SOME BIOLOGICAL ASPECTS OF HAMILTONII AND IN KHOR AL-ZUBAIR, NORTHWEST ARABIAN GULF

N. A. HussAiN AND T. S. ALI Marine Science Centre, University of Basrah, Basrah. Iraq,

ABSTRACT

Study on 826 specimens of T. hamiltonii (Gray) and 439 specimens of T. mystax (Bloch and Schneider) collected from Khor al-Zubair during the period from July 1983 to June 1984 has shown that the dominant length range for both the species is 15.0-19.9 cm, representing 62.7% of the total number of T. hamiltonii and 58% of that of T. mystax. Based on GST, both species have single, prolonged spawning, extending from December to April, with peaV in March.

Length-weight relationship and 'K' factor have been calculated for both species. The nature of food has proved that both are carnivorous, depending mainly on shrimp and remains. However, T. hamiltonii is the dominant species from September to December whereas T. mystax is dominant from Fe­ bruary to August. But the peak feeding for both the species is during September and December, and, according to the Morisita index (C), high competition exists between the two species.

INTRODUCTION are widely distributed throughout the Indian Ocean, the Ara­ bian sea and the Red sea (Kuronuma & Abe 1972). They contribute largely to the fishery industry of the Arabian -Gulf (Lamboeuf & Simmonds 1981). Of the six species of anchovies recorded from the Arabian Gulf (Relyea 1981), and T. mystax are among the common species caught in the coastal regions. Most of the previous studies on anchovies are mainly concerned with spawning period, maturation cycle and, to a less extent, with length-weight re­ lationship and food and feeding habits (Venkataraman 1956, Dharmamba 1959, Masurekar & Rege 1960, Shamsul-Hoda 1976, 1982, 1983). But, despite flie commercial importance of T. hamiltonii and T. mystax in the northern Arabian Gulf, no attention has so far been paid to the study of their biology. NEUROCRANIUM OF FLATFISH 151

REFERENCES DAS, M. 1981. Coastal water ichthyofauna of two districts (Cuttack and Bdasore) of Orissa with observation on the feeding and reproductive biology of some flatfishes. Ph.D. thesis, Calcutta University. DATTA, N. C. AND M. D««. 1984a. Cranial anatomy of some Indian Cynoglossids. A study in adaptation. Part^I: CHteology, Zool. Jb. Anal., 112: 33-42. DATTA, N. C. AND M. DAS. 1984b. Cranial anatomy of some Indian Cynoglossids. A study in adaptation. Par-II Myology, Zool. Jb. Anat., 112: 43-50. DoBBEN, W. H. VAN. 1937. Uber • <}en Kiefermechanismus der Knochenfische. Archs. neerl, Zool., 2: 1-72. KAPOOR, A. S. AND P. P. OJHA, 1973. The olfactory apparatus in the flatilsh Cyno­ glossus oligolepis. Trans. Amer. Micros. Soc., 92(2): 298-304. KYLE, H. M. 1923. The asymmetry, metamorphosis and origin of flatfishes. Phil. Trans. R. Soc. (B), 211: 75-129. MENON, A. G. K. 1977. A systematic monograph of the tongue soles of the genus Cyno­ glossus HAMILTON-BUCHANAN (Pisccs: CynogloSsidae). Smithson. Contrib. Zool, 238: 1-129. NELSON, E. M. 1963. A preparation of standard teleost study skull. Turtox News, 41: 72-74. OcHiAi, A. 1966. Studies on the comparative morphology and ecology of the Japanese soles. Spec. Rep. Misaki. mar. biol. inst. (Kyoto University), 3: 1-97. SAXENA, P. K. AND R. K. RASTOOI. 1968. The cranial nerves of the flat fish, Cynoglossus bilineatus. Annotnes Zool. Jap,, 41: 70-76. TAYLOR, W. R. 1967. An enzyme method for clearing and staining small vertebrates. Proc. V.S. natn. Mus., \22: 1-17. TRAQUAIR, R. H. 1865. On the asymmetry of the Pleuronectidae, as elucidated by an examination of the skeleton in the turbot, halibut and plaice. Trans. Linn. Soc. I^ndon, 25: 263-296. YAZDANI, G. M. 1969. Adaptation in the jaws of flatfish (Pleuronectriformes). J. Zool., London, 159: 181-222. BIOLOGICAL ASPECTS OF ANCHOVIES 153

