INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCE AND ENGINEERING (IJESE) Vol. 2: 83-92 http://www.pvamu.edu/texged Prairie View A&M University, Texas, USA

Feeding ecology of the round , Sardinella aurita (Family: ) in the Egyptian Mediterranean waters

Fedekar F. Madkour Marine Science Department, Faculty of Science, Port Said University, Egypt.

ARTICLE INFO ABSTRACT Article History The objective of the present study was to analyze the diet Received: Sept. 28, 2011 composition of the round sardinella, Sardinella aurita in the Accepted: Dec. 5, 2011 Egyptian Mediterranean off Port Said coast. Gut contents from 100 Available online: 2012 stomachs/season were examined. The gut fullness index was ______estimated and the percentage of empty stomachs was expressed as Key words: the vacuity index (VI). Diet composition was described using Sardinella aurita frequency of occurrence (%F) and numerical methods (%N). The Feeding habits diet of S. aurita consisted predominantly of (50.1%) Diet composition followed by phytoplankton (34%) and relatively small quantities of Mediterranean Sea detritus (15.9%). The major prey items were copepodes supplemented by diatoms followed by Protozoa and Chlorophyceae. The type and abundance of ingested prey were related to the plankton composition in the environment in order to determine prey-type selectivity. Diet composition of stomach proved that Sardinella aurita has a flexible adaptive strategy appeared obviously from adjusting its diet feeding habits to its specific requirements.

1. INTRODUCTION The study of the food and feeding habits of fish species remains a subject of continuous research, because it constitutes the basis for development of a successful fisheries management on fish capture and culture (Oronsaye and Nakpodia, 2005). Studies on diet composition are important in community ecology since the use of resources by organisms has a major influence on population interactions within a community (Mequilla and Campos, 2007). Studies of species resources requirements have been used in attempts to understand factors controlling the distribution and abundance of organisms (Ross, 1986). Analysis of stomach contents could provide useful information on positioning of the fishes in the food web of their environment and estimation of trophic levels (Pauly and Christensen, 2000; Post et al., 2000). In addition, the quality and quantity of food are among the most important exogenous factors directly affecting growth and indirectly, maturation and mortality of fish, thus being ultimately related to fitness (Wootton, 1990).

Sardine (Family: Clupeidae) is a mid-sized pelagic fish that represents one of the most important commercial fishery resources in the Egyptian Mediterranean Sea. The presence ______Corresponding author E-mail: [email protected] ISSN 2156-7549 2156-7549 © 2011 TEXGED Prairie View A&M University All rights reserved. 84 Fedekar F. Madkour Feeding ecology of the round sardinella, Sardinella aurita of in front of Nile Delta with high 2. MATERIAL AND METHODS abundance was related to the Nile flood. The 2.1 Environmental measures and plankton abundance and species composition of sampling sardine were greatly altered after the The study was conducted at Port Said construction of Aswan High Dam. Prior to coast (31º 29' N, 32º 33' E) which receives the damming of the Nile, the average fish brackish water inputs from Lake Manzalah catch reached to 35000 tons, where sardine (Figure 1). This lake is reported to be constituted around 50 % of this catch (18000 relatively eutrophic due to direct release of tons) (El-Zarka and Koura, 1965). After the sewage, industrial and agriculture wastes construction of AHD in 1964, the Egyptian into it (Hamza, 1985). Samples and Mediterranean fisheries declined to less than measurements were taken seasonally, one in one-fourth and sardine was the most affected each season: autumn (October 2009), winter fish which was declined drastically to 0.9% (January 2010), spring (April 2010) and of the total fish catch in 1971. This low level summer (July 2010). Temperature was was more or less retained till 1979, after measured using a mercury thermometer, which the sardine catch again increased salinity using a refractometer and pH by a reaching 31.7% of the total catch (Hamza, digital pH meter. Transparency was 2006). According to GAFRD (2007), it was measured using a Secchi disc. Dissolved raised to about 52% of the average total oxygen was determined by Winkler's method catch during the period 1997-2007. (Strickland and Parsons, 1972). Plankton Round sardinella, S. aurita samples were taken by nets of 30 and 100 Valenciennes, 1847, is considered as an μm mesh size for phytoplankton and abundant species of the sardine catch which zooplankton, respectively and then preserved together with Sardina pilchardus, and other in 4% formalin solution immediately. The species make up about 60% of the total fish plankton, phyto-and zooplankton, were production in Port Said landing sites identified to the lowest possible genus and (Mehanna et al., 2008). In the Egyptian counted although convenient higher Mediterranean waters, the S. aurita spawning groupings have been partially adopted for period runs from June to September, with its convenience of presentation. One way peak in late July to early August, when water ANOVA was performed on environmental temperature reaches the yearly maximum parameters to evaluate seasonal variations (El-Rashidy, 1987). S. aurita being a between them using software program SPSS commercially important fish needs special V. 17. attention and the study of its food and 2.2 Fish collection and stomach sampling feeding is important. Several studies have Samples of Sardinella aurita were been conducted on its fisheries and biology obtained seasonally from the fishermen (Rifaat, 1960; El- Maghraby, 1960; Hashem catches using purse seine net at landing sites and Faltas, 1979; Faltas, 1983 and Mehanna of Port-Said. Fish samples were chilled in et al., 2008) but only one on its feeding iced blocks immediately before being habits in Alexandria (Abdel Aziz and transported to laboratory for analysis. Total Gharib, 2007). The aim of the present work length of each specimen to the nearest was to determine the feeding ecology of S. centimeter was taken from the tip of the head aurita by studying seasonal feeding habits, to the tip of the tail, using a Vernier caliper. diet composition and selectivity as a function Specimens were dissected and the alimentary of prey availability. Also to provide tracts were removed by section at the point, information on the abundance of natural food where the stomach entered the abdominal needed by S. aurita at the Egyptian coasts off cavity and immediately before the anus. Both Port Said. Changes in diet composition the pyloric and cardiac stomachs were cut through the different growing stages were open and the main bolus of contents discussed. removed. The contents were then placed into Fedekar F. Madkour Feeding ecology of the round sardinella, Sardinella aurita 85 a 5 ml vial and any remaining contents were prominent body part were identified and washed in with 4% formalin solution. The counted. Fragmented body parts like gut contents were agitated to break up the carapaces, spines, segments, and legs were bolus into an even mixture and examined not included in the analysis and were under an inverted microscope. Only classified as a digested material. specimens with complete structures or with a

