Feeding habits of yellowfin seabream, Acanthopagrus latus in the northern region of the Persian Gulf

Feeding habits of yellowfin seabream, Acanthopagrus latus in the northern region of the Persian Gulf

I. Sourinejad1*, S. Nikkhah Khaje Ataei1, E. Kamrani1, M. Ghodrati Shojaei2

1-Dept. of Fisheries, Faculty of Marine and Atmospheric Sciences and Technologies, University of Hormozgan, Bandar

Abbas, Iran

2-Dept. of Marine Biology, Faculty of Marine Sciences, University of Tarbiat Modares, Noor, Iran

* Corresponding author’s E-mail: sourinejad@hormozgan.ac.ir

ABSTRACT

(Received: Feb. 08.2014  Accepted: jun. 07.2014)

Feeding habits of yellowfin seabream, Acanthopagrus latus was investigated in coastal waters of the Northern Persian Gulf. This investigation was conducted by monthly sampling of thirty fish from September 2011 through August 2012. Fish size ranged from 17.98 ± 2.07 to 32.31 ± 6.52 cm in total length and from 134.01 ± 45.62 to

720.46 ± 292.58 g in weight. The highest value of gastro-somatic index was obtained in September (5.22 ± 0.04)

and the lowest in December (1.61 ± 0.03) with annual average of 2.50 ± 0.60. The result of gastro-somatic index revealed that the highest feeding activity of A. latus was during autumn. The highest level of vacuity index was observed in summer (34.95 ± 4.71) and the lowest in autumn (25.88 ± 2.71) indicating that the highest number of

empty stomachs was in summer. Annual average of vacuity index was 30.14 ± 5.72 exhibiting that A. latus was comparatively gluttonous in the Northern Persian Gulf. Bivalves and shrimps were the major food items found in the stomach of A. latus showing food preference indices of 45.86% and 30.67%, respectively. Other food items included crabs (12.66%), aquatic plants (4.05%), animal derivatives (4.52%) and gastropods (2.23%). According to the results, animal derivatives, aquatic plants and gastropods were eaten accidentally and were not the food items of A. latus in coastal waters of Hormozgan. The average relative length of gut was 1.41 ± 0.15 showing that A. latus was omnivorous in this region.

 Keywords: Acanthopagrus latus, Feeding habits, Gastro-somatic index, Persian Gulf                                                           

INTRODUCTION

The quality and quantity of food directly af- fect fish growth while indirectly affect its mat- uration and mortality (Wootton, 1990). Stud- ies on feeding habits give information on the quality and quantity of food consumed by fish. Observations on fish prey preferences and feeding habits are mainly based on anal- yses of stomach contents. Stomach contents analysis can yield incidental but immediately valuable information since predators are of- ten better sampling devices than most com- mercial fishing gears. Feeding habits studies of fish are helpful in identifying some of the higher-level trophic relations in an ecosystem and are required for estimating fish produc- tion (Pauly & Christensen, 2000). In addition, knowledge of the feeding behavior of marine fishes is essential for fish stock assessment,

ecosystem modeling and to assess the role of marine fishes within ecosystem (Salavatian et al., 2011). Diet composition data also play a key role for the research on resource parti- tioning and within and between-species com- petition (Harmelin-Vivien et al., 1989), prey selection (Stergiou and Fourtouni, 1991), predator-prey size relationships (Scharf et al.,

2000), distribution of feeding habits with lati-

tude (Pauly, 2000) and habitat selection (Labropoulou et al., 1999). Yellowfin sea- bream (Acanthopagrus latus) is a commercially and ecologically important species that is widely distributed throughout the Indo-West Pacific region (Xia  et al., 2008). Like many other sparids, this fish is a protandrous her- maphrodite and usually inhabits relatively a wide  biogeographic  range  but  is  specially

Online version is available on http://research.guilan.ac.ir/cjes

found in warm shallow and coastal waters, often entering river mouths and estuaries (Li

& Ou, 2000; Xia et al., 2008). Various studies have been carried out about feeding habits of fish species. However, there is no considera- ble published information regarding feeding habits of marine fishes from the Northern Per- sian Gulf. Among the Persian Gulf fishes in Iranian waters, investigation of feeding habit of Platycephalus indicus (Hashemi and Taghavi Motlagh, 2013), Saurida tumbil (Vahabnezhad et al., 2013), Chirocentrus nudus (Khodadadi et al., 2012), Argyrosomus hololepidotus (Shekari & Hashemi, 2012), Sillago sihama (Taghavi Mot- lagh et al., 2012), sawtooth barracuda, Sphy- raena  putnamae  (Mohammadizadeh  et  al.,

