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Research Article
Food and feeding habits of Indian halibut, Psettodes erumei from the North of the Persian Gulf and Oman Sea
Mehri GHANBARZADEH1, Ehsan KAMRANI*2, Mohammad Sharif RANJBAR1, Ali SALARPOURI3, Carl WALTERS4
1Department of Marine biology, Faculty of Marine Sciences and Technologies, University of Hormozgan, Bandar Abbas, Iran.
2Fisheries Department, Faculty of Marine Sciences and Technologies, University of Hormozgan, Bandar Abbas, Iran.
3Persian Gulf and Oman Sea Ecological Center, Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research Education and Extension Organization (AREEO), Bandar Abbas, Iran.
4Fisheries Centre, The University of British Columbia, 2204 Main Mall, Vancouver, BC V6T 1Z4, Canada.
*Email: eza47@yahoo.com
Abstract: Indian halibut, Psettodes erumei is the single member of family Psettodidae recorded in the southern waters of Iran (north of the Persian Gulf and Oman Sea). In the present study, the feeding habit of this species was investigated. The specimens were collected monthly from October 2016 to November 2017 by shrimp trawl from three sampling sites along the northern parts of the Persian Gulf and Oman Sea (Hormozgan Province, Iran). For the diet analysis, the stomach contents of 433 individuals were analyzed.
Of these, 277 were empty (VI=63.97%) which varied significantly throughout the study period. Feeding intensity of both sexes was high before the gonadal maturation peak; during the period when a maximum percentage of fully mature individuals were present, the feeding intensity was found to be low. The overall diet showed that Indian halibut is mainly a piscivorous carnivore and Teleostei were the most frequent and important food group in the diet (%F=48.08, %IRI=98.44). Crustacean and Cephalopods constituted a small portion of the diet (%F=5.77 and 1.92, respectively) and were of minor importance (%IRI=1.33 and 0.23, respectively). Diet composition showed no significant variation in relation to season, fish size and sex and only some significant differences were observed in their frequency and numerical percentage. The trophic level for this species was calculated 4.4. The present study provides partial information on feeding habits of Indian halibut, of prime importance for the fisheries management and also helps to understand the trophic role of fish in relation to other species in the ecosystem.
Keywords: Flatfish, Diet analysis, Seasonal variations, Sex.
Citation: Ghanbarzadeh, M.; Kamrani, E.; Ranjbar, M.S.; Salarpouri, A. & Walters, C. 2020.
Food and feeding habits of Indian halibut, Psettodes erumei from the North of the Persian Gulf and Oman Sea. Iranian Journal of Ichthyology 7(2): 167-180.
Introduction
Feeding is one of the main activities of everyday living in fishes which profoundly influences fish life stages especially growth, migration and distribution, spawning, healthy and survival (Priyadharsini et al.
2014). Generally, analysis of feeding dynamics in fishes allows understanding the diet, determining the trophic level and roles within the ecosystem.
Flatfishes are one of the economically and ecologically remarkable component of continental shelf, deep ocean, small marine areas and estuarine
ecosystems across the world (Link et al. 2005). In the north of the Persian Gulf and Oman Sea, the flatfishes support a fishery of commercial importance. The flatfish Psettodes erumei (Bloch and Schneider, 1801) commonly known as Indian halibut and belongs to the family Psettodidae, is the single member of this family that lives in the Persian Gulf and Oman Sea and also in the southern waters of Iran (Hensley 1997; Yasemi et al. 2008). Indian halibut has a wide distribution along the southern waters of Iran and is one of the by-catch species of commercial
bottom trawl fisheries in the area and in recent years, has been considered as a high-quality product in local fish markets.
Previous studies on this species looked at some biological aspects including age, growth, reproduction and feeding habits in both the east and west coast of India (Pradhan 1969; Abraham & Nair 1976; Darracott 1977; Das & Mishra 1990). In spite of the wide distribution and commercial importance of Indian halibut in the north of the Persian Gulf and Oman Sea, little is known about different aspects of its biology such as feeding habits and the only data on its dietary patterns in the area were reported by Azh et al. (2015). However, our knowledge about the trophic ecology of this species in the north of the Persian Gulf and Oman Sea is very little. Present study is the first comprehensive study on the food and feeding habits of Indian halibut in the northern parts of the Persian Gulf and Oman Sea (Hormozgan Province, Iran) in order to determine its dietary composition, feeding intensity and also differences in feeding habits in relation to season, fish size and sex.