Fig.1: Map showing the trawling area in front of Port Said Fishing Harbor.

2.3 Food analysis containing food (%F). In the numerical Gut contents from 100 stomachs/season method, the number of each food item was were examined. The intensity of feeding expressed as the percentage to the total (fullness index) was estimated on a scale of number of food items found in the stomachs 0–4 (0 = empty; 1 = 25% full; 2 = 50% full; (%N). 3 = 75% full; 4 = completely full) as described by Pillay (1952). The percentage 3. RESULTS of empty stomachs to the total number of 3.1 Environmental variables and plankton examined stomachs was expressed as the availability vacuity index (VI). Diet composition was Seasonal fluctuations of hydrobiological described using frequency of occurrence and characters off Port Said waters are shown in numerical methods as described by Hyslop Table (1). There were significant seasonal (1980) and Costal et al. (1992). In the variations in temperature, salinity and water frequency of occurrence method, the transparency, while seasonal fluctuations in occurrence of food items was expressed as dissolved oxygen and pH readings were the percentage of stomachs with a certain insignificant (ANOVA, P>0.05). Densities of food item to the total number of stomachs plankton communities showed bimodal 86 Fedekar F. Madkour Feeding ecology of the round sardinella, Sardinella aurita annual cycles with different peaks duration zooplankton were subjectively categorized as for phytoplankton and zooplankton. The (Calanoida, Cyclopoida and more pronounced peaks occurred in winter Harpacticoida), Cladocera, Protozoa, fish (162498 individual/l) for phytoplankton, and eggs and larvae, and others (Chaetognatha, in summer (10923 individual/m3) for larvae of decapods, cirripedes, molluscs and zooplankton. Diatoms appeared as the echinoderms). Copepods were the most predominant component of phytoplankton, important zooplankton group in the contributing numerically 71% of the total investigated area, constituting an annual phytoplankton population throughout the average of 58.4 % of the total zooplankton study period, with an annual average of during the period of study, with a main peak 49570 individual/l. Cyanophyceae and of 7209 individual/m in summer. Although Chlorophyceae came in the second order, the density during winter was giving approximately close annual averages comparatively low (2923 individual/ m3) in (8237 and 7134 individual/l, respectively). comparison to the other seasons, it The most dominant phytoplankton species represented about 78% of the total were Cyclotella meneghiniana, Thalassiosira zooplankton in this season. Centropages, sp., Nitzschia closterium, Synedra pulchella, Paracalanus, Acartia, Oithona and Anabaena sp., Scenedesmus dimorphus and Euterpina were the main genera as Prorocentrum micans. The recorded zooplankton biomass builders.