2010) and Epinephelus coioides (Mohammadi et al., 2007) are the most recent ones. The present study  was,  therefore,  carried  out  to  gain

knowledge of the feeding habits and natural diet composition of yellowfin seabream (A. la- tus) in the Iranian waters of the Persian Gulf at Hormozgan Province. In terms of manage- ment, such studies are essential for evaluating the ecological role of the yellowfin seabream as well as understanding its position in the Persian Gulf food chains. The results also aimed at understanding the biology of preda- tor and prey species as well as their useful- ness for stock analyses. The findings can also be applied in aquaculture development.

MATERIALS AND METHODS Sampling and biometry

Fish specimens were collected monthly from

September 2011 through August 2012. Thirty fish per month were randomly sampled from Bandar Abbas landing sites in northern part of the Persian Gulf (Fig. 1).

Fig 1. Location of sample collection of A. latus in the Persian Gulf.

Totally, 360 fish were sampled and then as- sessed biometrically. The total length and the fork length of the sampled fish were meas- ured to the nearest 0.1 cm and the total weights to the nearest 0.1 g.

Gastro-Somatic Index (GaSI)

The specimens were properly cleaned in the

laboratory, dissected and the stomachs were removed. The total weight of the stomach with its contents was measured to the nearest

0.01 g. GaSi, based on monthly and seasonal

calculation  was  obtained  as  described  by

Biswas (1993):

GaSI=    (Total    weight   of    stomach/Body

weight) × 100.

Vacuity Index (VI)

Vacuity Index or the stomach emptiness in- dex determines the amount of the fish appe- tite for food and was calculated using the fol- lowing equation (Euzen, 1987):

VI= (The number of empty stomachs/total number of the stomachs examined) × 100.

The interpretation of the obtained VI is deter- mined  under  the  following  conditions (Euzen, 1987). If, 0≤VI<20, the logical conclu- sion is that the fish is gluttonous, 20≤VI<40, the    fish    is    comparatively    gluttonous,

40≤VI<60,    fish    is    middle    alimentary,

60≤VI<80, fish is comparatively hypoalimen-

tative, 80≤VI<100, fish is hypoalimentative.

Food Preference index (FP)

After dissecting the  stomachs, all the food

items in them were identified. To analyze the composition of the stomach and determine the food preference index, percentage fre- quency of occurrence was obtained through the following equation described by Chrisfi et al., 2007:

FP= (number of stomachs with a specific food

item/the number of non empty stomachs) ×

100.

The different values of this index, allow sepa- ration of the prey items into three categories: If FP >50%, the prey eaten is dominant and the main diet. If 50%> FP >10%, the prey

eaten is secondary and occur mainly if there is a lack of dominant prey. If F<10%, the prey is eaten accidentally and not the food of pred- ator at all (Euzen, 1987).

Relative Length of Gut (RLG)

Relative length of gut was measured to the

nearest 0.1 cm as described by Euzen (1987)

through the following equation:

RLG= Length of gut/total body length

If the amount of RLG is less than 1, the fish is

carnivorous and if it is more than 1, the spe- cies tends to be herbivorous and the medium values indicate that they are omnivorous spe- cies.

RESULTS

In this study, 360 specimens of A. latus were examined. According to the results, fish size ranged from 17.98 ± 2.07 cm (in September) to

32.31 ± 6.52 cm (in January) in total length and from 134.01 ± 45.62 g (in September) to 720.46

± 292.58 g (in January) in weight (Table 1).

Table 1. Biometric results of A. latus specimens in the Persian Gulf from September 2011 through August 2012 (Mean ± SD) (N = 360).

Month

Total length (cm)

Total weight (g)

Month

Total length (cm)

Total weight (g)

September

17.98 ± 2.07

134.01 ± 45.62

March

31.00 ± 2.90

603.13 ± 138.53

October

25.94 ± 4.85

361.94 ± 157.76

April

27.49 ± 5.18

407.54 ± 221.15

November

22.21 ± 6.17

263.67 ± 200.23

May

25.14 ± 3.59

304.49 ± 118.85

December

30.40 ± 4.72

608.25 ± 270.02

June

26.26 ± 5.69

398.81 ± 250.68

January

32.31 ± 6.52

720.46 ± 292.58

July

26.45 ± 2.17

377.63 ± 75.35

February

30.23 ± 3.32

510.54 ± 169.55

August

21.08 ± 2.06

232.23 ± 65.32

34                                                                                                                                                       Feeding habits of….