MATERIAL AND METHODS

Fishes were collected duiriiig the period from July 1983 to June 1984 from Khor al-Zubair (Fig. 1), using four fixed giU nets of diflferent mesh sizes, 1.0, 1.5, 2.0 and 2.5 cm^., and classified after Al-Daham (1977). Specimen^ were analysed individually for total length (T.L.), weight (W) and gonad weight. Stomach contents were examined for food composition after Hynes (1950) and Windell (1968). Similarity of food items between the two specie$ was ascertained by the Morisita iiidex (Cx):

s XI Yi C X = 2 L s xi2 + I Yi^ where (s) is the total number of food items, (xi) is the proportion of food items in the stomach of T. hamiltonii and (Yi) the proportion of these items in the stomach of T. mystax. (i) represents % of the total points allotted.

3100

Jd'ao

3(fot

ARABIAN GULF

FIG. 1. The map of nortKern Arabian gulf showing the sampling area. 154 HUSSAIN AND ALI

RESULTS A total of 826 specimens of T. hamiltonii and 439 of T. mystax were collected during the sampling period.

Length-Frequency Distribution The distribution of length frequency for T. hamiltonii is represented in Fig 2a. The main size range, 15-19.9 cm, was predominant during the period from September to May, forming 62.7% of the total number. The second im­ portant size group was 20-24.9 cm, which appeared in samples from Septem­ ber to June with a peak in February. The size group 10-14.9 cm was dominant during the summer months, when the Juveniles < 10 cm also appeared in the samples.

FIG. 2. Length-frequency distribution of T. hamiltonii (above) and T. mystax (below).

The length-frequency distribution of T. mystax is shown in Fig. 2b. Here also the dominant length range was 15-19.9 cm, found during September to BIOLOGICAL ASPECTS OF ANCHOVIES 155

May, forming about 58% of the total number. The second important size group was 10-14.9 cm, dominating in the suminer months. The size group < 10 cm was absent round the year.

The Gonado-Somatic Index (GSI)

The GSI results (Fig. 3) have indicated that, for both the species, there was a prolonged spawning period, extending from December to April (reach­ ing the nutxwnnm in March).

4.^0 1..00 3.80 J>0 3i<.0 i20 3.00

?j60 ?M zao

^ wo O no

1,40

1.20

1.00 aeo

O.bO

0.1.0

0,20

Jul Au9. Sept Oct., Nov. Get, Jan F«t «or. Apr May JUn

FIG. 3 The gonado somatic index (GSI) of T. hamiltonii (unbroken line) and T. mystax (broken line).

Length-Weight Relationship Length-weight relationship for both species was calculated using the wbole Siample. The Results, shown in Fig. 4 and Fig. 5, are best represented by 156 HUSSAIN AND ALI the following equations:

r. hamiltonii W = 0.00275 L^'^^^

r. mystax W = 0.00309 L 3.264 The rate of change (n) of weight relative to length in the equation for r. hamiltonii was a little different from that of T. mystax, the rates being 3.286 and 3.264 respectively. This indicates that T. hamiltonii was marginally more robust than T. mystax of the same length and both species grew at a rate higher than that of cube total length.

w X •

1.1 • 0,9 •

1 Tl 17 n I' '^ f 7 1. log I. L^9 U FIG. 4. Length-weight relationship of FIG. 5, Length-weight relationship of T. hamiltonii. T. mystax.

The Relative Condition Factor (K) Calculated K values for T. hamiltonii and T. mystax are shown in Fig. 6. Two peaks were noticed for both species, the first at 14 cm (K = 1.111 for T. hamiltonii, K = 1.115 for T. mystax) and the second at 20 cm (K = 1.114 for T. hamiltonii, K = 1.120 for T. mystax), respectively representing the minimiun and maximimi maturation lengths.