Materials and Methods
Sampling and laboratory handling: Indian halibut specimens were collected monthly during the period between October 2016 and November 2017 by shrimp trawl from three sampling sites along the northern parts of the Persian Gulf and Oman Sea (Hormozgan Province, Iran) (Fig. 1). Immediately, total length (TL, ±0.1cm) and total weight (TW,
±0.1g) were measured for each specimen and specimens were slit along the abdomen and the stomachs were removed and fixed in 10% buffered formalin. Then, the specimens were stored in iceboxes and transferred to the Persian Gulf and Oman Sea Ecological Research Institute laboratory at Bandar Abbas for further analysis. In the laboratory, the sex of each specimen was recorded by macroscopic examination of the gonads. To investigate the food and feeding habits, the stomach of each specimen was analyzed. First, the stomachs were weighed to the nearest 0.1g; then each stomach
was emptied into a Petri dish and the empty stomach was also weighed. Stomach contents were examined under a dissecting microscope and the food items, when possible, identified to the lowest taxa level according to appropriate taxonomic identification guides (Fischer & Bianchi 1984; Randall 1995;
Assadi & Dehghani 1997; Carpenter et al. 1997). The stomach contents were weighed, and enumerated for each prey item when the state of digestion was not advanced. For digested matter only the weight was recorded.
Data analysis and feeding indices: Data analysis was done using some indices as follows:
(i) Vacuity index: (VI)=100×(number of empty stomachs/number of examined stomachs) (Berg 1979), it was observed that some empty stomachs were shrunk and contained mucus, while others were expanded but completely empty; as expressed by Daan (1973) the latter type happens in fish which have recently regurgitated.
(ii) The Gastrosomatic index (GaSI) for each month was calculated as: GaSI=100×(weight of stomach/weight of fish) (Desai 1970).
(iii) Frequency of occurrence: (%F)=100×(number of stomachs in which an especial food item was found/total number of stomach containing food), (iv) The numerical percentage of prey items:
(%N)=100×(number of each prey item in all full stomachs/total number of observed food items in all stomachs in a sample),
(v) The mean percent weight: (%W)=100×(weight of Fig.1. Location of the different region of Hormozgan,
* = sampling sites.
each prey item in all full stomachs/total weight of observed food items in all stomachs in a sample) (Hyslop 1980)
(vi) The index of relative importance: (IRI)=
(%N+%W) ×%F and %IRI = IRI
∑ IRI× 100 (Pinkas et al. 1971).
Schoener overlap index: For determination of diet similarity among seasons, months and length-classes, the Schoener Overlap Index (Cxy) was used according to the following equation (Schoener 1970):
𝐂𝒙𝒚= 1 − 0.5 ∑|𝑝𝑥𝑖− 𝑝𝑦𝑖|
Where pxi and pyi are the estimated proportions by the number of prey type i in the diets of groups (month or season, length) x and y, respectively. The value of this index is between 0 and 1 and if it is bigger than 0.60, the diet of the 2 groups is similar and usually considered to be "biologically significant" (Wallace 1981).
Relative length of gut: The length of gut was measured with the accuracy of 0.02 mm in order to obtain Relative Length of Gut (RLG) using the following equation: RLG=Length of the gut/Total fish length (Yamagishi et al. 2005).
Trophic level: For determination of trophic level the following equation was used (Christensen & Pauly 1992):
𝑇𝐿 = 1 + (∑ 𝑃𝑗 × 𝑇𝐿𝑗
𝑛
𝑖=1
)
Where TLj is the trophic level of each prey item j which was taken from Fishbase (Froese & Pauly 2000) and some other published accounts of the
organisms of the Persian Gulf and Oman Sea (Vahabnezhad et al. 2013; Rastgoo et al. 2014;
Vahabnezhad et al. 2015). Trophic level values for families and orders were taken from the mean of estimates for their dominant individual species in the area. According to the results of feeding habit, the prey items consumed by Indian halibut were grouped into various categories which their trophic levels have been shown in Table 1. Pj is the estimated proportion by the number of prey type j.