Table 2. The average GaSI in examined A. latus from September 2011 through August 2012 (N = 360).

Table 3. The average vacuity index in examined A. latus from September 2011 through August 2012 (N = 360).

Table 4. The average FP index in examined A. latus from September 2011 through August 2012 (N = 360).

GaSI values are presented in Table 2. This in- dex  had  the  highest  value  in  September (5.22 ± 0.04) and the lowest in December (1.61

±  0.03).  The  maximum value  of  GaSI  was

found in autumn and its minimum in sum- mer. The annual average of GaSI was 2.50 ±

0.60. Table 3 contains the results of VI. The an- nual average of this index was 30.14 ± 5.72. The highest level of VI was observed in Au- gust (39.39) and summer (34.95 ± 4.71). The lowest level of VI was found in autumn (25.88

± 2.71).

According to the results of food preference in-

dex, bivalves and shrimps were the  major food items found in the stomach of A. latus. The FP index (%) was 45.86 for bivalves and

30.67 for shrimps in the whole period. Other

food items included crabs (12.66%), aquatic plants  (4.05%),  animal  derivatives  (4.52%) and gastropods (2.23%).

Seasonal occurrence of different food items in the stomach of A. latus is shown in Table 4. High percentage occurrence of bivalves was recorded during all seasons i.e. autumn, win- ter,  spring  and  summer  (48.48%,  37.70%,

49.05% and 48.21%, respectively). Animal de-

rivatives (eggs, scales, insect and crustaceans appendages, etc.) in the stomach in autumn and winter constituted 8.99% and 9.10%, of the food items respectively. Aquatic plants also constituted 9.75% and 6.45% of the food items in winter and spring, respectively.

The average relative length of gut was 1.41 ±

0.15 indicating that A. latus exhibits omniv- orous feeding behavior in coastal waters of Hormozgan in the Persian Gulf.

DISCUSSION

According to the results, the maximum value of gastrosomatic index was found in autumn and the minimum in summer. Gastrosomatic index in autumn was higher than the annual average while was lower than the annual av- erage in summer. Calculation of gastro-so- matic index is a useful and efficient way of comparing the status of food consumption. The present results showed that the heaviest stomachs and subsequently, the highest feed- ing activity of A. latus  occur in autumn. The results also showed that the feeding activity is reduced during the summer.

Vacuity index estimates the veracity of the predator fish. The higher the voracity of fish species, the lower the percentage of empty

stomachs. The annual average of vacuity in- dex was found to be 30.14 ± 5.72. Since this value is between 20 and 40, So A. latus is clas- sified as comparatively gluttonous in coastal waters  of  Hormozgan, North  Persian  Gulf (Euzen, 1987).

The highest level of vacuity index and also, the maximum numbers of empty stomachs were observed in summer, while the mini- mum in autumn. Changes in the number of empty and full stomachs during the year in- dicate differences in feeding intensity. Feed- ing intensity is negatively related to the per- centage of empty stomachs (Shalloof & Kha- lifa, 2009). In the present study, the highest feeding intensity and also the lowest percent- age of empty stomachs were found in au- tumn. However, the results of GaSI and VI both indicate that the highest feeding activity of A. latus occur in autumn. Cabral and Murta (2002) and Santic et al. (2005) have stated that feeding intensity through the analysis of empty stomachs is well correlated with sea- sons.

Feeding intensity in fish is synchronized with their spawning seasons (Dadzie et al., 2000; Salavatian et al., 2011). Most aquatic animals generally do not feed during the reproductive season, or their feeding habits are greatly de- creased. The fact indicates that there is a close relationship between the reproductive season and feeding activity. Available reports sug- gest that the higher occurrence of empty stomachs during the spawning season of fishes is due to the decreased feeding activity since the mature gonads take up more space in the peritoneal cavity, compressing the stomach and making feeding more difficult (Dadzie et al., 2000).