Table 1: Environmental variables, phytoplankton (individual/l) and zooplankton (individual/ m3) densities at Port Said during autumn 2009-summer 2010. Autumn Winter Spring Summer Temperature (ºC) 21.3 16.2 24.2 28.6 Salinity (‰) 36.6 35.1 37.7 39.1 Secchi depth (cm) 160 130 230 250 Oxygen (mg/l) 6.9 7.1 5.4 5.9 pH 8.2 8.0 8.0 8.3 Total phytoplankton 71128 162498 32994 12539 Diatoms 57614 120249 17157 3260 Cyanophyceae 7824 19499 4620 1003 Chlorophyceae 4268 14625 7258 2383 Dinoflagellates 1422 8125 3959 5893 Total zooplankton 6315 3748 8638 10923 Copepods 3284 2923 3887 7209 Cladocera 708 75 501 1584 Protozoa 145 262 397 568 Fish eggs and larvae 126 157 268 426 Others 2052 330 3585 1136

3.2 Stomach fullness activity in spring with the highest percentage Out of 400 specimens of Sardinella of completely full stomachs (30%). aurita examined, 109 (27.3%) had empty 3.3 Seasonal diet composition and stomachs while 79 specimens (19.8%) had selectivity completely full stomachs. The percentage of The diet of S. aurita consisted empty stomachs varied with season as shown predominantly of zooplankton, which in Figure (2). The greatest number of empty accounted for 50.1% of the annual average stomachs was found in summer, giving the stomach content, followed by phytoplankton highest vacuity index (VI= 63%) while there (34%) and relatively small quantities of were no empty stomachs in spring. detritus/unidentifiable material (15.9%). Consequently, feeding intensity of S. aurita Zooplankton food items could be varied seasonally, giving high rate of feeding differentiated into four categories as follows: 1) copepods, mainly calanoids and Fedekar F. Madkour Feeding ecology of the round sardinella, Sardinella aurita 87 cyclopoids, comprised about 37.5%; 2) (comprised collectively about 3.1%). Protozoa, mainly tintinnids and foraminifera; Partially digested and digested food, such as 3) Cladocera; and 4) fish eggs and larvae fragmented carapaces, legs and antennae of (Figure 3). Phytoplankton food items zooplankton, were also present but were not consisted of diatoms (25%), Chlorophyceae used in the diet analysis. (5.9%), Cyanophyceae and dinoflagellates

Fig. 2: Sardinella aurita from Egyptian Mediterranean off Port Said, 2009-2010. Seasonal variation of feeding intensity, (0 = empty; 1 = 25% full; 2 = 50% full; 3 = 75% full; 4 = completely full).

Fig. 3: S. aurita from Egyptian Mediterranean off Port Said, 2009-2010. Percentage of annual average of diet composition items.

According to frequency of occurrence Chlorophyceae in the diet of the fish was in method, the major prey items were copepods autumn (25%) while Protozoa were most supplemented by diatoms followed by frequent in spring (21%). There was only Protozoa and Chlorophyceae (Figure 4). The low percentage of the remaining food items percentage frequency of each prey item that were irregularly found in the stomach varied seasonally, with copepods being the contents of S. aurita. main prey item in the diet all the year except The average seasonal numbers of in autumn ranging between 91% to 32% of different main food items following the the total food items. Diatoms were the most numerical analysis reflected that displayed common in autumn (75%), and declined to by frequency method giving a consistent be the second common food item for the presence of copepods, diatoms and other seasons. The highest occurrence of Chlorophyceae in the diet of S. aurita 88 Fedekar F. Madkour Feeding ecology of the round sardinella, Sardinella aurita

(Figure 5). Copepods particularly calanoids, Of diatoms, the centric forms particularly showed the highest percent contribution to Cyclotella, Thalassiosira and Coscinodiscus the diet of S. aurita in terms of number with constituted the most important diet of S. the highest value in summer (53.2%). aurita followed by pennates (Synedra, Diatoms and Chlorophyceae recorded the Nitzschia and Navicula). Of other highest value in autumn (34.9% and 11.9%, phytoplankton groups, Scenedesmus, respectively) while displayed relatively close Anabaena and Spirulina were usually percentage in other seasons with abundance represented by a few individuals in each of diatoms. A large number of phytoplankton stomach. genera were consumed by S. aurita.

Fig. 4: S. aurita from Egyptian Mediterranean off Port Said, 2009-2010. Seasonal variation of food items based on percentage frequency of occurrence as a function of total length (TL, cm).

Fig. 5: S. aurita from Egyptian Mediterranean off Port Said, 2009-2010. Seasonal variation of food items based on percentage contribution of each food item to the diet as a function of total length (TL, cm).