Statistical analysis: Statistical analyses were performed in Microsoft Excel 2016, SPSS (Version 22) and R (Version 3.3.3). To examine the normality of data the Kolmogorov-Smirnov test (P<0.05) was used. Statistical differences in GaSI values among different months and different size-classes were tested by nonparametric K independent samples test (Kruskal-Wallis-H) and for comparison between sexes, nonparametric 2 independent samples (Mann- Whitney-U) test was applied. Statistical differences of the frequency of occurrence index and also vacuity index with respect to month or season, size and sex were assessed by a chi-square test in R software. All statistical analyses were performed in 95% of confidence level.
Results
From a total of 433 specimens collected during the sampling period, 231 females and 177 males were sexed and 25 specimens were undetermined and could not be sexed. Total length and total weight of collected specimens ranged between 18.5 and 64cm Table 1. Trophic level of food items of Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea.
Prey items Trophic level Reference
Nemipterus japonicus 4.1 (Rastgoo et al. 2014)
Upeneus sulphureus 3.5 (Froese & Pauly 2000) (Fishbase) Muraenesox cinereus 4.4 (Froese & Pauly 2000) (Fishbase)
Saurida tumbil 4.6 (Vahabnezhad et al. 2013)
Nematolosa sp. 2.2 (Vahabnezhad et al. 2013)
Leiognathus sp. 2.6 (Vahabnezhad et al. 2015)
Carangidae 4.2 (Froese & Pauly 2000) (Fishbase)
Other teleost fishes (unid)† 3.5 (Froese & Pauly 2000) (Fishbase Sepia sp. 3.5 (Froese & Pauly 2000) (Fishbase) Crustacean (Crab and Shrimp) 2.5 (Froese & Pauly 2000) (Fishbase)
†Unidentified
(39.81±8.5) and between 96.4 and 4068g (1038.48±668.4), respectively.
Of the 433 stomachs examined, 277 were empty (VI=63.97±15.44%). VI was high round the study period and varied from 40 to 83.33%. This index significantly varied over the study period (X²=48.67, D.F.=13, P<0.05). The distribution of empty stomachs across season showed that the maximum and minimum of VI occurred during autumn 2016 and summer 2017, respectively (Fig. 2). The mean annual VI significantly differed among the size- classes (X²=27.14, D.F.=8, P<0.05) with a maximum
value in >60cm size-class and a minimum in 25.1- 30cm size-class (Table 2). In addition, VI computed by sex presented significant monthly variations for both females (VI=59.4%; X²=63.24, D.F.=13, P<0.05) and males (VI=72.98%; X²=53.44, D.F.=13, P<0.05). Comparison of monthly VI values between sexes showed significant differences (P<0.05) and they were lower in females over the study period.
According to GaSI values, the feeding intensity in females was higher in February- March and August- September; but this difference was not statistically significant with other months (D.F.=13, P>0.05). In Table 2. Variations of the vacuity index (VI, %) of
Indian halibut Psettodes erumei in different size- classes in the north of the Persian Gulf and Oman Sea.
Size-classes VI (%)
≤25 56.25
25.1-30 50.00
30.1-35 72.88
35.1-40 68.57
40.1-45 65.96
45.1-50 59.74
50.1-55 54.17
55.1-60 60.00
>60 95.00
Fig.2. Seasonal variation (± standard deviation) in percentage of empty stomachs for Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea.
Fig.3. Mean monthly variations in gastrosomatic index of females and males of Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea. The error bars correspond to the standard deviation.
males, significant difference was observed throughout the study period (D.F.=13, P<0.05) and the feeding intensity was higher from February to April and from July to September (Fig. 3). GaSI showed significant differences between the two sexes throughout the study period and its values were higher in females than that of males (P<0.05). The mean annual GaSI values did not show any significant variation among the size-classes (D.F.=8, P>0.05). The maximum and minimum values were observed in 50.1-55 and >60 size-classes, respectively (Table 3).
The stomach contents of Indian halibut consisted
of eleven different taxa belonging to three major food categories (Table 4). According to Table 4, the overall diet was mainly composed of Teleostei, but Crustacean and Cephalopods were also found in the stomach contents. Seven different types of Teleostei were identified in the stomach contents. The %IRI showed that among Teleostei, Leiognathus sp., Nemipterus japonicas, and Saurida tumbil were the most important prey items and constituted the highest frequency and numerical percentage. It is interpretable from the values of mean percentage weight that digested matter was highly accumulated in the stomachs of Indian halibut.