Food and Feeding Habits For the study of food, the stomachs of 660 T. hamiltonii and 410 T. mystax were examined. The results of the stomach analysis, expressed by both points and occurrance methods, are shown in Table 1 and Table 2. Animal remains were the dominant food item of T. hamiltonii, forming 47.15% of the total points, whereas shrimps (Parapenaeus stylifera and Meta- penaeus ^affinis) constituted the most dominant food item of T. mystax, form­ ing 43.03% of the total points. BIOLOGECAL ASPECTS OF ANCHOVIES 157

Shrimps were the important food item of t. hamiltonii during the period from August to December and of T. mystax during August to January. Animal remains were of major importance during the period from February to July for

0 9 K> » tt « l< ^ 16 17 m-'tf X 21 22 23 X 25 FIG. 6. Variation of Condition factor (K) in relation to length (cm) in T. hamiltonii (unbroken line) and T. mystax (broken line).

both species. Fishes (Mugil spp. and Otolithes spp.) were the third important food item, forming 7.85% and 7.50%, respectively for T. ha­ miltonii and T. mystax, with two peaks, in October and in March. Crabs (Petrolisthes lamarckii, P. indicus and Macrophthalmus depressus) formed tiie fourth important food item and were found in 4.73% and 5.66% respectively of the T. hamiltonii and T. mystax examined, with a peak in April for the former and February for the latter. Molluscs (Dosinia laminata) were found only in less than 1% of both species,. Generally, the feeding intensity of bofli species was high during the period from September to January and decreased sharply during the summer months. The stomachs were empty in 2.6% of T. hamiltonii and 1.7% of T. mystax examined. (Tables 1 and 2). According to Morisita index (C x ), the similarity level of food items between the two species reached 0.99, indicating a maximum similarity in food components.

DISCUSSION Different species of Thryssa appear to mature when they are about the same size. The first maturation size for T. hamiltonii from Bombay waters is TABLE 1. Food analysis of T. hamiUonii (P : points; O : occurrence). 00

Months Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Total

No. of Fish examined 45 3 12 27 51 100 100 41 100 62 87 38 660 Total Points 249 30 181 332 649 1337 1412 310 1203 706 971 287 7707 % Empty stcnnachs 15.5 0 8.3 7.4 1.9 0 0 0 0 3.2 1.1 9.4 2.6

Food items: P % 48.20 43.34 8.85 21.98 14.48 29.83 49.29 43.87 64.09 63.60 70.65 60.63 47.15 Animal remains O % 76.3 100 45.4 72.0 68.0 44.0 78.0 41.4 86.0 83.3 84.8 75.8 c 7) > P % 28.52 46.66 59.66 29.51 71.03 65.92 47.81 18.70 16.37 17.56 17.10 27.87 38.23 Shrimp z o % 36.8 66.6 72.7 60.0 96.0 69.0 59.0 12.1 22.0 25.0 17.4 34.4 > p % 1.60 10.0 17.13 34.04 4.16 1.87 1.84 32.59 10 J1 6.37 8.44 8.02 7.85 Fish o % 2.6 33.3 18.1 44.0 6.0 2.0 3.0 12.1 14.0 3.3 6.9 13.7

p % 6.83 — 7.18 10.85 3.39 1.58 — 4.20 8.48 11.90 2.88 3.48 4.73 Crab o % 18.4 36.3 44.0 12.0 3.0 9.7 18.0 26.6 5.8 10.3

p % — — 1.10 0.30 0.15 0.22 0.21 0.54 0.25 0.57 0.41 — 0.30 Mollusca o % 9.0 4.0 2.0 1.0 3.0 2.4 2.0 1.6 2.3

p % 14.85 — 6.00 3.32 6.78 0.58 0.85 — 0.50 — 0.52 — 1.74 Detritus o % 34.2 — 36.3 16.0 44.0 1.0 2.0 — 1.0 — 1.1 —" TABLE 2. Food analysis of T. mystax (P : points; O : occurrence)

