Ogólnie biorąc, są to ryby o stosunkowo krótkim cyklu życiowym. Najstarszymi osobnikami jakie spotykano w polowach były 13-latki. Dominowały 2- i 3-latki.

Wiek tych ryb można odczytać z otolitów, na których wyraźnie widoczne są strefy przeźroczyste i matowe.

Stwierdzono, że strefy przeźroczyste powstają w okresie późnej jesieni i w zimie. Związane to jest z rocznym cyklem zmian warunków hydrologicznych w tym rejonie oraz ze zmianami intensywności odżywiania się tych ryb.

Obserwacje nad batymetrycznym rozmieszczeniem wykazały, że w granicach 100-170 m wraz ze zwiększeniem się głębokości wzrasta długość powiwanego *Dentex macrophthalmus* a maleje długość *Dentex maroccanus*.

## СРАВНИТЕЛЬНАЯ БИОЛОГИЯ РЫБ РОДА DENTEX СЕМЕЙСТВА SPARIDAЕ РАЙОНА СЕВЕРО-ЗАПАДНОЙ АФРИКИ

### Резюме

В 1968-1970 годах, во время рейса в рыболовные районы Атлантики у северо-западной Африки, а также на основе материалов доставленных промышленными суднами в страну, изучали морфологические различия а также длину, возраст и темп роста рыб рода *Dentex* сем *Sparidae*.

Установлено, что отдельные виды этих рыб отличаются многими морфологическими признаками. Это становится особенно заметным после выражения данных в % от общей длины тела. На основе этих различий составлено определитель для рыб рода *Dentex*. Длина, возраст и рост рыб этих видов зависят от района их обитания. Установлено, что на высоте мыса Cap Blanc находят они более благоприятные условия развития по сравнении с районом вблизи Мыса Зеленого (Cap Vert).

Обобщая, рыбы эти характеризуются относительно коротким жизненным циклом. Самые взрослые, встречаемые в уловах особи были 13-летнего возраста. Преобладали 2 и 3-летние особи. Возраст изучали при помощи отолитов, на которых четко видны прозрачные и матовые зоны. Установлено, что прозрачные зоны розникают в период поздней осени и зимой. Это связано с годичным циклом изменений гидрологических условий в этом районе, а также с изменениями интенсивности поиска пищи этими рюами.
Наблюдения за батиметрической локализацией показали, что в пределах 100-170 м, по мере нарастания глубины, растет длина вылавливаемого Dentex macropthalmus а уменьшается длина Dentex maroccanus.

Received 10.VI.1972

Address:

Mgr Jan Wojciechowski
Instytut Eksploatacji Zasobów Morza AP
Szczecin, ul. Kazimierza Królewicza 4
Polska - Poland