This study also revealed that feeding activity

is at its peak before the spawning season. Fur- thermore, the stomachs were found to be less empty in autumn which could be related to the increased feeding activity to meet the de- mand for more energy in spawning season. This fact notes that the feeding habit in A. la- tus has a close relation with its reproduction. Spawning of A. latus in the Persian Gulf takes place from January through March with spawning peak in March (Nikkhah Khaje Ataei et al., 2013). Gonadosomatic index in this species begins to increase gradually from September through February and then reaches strikingly to its peak in March. It can

be concluded that the feeding activity in- creases during the early stages of maturity to provide the energy for final maturation and spawning. Hence, feeding decreases in spawning season. This result is in line with those of some other marine species including Pampus argenteus and Sillago sihama (Dadzie et al., 2000; Shalloof & Khalifa, 2009).

In silver pomfret (Pampus argenteus), feeding

was intensive during the early stages of ma- turity and decreased as the gonads mature (Dadzie et al., 2000). In Indian waters, Pati (1980) stated that in mature fish of silver pom- fret, the space inside the body cavity was re- duced because of the growth of the reproduc- tive  organs pushing the  digestive tract  to- ward the dorsal side. On Sillago sihama, the abdominal cavity was fully occupied by the ripe  gonads in  summer and  led  to  empty stomachs (Shalloof & Khalifa, 2009; Taghavi Motlagh et al., 2012).

Feeding intensity decreases during the win- ter months when the temperature drops. This assumption broadly agrees with the ther- mophilous fish growth model from seas of medium geographic latitudes with lowest growth rate in winter and higher spawning rates in summer. This is due either to a tem- perature-dependent physiological process (Santic et al., 2005), a strong temperature-de- pendent regulation of food intake (Temming and Hermann, 2001), or lesser abundance of prey and the lowered metabolism, which probably reduce predation during the winter (Santic et al., 2005). In contrast, the monthly variations in GaSI and VI revealed a low feed- ing intensity during high temperature season (summer) and a higher feeding intensity dur- ing the period of low temperature (in autumn and winter). These findings strengthen the evidence that in the Persian Gulf, feeding in- tensity in A. latus is likely related to the repro- ductive cycle rather than the seasonal climatic changes.

Based on the results of VI, some of the stom-

achs were empty. Euzen (1987) reported sim- ilar observations in Epinephelus tauvina in Ku- waiti waters. Mohammadi et al. (2007) also made similar observation in Epinephelus coi- oides  in  the  Persian  Gulf.  Empty stomachs maybe either related to regurgitation of prey during coming to surface or rapid digestion of food that takes place in the tropical waters as the metabolic rate is high (Kalita & Jayaba- lan, 2000).

Considering the results of FP, the annual av- erage of food preference index (%) was ob- tained 45.86 for bivalves, 30.67 for shrimps and 12.66 for crabs. According to Euzen (1987), since these values of FP are between 10 and 50, bivalves, shrimps and crabs are the secondary food items of A. latus in coastal wa- ters of Hormozgan. However, in comparison to other preys, bivalves and shrimps were the major food items found in the stomach. Ani- mal derivatives, aquatic plants and gastro- pods also occurred with FP indices of lower than 10, revealing that these items are eaten accidentally and not the food items of this predator.

Nasir  (2000)  reported that  bivalves, crabs,

shrimps, amphipods, aquatic plants and aquatic insects were the  food items in  the stomach of A. latus in Khor Al-Zubair in the Northwestern Persian Gulf. The diet of most fishes will change based on a number of fac- tors, either intrinsic (e.g. size, behavior, taxon- omy) or extrinsic (e.g. biotope, region) (Pauly et al., 1998). However, the food preference of predatory fishes is very complex and is influ- enced by many factors. The age of fish, prey accessibility and mobility, prey abundance, prey energy content, prey size selection and seasonal changes are among these factors (Stergiou & Fourtouni, 1991). It seems that the mollusks and crustaceans are available enough to A. latus in Hormozgan waters to constitute the most important preys of this species.

Based on the seasonal analysis of stomach contents, benthic organisms including bi- valves, shrimps and crabs composed the ma- jor food items in all seasons. Some small dif- ferences were observed in stomach contents in different seasons. Animal derivatives were only found in autumn and winter, aquatic plants in winter and spring and also gastro- pods in summer.   Noteworthy, the effect of seasonality should always be considered in the studies on feeding of fish, because the temporal changes of biotic and abiotic factors alter the structure of the food chain along the year; consequently, fish often shows seasonal diet shifts (Shalloof & Khalifa, 2009). Seasonal fluctuations in diet composition of fishes else- where have been attributed to the influence of the monsoons, when peak occurrences of cer- tain food organisms are observed (Pati, 1980) and seasonal fluctuations in water tempera- ture when food organisms peak in summer