Some biological aspects of Solea elongata from the Shatt Al-Arab estuary, North West Arabian Gulf.

Aspects of the biology of 1086 Solea elongata from the Shatt Al-Arab Estuary, Northwest Arabian Gulf were described during for the period Jun. to Dec. 2000. The length frequency distribution of the whole sample exhibited unimodal distribution; one peak observed at length 90 mm indicates that catches were exclusively based mainly on one year-class individuals. S. elongata had not been caught during November. LengthWeight relationship was found to be: W= 2.6 x 10 L . Growth rate was estimated to reach the length 100-109 in 1.1 year. Feeding activity values ranged from 50 to 85 %, while the minimum feeding intensity ratio was 0.4 point/fish and the maximum 3.2 point/fish. Diet of S. elongata was exclusively on molluscs (bivalves, Bithynia sp.). INTRODUCTION The soles (Soleidae), a family, of flatfishes, widely distributed in the world, including 135 species in 28 genera both and fresh waters. The genus Solea is represented by 11 species and many soles are commerical species: the common sole, Solea solea, is disturbed in northern Europe and the Mediterranean (Froese and Pauly, 2006). Soleidae in the Arabian Gulf are represented by 6 species; Aseraggodes cyanecus, Pardachirus marmoratus, Solea elongate, Synaptura orientalis, Zebrias synapturoides and Zebrias quagga (Kuronuma and Abe, 1986). Mohamed et al. (2001) recorded four species of this family; Synaptura orientalis, Zebrias synapturoides, S. elongate and S. bleckeri in Iraqi marine waters. S. elongata Day, 1877 is a demersal fish distributed from western Indian Ocean (Red Sea and Arabian Gulf) to the west and east coast of India, Sri Lanka and China. Adults inhabit shallow sand and mud bottoms in coastal waters 226 A.R. M. Mohamed et al. -------------------------------------------------------------------------------------------------------------to a depth of 8 – 28 m (Menon, 1984). The total catch of S. elongate was 403.6 tons and formed 0.72% from the total fish production in Bangladesh waters during 1989-1990 (Ahmad, 2005). Hasan et al. (2005) caught S. elongate together with other 22 species of fishes from various parts of Indus delta, Pakistan. Agah, et al. (2007) recorded low methylmercury fraction in the smallest specimen of S. elongate (TL, 18-21cm) compared with other six species sampled by bottom trawl survey at Mogham and Lengeh ports located in the Hormozgan province, southern Arabian Gulf. Soleidae species are landed in small quantities in Iraq, as a by-catch species mixed with other flatfishes species, and none of these comprises a single species fishery. However, the highest catch rate of Soleidae species by trawling in Iraqi marine waters was 2.4 kg/h in April 1990 (Mohamed, 1993). Ali, et al. (1998) reported that the total landing of black sole Euryglossus (Synaptura) orientalis by marine artisinal fisheries in Iraq was 20.9 tons in 1990. Soleidae larvae (S. elongate and two unidentified species) were one of the most abundant fish larvae at the offshore stations, northwest Arabian Gulf during December 1990 as stated by Hussain and Ahmed (1995). The recruitment, distribution and abundance of S. elongata larvae were widely reported in Kuwait Bay, north Arabian Gulf (Dames and Moore, 1983, Houde et al., 1986, Wright, 1989, Grabe et al. 1992.). No published works were traced concerned the biology of S. elongata in the Arabian Gulf. The aim of the present work was to study the main aspects of the biology of S. elongata, namely length frequency distribution, length-weight relationship, growth and food nature, in the Shatt Al-Arab Estuary. MATERIALS AND METHODS Monthly samples of S. elongata were collected from the trawl catches of R.V ‘Behar’ of the Marine Science Centre, Basrah University as a bycatch of the general fish survey during 2000 at the Shatt Al-Arab Estuary, northwest Arabian Gulf. (Fig. 1). Collection of fish made using 20 x 1.5m trawl with a stretched mesh size of 1cm of the net and 3cm of the wings. The specimens were immediately preserved in crashed ice for subsequent analysis. The species was identified after Fischer and Bianchi (1984). The total length and the weight for each fish in the samples were recorded to the nearest mm and 0.1g, respectively, and then were classed into 1 cm categories to plot the length frequency distribution. The lengthweight relationship was obtained by fitting the equation: (LeCren, 1951) W = aL, where W= weight (g), L= total length (mm), and a and b are constants). The length cohort analysis (Jones, 1984) was applied to provide information on the growth rate of S. elongata. A value of ∞ L (Fischer and Biology of Solea elongata 227 ------------------------------------------------------------------------------------------------------------Bianchi, 1984, Menon, 1984) and the K value obtained was 0.40 (Jones, 1984). Stomachs were individually assigned a fullness index value (Ball, 1961). Percentage feeding activity of each monthly sample was calculated after Dipper et al. (1977) and mean monthly feeding intensity was estimated according to Gordon (1977). Index of relative importance, IRI, (Pinkas et al. (1971) was employed to assess the importance of each food item in the diet. Fig. 1: Map of the Shatt Al-Arab estuary, northwest Arabian Gulf, showing the sampling area (shaded). 228 A.R. M. Mohamed et al. ------------------------------------------------------------------------------------------------------------RESULTS Length Frequency Distributions A total of 1086 specimens of S. elongata were caught throughout the study period. The monthly length frequency distributions of the species are illustrated in Figure 2. The species was collected in every month except November. The smallest individual (45 mm) and the length(129 mm) were appeared in the catch in July.The length frequency distributions clearly show the small sizes of fish caught and exhibited one mode in all months. The length frequency distribution of the whole sample exhibited unimodal distribution, one peak observed at length 90 mm. The fish at length groups 80 to 100 mm formed 98.2% of the total catch. The main length group (90 mm) was dominant and representing 40.10% of the total number of endividuls and the second important length group was 80 mm forming 30.9% and length group 100m constituted 14.80% of the total catch. These were young-of-the-year settlers collected from their feeding ground in the Shatt Al-Arab Estuary. Growth The length–weight relationship of S. elongata was represented with the following equation: W= 2.6 x 10 L 3.285 (TL= 45-129mm, r2 = 0.99, n = 205) and (b) was statistically significant. The results of length cohort analysis of 1086 fish ranging from 45 to 129mm are given in Table (1). The growth curve of S. elongata is constructed by plotting the lengths against corresponding relative ages (Fig. 3). The species was grown to 95mm T.L in the end of the first year. Table 1. Data for length cohort analysis of S. elongata in the Shatt AlArab estuary. Relative age (year) t2 t1 No. of fish Length group (mm) 0.5 0.547 0.455 3 50-59 0.6 0.653 0.557 5 60-69 0.7 0.764 0.664 3 70-79 0.8 0.879 0.775 336 80-89 0.9 1.001 0.892 457 90-99 1.1 1.128 1.014 161 100-109 1.2 1.263 1.142 112 110-119 1.3 1.405 1.277 9 120-129 Biology of Solea elongata 229 ------------------------------------------------------------------------------------------------------------Fig. (2): Monthly length frequency distributions of S. elongata in the Shatt Al-Arab Estuary 0 10 20 30 40 50