Month Jul. Aug. Sep. Oct. Nov. Etec. Jan. Feb. Mar. Apr. May Jun. Total

No. of Fish examined 8 6 11 24 28 63 47 22 64 71 48 18 410 Total Points 33 45 132 262 399 855 619 265 709 795 476 157 4747 % Empty stomachs - 37.5 0 18.2 0 0 0 0 0 0 0 0 ll.l 1.7 & S Food items: P % 54.55 48.89 15.91 18.32 15.03 9.12 27.30 54.33 51.34 70.57 78.15 63.06 40.98 Animal lentKims ' O % 80.0 100 55.5 54.1 64.2 25.3 53.1 68.1 76.5 87.3 85.4 87.5 ^ •0 P % 36.36 46.67 50.0 41.22 54.88 86.55 63.65 21.13 26.93 13.08 18.49 35.03 43.03 M Shrimp O O % 40.0 50.0 77.7 62.5 78.5 93.6 61.7 22.7 31.2 19.7 16.6 50.0 O •a P % _ 19.70 24.81 18.29 2.93 1.94 3.78 14.10 5.54 0.63 7.50 Fish 2>; O % — — 33.3 29.1 21.4 1.5 2.1 4.5 12.5 5.6 2.0 — § 9 % 9.09 4.44 7.57 9.22 5.26 1.40 1.94 20.76 4J8 10.31 2.73 1.91 5.66 Crab iu O % 20.0 16.6 44.4 33.3 14.2 4.7 10.6 27.2 9.37 21.1 4.1 6.2

P % 0.77 0.26 1.27 0.50 0.34 Mollusca 0 % — — — 4.1 3.51 — — — 4.6 1.4 — —

P % 6.82 14.96 6.28 5.17 1.98 2.49 Detritus o % — — 33.3 16.6 32.1 — 12.7 — 3.1 — — — 160 HUSSAIN AND AM reported to be 15 cm (Masurekar & Rege 1960); and for T. mystax from Cal­ cutta and Pakistani waters to be 14.5 cm (VeD^ataraman 1956) and 14 cm (Shamsul Hoda 1982, 1983) respectively. However, T. dussumieri from the Pakistani coast is reported to mature at 13 cm (Shamsul-Hoda 1976). In the present study the first maturation size for both species is 14 cm. In the present study, T. Hamiltonii and T. mystax are found to have the same pattern of spawning habit, characterized by a prolonged season and two peaks. Besides, the GSI results have clearly shown that, of these two spawning peaks, the first is during December-January and the second is during March- April. The same trend of spawning has been observed also by Venkataraman (1956), Dharmamba (1959) and Masurekar and Rege (1960). Al-Matar (1982) has collected the eggs and the larvae of Thryssa spp. during late spring and early summer in Kuwait waters, indicating that Thryssa spp. spawn during late winter and early spring in the northern Arabian Gulf. Our results have shown that the size group 10-14.9 cm dominates' the sairiples during the sum­ mer months, as has been observed by Shamsul-Hoda (1983). Monthly GSI and relative condition factor (K) have demonstrated that T. hamiltonii has a pattern of breeding time similar to that of T. mystax, sug­ gesting that r. hamiltonii and T. mystax breed at the same time of the year. This coincides with the reported increase in productivity of phytoplankton and zooplankton in the northern Arabian, Gulf (Abdul-Razzak 1984). Similar spawning periods have also been: observed for other commercial species in the northern Arabian Gulf (Hussain & Abdidlah 1977, Abu-Hakima 1984).

The values of (n) for both specjes have agreed with the general cubic |aw (LeCren 1951), and are close to what has been reported by Shamsul-Hoda (1983), but differ widely from: Venkataraman .(1956). This suggests that T. mystax of Khor al-Zubair has a growth pattetra similar to that of the Paki­ stani coast but different from that of Bay of Bengal. A detailed study of the food and feeding habits has shown that T. ha­ miltonii and T. mystax are carnivores, preying mainly upon shrimp and fish, This observation is in agreement with tl^t of Venkataraman (1956) but is in contradiction to the observation of Relyea (1981), who has contended that anchovies are planktonfeeders. A close correlation is seen between the major food items and their seasonal aljundance. As for instance, the fish feed inten­ sively on shrimps during the period from August to January, when the latter are at their highest abundance in Khor al-Zubair (FAOH^DP, .1980).

The decrease of feeding intensity of T. hamiltonii and T. mystax during summer could be related to high water temperature, which is then 25°C (Ali 1985). The same was noticed by Venkataraman (1956), too. The high value of Morisita index (C x = 0.99) indicates high feeding competition BIOLOGICAL ASPECTS OF ANCHOVIES 161

between the two species in Khor al-Zubair, though T. hamiltonii, as indicated by its having been twice as much as T. mystax in the collection, is far too domi­ nant. Relyea (1981) too has stated that T, hamiltonii is the more abundant species of Thryssa in Iraqi waters.