Table 3. Variations of the gastrosomatic index (± standard deviation) of Indian halibut Psettodes erumei in different size-classes in the north of the Persian Gulf and Oman Sea.
Size-classes GaSI
≤25 0.84±1.45
25.1-30 0.60±1.02
30.1-35 0.41±1.12
35.1-40 0.58±1.79
40.1-45 0.47±1.44
45.1-50 0.48±1.71
50.1-55 1.21±2.62
55.1-60 0.71±1.74
>60 0.21±0.31
Table 4. Prey items identified in the stomach contents of Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea. (%F = frequency of occurrence; %N = percentage of numerical abundance; %W = mean percent weight;
%IRI = percent of relative importance index).
Major food groups and species % F % N % W %IRI
Teleostei
Nemipterus japonicus 2.56 3.50 2.69 0.44
Upeneus sulphureus 1.28 1.59 0.71 0.08
Muraenesox cinereus 0.64 1.19 0.65 0.03
Saurida tumbil 2.56 5.36 1.88 0.52
Nematalosa sp. 0.64 1.43 1.43 0.05
Leiognathus sp. 4.49 7.86 3.57 1.42
Carangidae 0.64 2.38 0.75 0.05
Fish (unid)† 35.26 63.41 33.98 95.63
Total teleostei 48.08 86.71 45.71 98.44
Crustacea (Decapoda)
Crab (unid) † 3.85 4.01 3.13 0.77
Shrimp (unid) † 2.56 4.70 3.27 0.57
Total Decapoda 5.77 8.70 6.18 1.33
Cephalopoda
Sepia sp. 1.92 4.59 3.33 0.42
Total Cephalopoda 1.92 4.59 3.33 0.23
Digested matter − − 44.78 −
†Unidentified
Seasonal variations in the major food groups showed that Teleostei and Crustacean were observed in the diet in all seasons and had the highest frequency in winter, while Cephalopods were only observed in autumn. The highest number of Teleostei and Crustacean were observed in spring and winter,
respectively (Table 5). The mean percent weight calculated for Indian halibut determined that most of the food was digested during summer (Fig. 4).
Diet composition for size-classes of the three major food groups is shown in Table 6. Feeding habit showed no obvious change with the increase of the Table 5. Seasonal variation in frequency of occurrence (%F), numerical percentage (%N) and percent of relative importance index (%IRI) of major food groups of Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea.
Teleostei Crustacea Cephalopoda
Season n %F % N % IRI %F % N % IRI %F % N % IRI
Autumn 2016 24 50 75.93 25.37 10.71 7.41 2.28 8.33 16.67 5.69
Winter 2017 28 60.71 80.71 31.06 16.67 19.30 2.27 0 0 0
Spring 2017 36 44.44 94.44 32.81 2.78 5.56 0.52 0 0 0
Summer 2017 44 47.73 91.67 33.04 2.27 8.33 0.30 0 0 0
Autumn 2017 24 37.50 92.86 49.27 0 0 0 4.17 7.14 0.73
n: number of individuals
Table 6. Variations in frequency of occurrence (%F), numerical percentage (%N) and percent of relative importance index (%IRI) of major food groups with respect to size for Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea.
Teleostei Crustacea Cephalopoda
Size-classes n % F % N %IRI % F % N %IRI % F % N %IRI
25≥ 14 71.43 91.67 97.10 14.29 8.33 2.89 0 0 0
25.1-30 13 53.85 83.33 96.88 7.69 16.67 3.11 0 0 0
30.1-35 16 50 100 98.94 5.11 6.2 1.05 0 0 0
35.1-40 33 36.36 78.33 94.52 6.06 11.67 3.02 6.06 10 2.45
40.1-45 32 50 88.89 97.93 6.25 11.11 2.06 0 0 0
45.1-50 31 32.26 79.63 94.38 6.45 14.81 4.50 3.23 5.56 1.10
50.1-55 11 63.64 100 100 0 0 0 0 0 0
55.1-60 6 83.33 100 100 0 0 0 0 0 0
n: number of individuals
Fig.4. Seasonal variation of mean percent weight (%W) of different Food groups of Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea.
body length. Teleostei were the most important prey group in all size-classes. Numerical percentage of this group was higher than 75% in all size-classes.