3.4 Feeding variation with fish size aurita. In fish size <11 cm TL, the diet The total length of collected specimens composition was characterized by the ranged between 8 to 16 cm. In order to predominance of plant origin items evaluate variations in food habits as a (phytoplankton) which collectively did not function of size, the specimens were divided exceed 45.7%, with a great quantity of into eight classes with 1cm length intervals. diatoms, giving the highest percentage (40%) As shown in Figure (6), copepods and in size class 6-7cm. Starting from size class diatoms were found in all size groups of S. 11cm onwards, changes in diet composition Fedekar F. Madkour Feeding ecology of the round sardinella, Sardinella aurita 89 were observed, where the food items of 16cm. The length classes of 8-12 cm TL origin began to increase with were characterized by the occurrence of high increasing fish size. Copepods constituted percentage of detritus (up to 25%) which the main animal origin items forming the decreased as fish length increased. highest percentage (86.3 %) in size class15-

Fig. 6: S. aurita from Egyptian Mediterranean off Port Said, 2009-2010. Variation of food items based on percentage contribution of each food item to the diet for the different size classes.

4. DISCUSSION 2007; Shalloof and Khalifa, 2009). In This study provides more insights into contrast to our result, Tsikliras et al. (2005) the feeding habits of Sardinella aurita at Port found that the index VI was low in the Said, which was observed from samples spawning season and they explained their obtained during the four seasons of 2009- finding as fish need more energy input in 2010. S. aurita was infrequently found to spawning season to meet the requirements of abstain from feeding, thus food was present reproduction. in most of the examined guts (72.7%). The Diet composition of S. aurita revealed relatively low percentage of occurrence of that they usually feed at the surface as empty stomach was due to the availability of indicated by their planktonic stomach food material for this species as appeared contents. Occasionally, they may feed at from the density of plankton in the water bottom, in which case their guts were almost samples (Table 1). Presence of occasional filled with silt and sand/ unrecognizable empty stomach may be due to regurgitation detritus. The presence of unrecognizable or digestion of food items in fish stomachs as detritus or “marine snow” in the diet of S. the fish struggled for escape from the nets. aurita has been noted for this species in The vacuity index (VI) was high in summer other areas (Nieland, 1982) and for other which has been reported as spawning season related species such as the Indian oil sardine for S. aurita in the southeastern S. longiceps (Kumar and Balasubrahmanyan, Mediterranean (Pawson and Giama, 1985; 1989). The importance of “marine snow”, Wassef et al., 1985). This may be explained with its organic content and associated by the fact that during spawning, the fish had microorganisms, has been noted in the diet fully occupied abdominal cavity with the of many pelagic species (Gaughan and ripe gonads and empty stomach. The Mitchell, 2000). synchronization of the period of poor feeding Apart from detritus, an annual average activity with spawning season has been of the diet composition shows the reported for other fish species (Joadder, zooplankton–phytoplankton ratio in the food 90 Fedekar F. Madkour Feeding ecology of the round sardinella, Sardinella aurita as 3: 2. Similar feeding habits have been species. Thus, diet composition varied with reported for round sardinella in northeastern size classes probably due to the energy Mediterranean (Stergiou and Karpouzi, requirements, which vary according to the 2002). They classified it, according to their developmental stages. For fish >11cm in TROPH, as an omnivorous, filter feeder length, copepods were the main and most species with preference to animal prey, preferred prey that increased in importance whereas it was classified as an omnivore as the fish grow in size. The diet comprised with preference to plant material in other entirely these prey in the largest group of the areas (Nieland, 1982). A wide variety of specimens examined (15–16cm TL). The planktonic organisms were consumed by S. preference of larger sizes of S. aurita for aurita but copepods and diatoms were their copepods may be due to its ability to select main dietary component, making about three larger prey. Kahilainen (2004) mentioned quarter of the food; whereas all other items that particulate-feeding planktivores are size- contribute collectively only one-fourth selective predators and can visually detect, (Figure 3). The present result reveals that S. locate, and attack a single zooplankton aurita has a preference for copepods that individual. During ontogeny, fish often were most numerous in the diet during all change their diet, being able to exploit seasons except in autumn. This could be sequentially a series of prey sizes, ranging attributed to its ability to select its prey based from phytoplankton and small zooplankton on its large size, regardless of the abundance to much larger prey (Wootton, 1990). of smaller alternatives. For instance, high diatom densities in water samples collected 5. REFERENCES in winter (120249 individual/l) did not Abdel Aziz, N. and Gharib, S. 2007. Food correlate with a corresponding higher and feeding habits of round sardinella number for this abundant item in the diet of (Sardinella aurita) in El Mex Bay, S. aurita. Instead, copepods predominated in Egypt. Egyptian Journal of Aquatic the stomach contents even though they were Research, 33 (2): 202-221. found in lower numbers in the environment. Costal, J.L.; Almeida, P.R.; Moreira F.M. Furthermore, the highest consumption of and Costal, M.L. 1992. 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