The abundance of mature sizes throughout the year indicates that the species are resident in Khor al-Zubair as has been concluded by Ali (1985). It is also apparent that T. hamiltonii and T. mystax are coastal species, as has been previously pointed out by Blegvad (1944). Al-Matar (1982) has stated that the larvae of Thryssa spp. are more abundant in Kuwait Bay than in the offshore waters of the northern Arabian Gulf. The results of this study thus indicate in general that Khor al-Zubau: is the feeding and spawning area of these two species.

ACKNOWLEDGEMENTS Our sincere thanks are to Dr. H. A. Ahmed for reading the manuscript and to Miss A. H. Shaker for preparing the drawings.

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AL-DAHAM, N. K. 1977. Fishes of Iraq and Arabian Gulf. Vol. 1, Al-Arshad Press. Baghdad, 456 p. Au, T. S. 1985. Preliminary Study oa the Nature of Bony Fish Assemblage in Khor al-Zubair. M.Sc. thesis. Univereity of Basrah, Iraq. 108 p. At-MATAR, S. 1982. Abundance and Distribution of Clupeidae and Engraulidae in Ku­ waiti Waters. KISR Ann. Res. Rep. (1982. 208-109. BLEGVAD, H. 1944. Fishes of Iranian Gulf. Danish Scientific Investigation in Iran. Copenhagen. 247 p. DHARMAMBA, M. 1959. Studies on the Maturation and Spawning Habits of Some Com­ mon Clupeoids of Lawson's Bay. Indian J. Fish. 6: 374-388. FAO|UNDP. 1980. Report to the Gqvernment of Kuwait on Shrimp Resources Evalua­ tion and Management. FAO|UTEN|KUW|003!KUW, 10 p. HussAiN, N. A. AND M. A. S. ABDULLAH. 1977. The Length-Weight Relationship, Spawn­ ing Season and Food Habits of Six Commercial Fishes in Kuwait Waters. Indian 1. Fish. 24: 181-194. HYNES, H. B. N. 1950. The Food of Freshwater Sticklebacks (Gasterasteus aculeatus and Pygosteus purtgitius) with a Review of Method used in Studies of the Food of Fishes. /. Atdm. Ecol. 19: 36-58. 162 HUSSAIN AND ALI

KuRONUMA, K. AND Y. ABE. 1972. Fishes of Kuwait. KISR. 123 pp. LUMBOEF, M. AND E. J. SiMMONDS. 1981. Acoustic Estimation of the Biomass of the Stocks of Small Pelagic Species in the Gulf and the Gulf of Oman. In: FAO. Pelagic Resources of the Gulf and the Gulf of Oman. FI: DP|RAB|71|278|11. 144 p. LECREN, E. D. 1951. The Length-Weight Relationship and Seasonal Cycle in Gonad Weight and Condition in the Perch (Pewa fluviatilii). Ibid. 20: 201-219. MASUREKAR, W. B. AND M. S. REOE. 1960. Observations on the Maturity and Spawning of Thrissocles hamiltonii (Gray) in Bombay Waters. /. mar. hiol. Ass. . 12: 17-23. RELYEA, K. 1981. Inshore Fishes of the Arabian Gulf. The Nat. Hist. Arabian Gulf. 149 p. SHAMSin.-HooA, S. M. 1976. Reproductive Biology and Length-Weight Relationship of Thryssa dussumieri. (Valenciennes) of the Pakistani Coast. /. mar. hiol. Ass. In­ dia. 18: 272-287. SHAMSUL-HODA, S. M. 1982. Maturation and Spawning of the Thryssa mystax in the northern Arabian Sea. Indian J. Fish. 29: 213-222. SHAMSUL-HODA, S. M. 1983. Some observations on the distribution, maturity stages and length-weight relationship of the anchovy Thryssa mystax in the northern Arabian Sea. Indian J. Fish. 30: 278-286 VENKATARAMAN, G. 19S6. Studies on some aspects of the Biology of the Common Anchovy, Thrissocles mystax (Bloch & Schneider). Indian J. fish. 3: 311-333. WiNDELL, T. J. 1968. Food Analysis and Rate of Digestion. In: Methods of Assess­ ment of Fish Production in Freshwaiers. IBP. Handbook No. 3, 348 p.