Crustacean were present in all size-classes except for those larger than 50cm and the highest frequency and mean number of this group were recorded in smaller individuals. Cephalopods were comparatively low
and of less importance and were only present in 35.1- 40.0 and 45.1-50cm size-classes and their mean number was higher in 35.1-40cm size-class. For these major food groups, statistical analysis revealed significant variations in frequency of occurrence among different size-classes (P<0.05). The index of relative importance indicated that smaller individuals Table 7. Estimated dietary overlap (Schoener's index) for Indian halibut Psettodes erumei according to months in the north of the Persian Gulf and Oman Sea.
Nov-16 Dec-16 Jan-17 Feb-17 Mar-17 Apr-17 May-17 Jun-17 Jul-17 Aug-17 Sep-17 Oct-17 Nov-17
Oct-16 0.50* 0.50* 0.80 0.67 0.95 0.83 1.00 1.00 0.75 1.00 1.00 0.86 1.00
Nov-16 0.50* 0.98 0.89 0.82 0.94 0.78 0.78 0.97 0.78 0.78 0.78 0.78
Dec-16 0.50* 0.50* 0.50* 0.50* 0.50* 0.50* 0.50* 0.50* 0.50* 0.64 0.50*
Jan-17 0.87 0.85 0.97 0.80 0.80 0.95 0.80 0.80 0.80 0.80
Feb-17 0.71 0.83 0.67 0.67 0.92 0.67 0.67 0.67 0.67
Mar-17 0.88 0.95 0.95 0.80 0.95 0.95 0.86 0.95
Apr-17 0.83 0.83 0.92 0.83 0.83 0.83 0.83
May-17 1.00 0.75 1.00 1.00 0.86 1.00
Jun-17 0.75 1.00 1.00 0.86 1.00
Jul-17 0.75 0.75 0.75 0.75
Aug-17 1.00 0.86 1.00
Sep-17 0.86 1.00
Oct-17 0.86
*No Significant Schoener Overlap
Table 8. Estimated dietary overlap (Schoener's index) for Indian halibut Psettodes erumei according to seasons in the north of the Persian Gulf and Oman Sea.
Seasons Winter 2017 Spring 2017 Summer 2017 Autumn 2017
Autumn 2016 0.83 0.81 0.83 0.83
Winter 2017 0.86 0.89 0.81
Spring 2017 0.97 0.93
Summer 2017 0.92
Fig.5. Mean percent weight (%W) of different Food groups according to different size-classes for Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea.
of Indian halibut seek Teleostei and Crustacean and as they grow became more piscivorous. The highest rate of digestion was found in the middle group size individuals (individuals of 35 to 45cm TL) (Fig. 5).
Considering the feeding habits by sexes, female and male diets were approximately similar and all major food groups were present in both sexes.
Teleostei was the most important food group in both sexes (%F in females and males: 47.96 and 42.55;
%N in females and males: 92.56 and 80, %IRI in females and males: 99.39 and 96.49, respectively).
Statistical analysis showed a significant difference in frequency of three major food groups in both females (X²=158.53; D.F.=13, P<0.05) and males (X²=399.36, D.F.=13, P<0.05) throughout the study period. The mean percent weight of prey items revealed that digested matter was the chief material found in the stomachs in both sexes of Indian halibut
(Fig. 6).
Feeding strategy of Indian halibut in December was different with other months (except October) as the C value was smaller than 0.60 (Table 7). The feeding strategy in all seasons was similar (Table 8);
also diet composition was similar among all size- classes (Table 9). Length of Gut ranged between 0.96 and 4.06cm. The mean Relative Length of Gut (RLG±S.D.) was measured as 0.043±0.01. The trophic level of Indian halibut in this study was found to be 4.4.
Discussion
Feeding intensity (GaSI) is negatively related to the percentage of empty stomachs (Vacuity Index) (Bowman & Bowman 1980). The vacuity index of all individuals together was estimated 63.97% during the study period and since this value is more than 60 Table 9. Estimated dietary overlap (Schoener's index) for Indian halibut Psettodes erumei according to size-classes in the north of the Persian Gulf and Oman Sea.
Size- classes 25.1-30 30.1-35 35.1-40 40.1-45 45.1-50 50.1-55 55.1-60
≤25 0.92 0.92 0.87 0.97 0.88 0.92 0.92
25.1-30 0.83 0.90 0.94 0.94 0.83 0.83
30.1-35 0.78 0.89 0.80 1.00 1.00
35.1-40 0.89 0.96 0.78 0.78
40.1-45 0.91 0.89 0.89
45.1-50 0.80 0.80
50.1-55 1.00
Fig.6. Variations in mean percent weight (%W) of different food groups with respect to sex for Indian halibut Psettodes erumei in the north of the Persian Gulf and Oman Sea.
and less than 80 (60≤VI=63.97%< 80), so, according to the classification of Euzen (1987) for VI values, this species is relatively abstemious feeder. The high VI value observed in this study may be due to the fishing gear and/or to the feeding behavior of fish at the moment of capture (Verheijen & De Groot 1979).
Also, it could be stated that the capture of individuals may have occurred before the ingestion of prey items and/or after digestion process, so, many individuals would have had an empty stomach at the moment that they have been collected (Shafahipour 2005). VI showed significant variations during the study period; in both sexes, the lowest VI and the highest GaSI values were recorded before the gonadal maturation peak (Ghanbarzadeh et al. unpublished data). VI values in females were lower than males during the study period and also females had a higher feeding intensity than males, as they need to consume more energy for the maturation of their gonads (Fehri-Bedoui et al. 2009). The high VI values revealed low feeding intensity in both sexes during the gonadal maturation peak, when a maximum percentage of fully mature individuals were present and did not have any active feeding. After gonadal maturation peak, feeding intensity was relatively high to compensate the loss of energy due to reproductive activity (Ghanbarzadeh et al.
unpublished data).
According to these results, there is a close relationship between feeding intensity and reproduction period of Indian halibut and efforts to gain energy for the development of gonads and reproduction have led to an increase in its feeding intensity before gonadal maturation peak. In most fish species, it has been proved that the feeding intensity reduces during the reproductive activity when the specimens bear developed gonads (Pati 1980; Menon 1984). Ramanathan & Natarajan (1979), Das & Mishra (1990) and Azh et al. (2015) reported similar trends for VI and GaSI of the same species. Similar to Indian halibut, some differences in the patterns of the vacuity index and feeding intensity were reported for other resident fish of the
Persian Gulf and Oman Sea, such as S. tumbil (Vahabnezhad et al. 2013) and Cynoglossus arel (Rajaguru 1993). In general, the high vacuity index and low feeding intensity observed during the study period could also be due to the other factors such as lower availability and abundance of prey items or less exposure to predation in most periods (Harmelin- Vivien et al. 1989; Pallaoro et al. 2003), light intensity changes and tidal conditions (Thijssen et al.
1974).
The present study showed that Teleostei were the most common and important prey group in the diet of Indian halibut. Other prey groups (Crustacean and Cephalopods) were of minor importance. This finding is in accordance with the results of Devadoss et al. (1977) and Azh et al. (2015). Das & Mishra (1990) also reported the presence of the same prey groups and an additional prey group, ″Echinoderms″
which formed a minor component of the diet of Indian halibut. Three aforesaid studies also showed that Teleostei constituted the main food group. The most important consumed Teleostei were Leiognathus sp., N. japonicas and S. tumbil which is similar to those reported by Devadoss et al. (1977).
The presence of Teleostei as the main prey group conforms to those of some other flatfish species reported by several authors (Martin & Sandercock 1967; Castillo-Rivera et al. 2000). In general, results of this study and previous studies imply that Indian halibut is highly predacious and mainly a piscivorous species.
Seasonal investigation of major food groups showed that Teleostei and Crustacean were present in the diet in all seasons and had the highest frequency in winter while Cephalopods were only observed in autumn. The highest number of Teleostei and Crustacean were observed in spring and winter, respectively. It reveals that however Indian halibut somehow takes advantage of some seasonally abundant prey items in the study area, but the change of season does not seem to have any significant effect on its diet composition and this variability in frequency and numerical percentage of prey groups
is probably related to variations in availability, abundance and vulnerability of these prey groups in the environment, rather than variations in nutritional recruitments of Indian halibut throughout the study period. Seasonal variations in the frequency and numerical percentage of prey groups in the diet of some other flatfishes have already been reported (Livingston 1987; Molinero & Flos 1991; Garcia- Franquesa et al. 1996; Castillo-Rivera et al. 2000) which could be related to the changes in the life- history patterns of prey groups (Worobec 1984;
MacDonald & Green 1986), changes in the feeding activities of predator (Wootton 1990) and available habitat for foraging, its abiotic factors and condition.
As the results of this study, finding of Das & Mishra (1990) on the feeding habits of the same species showed no clear seasonal changes.
According to the data obtained, Teleostei were consumed by all size-classes, but were more pronounced in larger size-classes. Crustacean were present in all size-classes except for those larger than 50cm and Cephalopods were only consumed by some certain size-classes. The index of relative importance showed that smaller individuals seek Teleostei and Crustacean and as they grow became more piscivorous. Ontogenetic changes in the feeding habits of a given species are a kind of adaptation to use available food, avoid intra and interspecific competition, and enable the catching of larger and more energetic preys (Amara et al. 2001; Amezcua et al. 2003). All flatfish species eat small benthic crustaceans at some periods in their life history.
Many of the piscivores flatfishes may consume polychaetes and meiofauna when they are of smaller sizes, but grow out of this feeding mode (Aarnio et al. 1996; Garrison & Link 2000). De Groot (1969, 1971) reported that fishes of the family Psettodidae are very predacious in their habit and they feed exclusively on fish. The data of Das & Mishra (1990), on the feeding habits of different size-classes of Indian halibut, agree with ours. In their report, no clear change was observed in the feeding habit with the increase of the body length. Also, observations of
Devadoss & Pillai (1973) and Devadoss et al. (1977) on the feeding habit of the same species showed the piscivorous nature of both the juveniles and adults.
The accumulation of digested matter in the fish diet was higher in fishes of middle size. This shows that these groups required less energy to capture the prey and to utilize their energy mostly in the development of gonads (Farooq et al. 2017). On the other hand, larger individuals exploited more energy in searching for food.
Although in some flatfish species feeding habit was different between sexes (Molinero & Flos 1991), the feeding habit of Indian halibut in the present study was not different between females and males and all major food groups were present in both sexes and there was a diet overlap between females and males. As a result, gender appeared not to have had any significant effect on the diet composition.
Similar findings have been reported on some other flatfish species (Garcia-Franquesa et al. 1996;
Castillo-Rivera et al. 2000). This may suggest the presence of more or less similar niches and a compatibility between sexes in spatial or seasonal habitat overlap (Contente & Stefanoni 2010). In fact, it seems that there is no spatial or seasonal habitat segregation between females and males of Indian halibut.
Values of Schoener overlap index were obtained from a comparison among different months, seasons and size-classes. Most of the values were >0.60.
Accordingly, a high dietary overlap was observed throughout all size-classes, seasons and most of the months and only a decrease in dietary overlap (0.50) was observed in December. As a result, it seems that feeding spectrum of Indian halibut depends very little across seasons and size-classes. The small variation of the major prey groups among different months contributed to the high level of inter-month proportional overlap (Dulčić 2004).
The average RLG was measured as 0.043±0.01.
According to Biswas (1993), if RLG is <1, the fish is a carnivore. So, based on this theory, Indian halibut categorized as a carnivorous fish and as mentioned
before it is mainly a fish feeder. Carnivorous habit is also reported in other flatfish species (Castillo-Rivera et al. 2000).
In summary, Indian halibut is a piscivorous carnivore whose diet in the north of the Persian Gulf and Oman Sea consists of some nektons (bony fish and cuttlefish) and zoobenthos (shrimps and crabs).
Various indices of food preference showed that Teleostei were the most important and dominant prey group in the diet. However, diet composition showed no significant variation in relation to season, fish size and sex. Information of this study is important for fisheries management and understanding the trophic relationship of this species in relation to other species in the ecosystem. However, more comprehensive studies are needed to be conducted to understand the ontogenetic variations and also to determine the daily food consumption as well as a full perspective of Indian halibut within the context of the study area.
Acknowledgements
The authors are grateful to the staff of the marine biology & stock assessment department at the Persian Gulf and Oman Sea Ecological Research Institute for their help and providing the requisite facilities during this study. This research was funded by the University of Hormozgan.
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http://www.ijichthyol.org
هلاقم یشهوژپ
تاداع هیذغت
یا یهام کشفک نادندزیت
( Psettodes erumei )
رد لامش جیلخ
سراف و یایرد
نامع
یرهم هدازربنق
، 1
ناسحا ینارماک
*
، 2
فیرشدمحم ربجنر
، 1
یلع یروپرلااس
، 3
لراک زرتلاو
4
هورگ1
تسیز یسانش
،ایرد هدکشناد مولع و نونف
،ییایرد هاگشناد
،ناگزمره
،سابعردنب ناریا
.
هورگ2
،تلایش هدکشناد مولع و نونف
،ییایرد هاگشناد
،ناگزمره
،سابعردنب ناریا
.
هدکشهوژپ3
یژولوکا جیلخ سراف و یایرد
،نامع هسسؤم تاقیقحت مولع یتلایش
،روشک نامزاس تاقیقحت و شزومآ و جیورت
،یزرواشک
،سابعردنب ناریا
.
هورگ4
،تلایش هاگشناد شیتیرب
،ایبملک
،رووکنو اداناک
.
:هدیکچ
( نادنزیت کشفک یهام Psettodes erumei
ب ) ه ( نادندزیت نایهام کشفک هداوناخ هنوگ اهنت ناونع Psettodidae
بآ رد ) سراف جیلخ لامش( ناریا یبونج یاه
دروم هنوگ نیا ییاذغ تداع ،رضاح هعلاطم رد .تسا )نامع یایرد و هنومن .تفرگ رارق یسررب
ب اه ه هامرهم زا هناهام تروص 1395
هام نابآ ات 1396 لارت قیرط زا یاه
عمج )ناگزمره ناتسا( نامع یایرد و سراف جیلخ یلامش لحاوس دادتما رد هقطنم هس زا وگیم بورفک هدعم تایوتحم ،هنوگ نیا ییاذغ تداع یسررب تهج .دندش یروآ
433 زیلانآ هنومن ،دادعت نیا زا .دیدرگ
277
=ندوب یهت صخاش( دوب یلاخ هدعم 97
/ 63 دصرد ینعم توافت هک ) رد هیذغت تدش .داد ناشن هعلاطم هرود لوط رد ار یراد
هنومن دصرد نیرتشیب هک یسنج یگدیسر جوا نامز رد و لااب یسنج یگدیسر جوا زا لبق سنج ود ره رت یسررب .دوب نییاپ ،تشاد دوجو غلاب یاه
ناشن ییاذغ هریج بیک
ب نادندزیت کشفک یهام هک داد ه
یهام هنوگ کی هدمع روط ناوارف یناوختسا نایهام و تسا راوخ
مهم و نیرت صخاش( دوب هنوگ نیا ییاذغ هریج رد هورگ نیرت
رف یناوا
= روضح 08 / 48 دصرد =یبسن تیمها صخاش ، 44
/ 98 دصرد تخس .) ذغ هریج زا یکچوک شخب نایاپرس و ناتسوپ رف صخاش( دنداد لیکشت ار هنوگ نیا ییا
یناوا روضح
= بیترت هب 77
/ 5 و 92 / 1 دصرد
= بیترت هب یبسن تیمها صخاش( دندوب ادروخرب یرتمک تیمها زا و ) 33
/ 1 و 23 / 0 دصرد یصخشم توافت هنوگ نیا ییاذغ هریج بیکرت .)
توافت طقف و دادن ناشن تیسنج و یهام هزادنا ،لصف اب طابترا رد ار یاه
هورگ یددع دصرد و یناوارف دصرد رد ی هنوگ نیا یارب یفورت حطس .دش هدهاشم ییاذغ یاه
4 / 4
یم مهارف نادندزیت کشفک یهام هیذغت تداع دروم رد یئزج تاعلاطا هعلاطم نیا ،عومجم رد .دش هبساحم مهم هک دنک
تیریدم هنیمز رد تاعلاطا نیا تیمها نیرت
رد نینچمه و هنوگ نیا یریگیهام هیذغت شقن ک
هنوگ رگید اب طابترا رد نآ یا .تسا متسیسوکا یاه
تاملک :یدیلک یهام کشفک
، زیلانآ میژر
،ییاذغ تارییغت
،یلصف تیسنج .
