The Morocco dentex,
Studies concerning the biological characteristics of
A detailed literature review shows that there is lack of research on the feeding regime of species distributed across the Mediterranean and Aegean Sea shores of Turkey. The presented study investigated the diet composition of the Morocco dentex along the Mediterranean and Aegean coast of Turkey. The purpose of this study was to identify the most important food groups for the Morocco dentex and to understand the seasonal selection of prey groups so that this information is available for comparisons with studies from other nearby or remote areas. We believe that the results of this study can be applied to the management of marine stocks in the investigated Mediterranean region for both the target species and other species competing for food in the same habitat.
The mean total length (cm) and the number of individuals (N) examined separately in autumn, winter, spring and summer were as follows: 14.32 cm – 47, 12.49 cm – 78, 13.29 cm – 50 and 12.46 cm – 55, respectively.
The fish were dissected immediately after collection. Their stomachs were removed and stored in formalin (10%) until the contents could be analyzed. The stomach contents were homogenized in petri dishes and then examined using an SZX7 Olympus stereo microscope at 0.8 to 5.6× (zoom) and 10× resolution. Prey items were identified to the nearest possible taxon.
Once counted, individuals of the same species were weighed together (wet weight to the nearest ± 0.0001 g) after excess moisture was removed by blotting the prey items on the tissue paper. The following indices were used to quantify the importance of different prey items in the diet of the percentage frequency of occurrence (F%) = the number of stomachs in which a food item was found, divided by the total number of non-empty stomachs, multiplied by 100 (for each prey group computed separately). the percentage numerical abundance (N%) = the number of each prey item in all non-empty stomachs, divided by the total number of food items in all stomachs, multiplied by 100. the percentage gravimetric composition (W%) = wet weight of each prey item, divided by the total weight of stomach contents, multiplied by 100 (Hyslop 1980).
The main food items were identified using the index of relative importance (IRI) of Pinkas et al. (1971):
the index was expressed as follows:
The percentage of empty stomachs to the total number of examined stomachs was expressed as the vacuity index (VI), where VI% = 100 × (the number of empty stomachs/the number of examined stomachs). The Biodiversity Professional (Version 2) software was used to determine the seasonal diversity of consumed catches (Shannon index), the richness (Margalef index) and similarity (Bray-Curtis). In the assessment of the Shannon index results, the following ranges were applied: 0-1 = a low level of diversity, 1-3 = a medium level of diversity and 3-5 = a high level of diversity (Washington 1984).
During the study period, a total of 230 specimens of the Morocco dentex were examined, and it was found that 216 stomachs of that total number were full. Whereas the stomach fullness index was estimated at 93.9%; the highest seasonal stomach fullness index was determined in the winter – 96.2%. This was followed by the autumn (95.7%), spring (92.0%) and summer (90.9%), respectively.
Following the examination of the contents of full stomachs, it was found that the species feeds mainly on three major prey groups: Crustacea, Mollusca and Teleostei (Table 1). As evidenced by the frequency of occurrence, numerical composition, gravimetric composition and the index of relative importance, Crustacea was determined as the most important prey group. Mollusca were the second prey group in terms of the numerical amount and frequency of occurrence, whereas Teleostei were the second group in terms of the weight method (Fig. 1).
Seasonal diet composition of
Winter |
Autumn |
Spring |
Summer |
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Prey groups | N% | F% | W% | IRI% | N% | F% | W% | IRI% | N% | F% | W% | IRI% | N% | F% | W% | IRI% |
Crustacea | ||||||||||||||||
Amphipoda | 19.30 | 29.33 | 0.14 | 7.63 | 16.67 | 40.00 | 0.45 | 8.86 | 8.33 | 8.70 | 0.89 | 0.92 | 5.88 | 10.00 | 0.27 | 0.84 |
Brachyura | 5.61 | 21.33 | 22.29 | 7.96 | 8.89 | 40.00 | 17.08 | 13.44 | 6.25 | 8.70 | 23.46 | 2.96 | - | - | - | - |
Decapod crustaceans | 28.77 | 81.33 | 31.91 | 66.00 | 27.78 | 86.67 | 14.91 | 47.86 | 47.92 | 82.61 | 46.72 | 89.65 | 47.06 | 80.00 | 6.47 | 58.38 |
Isopoda | 7.72 | 20.00 | 1.30 | 2.41 | 11.11 | 33.33 | 0.91 | 5.18 | 2.08 | 4.35 | 3.55 | 0.28 | - | - | - | - |
Mysidacea | 21.40 | 42.67 | 2.24 | 13.49 | 22.22 | 53.33 | 1.13 | 16.11 | 10.42 | 13.04 | 1.63 | 1.80 | 29.41 | 30.00 | 1.20 | 12.52 |
Ostrocoda | 1.40 | 5.33 | 0.32 | 0.12 | 1.11 | 13.33 | 12.23 | 2.30 | 2.08 | 4.35 | 0.36 | 0.12 | - | - | - | - |
Copepoda | ||||||||||||||||
|
0.35 | 1.33 | 0.08 | 0.01 | 1.11 | 6.67 | 0.12 | 0.11 | - | - | - | - | - | - | - | - |
|
0.35 | 1.33 | 0.52 | 0.02 | - | - | - | - | - | - | - | - | - | - | - | - |
|
0.70 | 2.67 | 0.61 | 0.05 | - | - | - | - | - | - | - | - | - | - | - | - |
|
0.35 | 1.33 | 20.80 | 0.38 | 1.11 | 6.67 | 31.88 | 2.84 | - | - | - | - | - | - | - | - |
Calanoida | 2.46 | 8.00 | 0.66 | 0.33 | 2.22 | 13.33 | 0.29 | 0.43 | 2.08 | 4.35 | 0.64 | 0.14 | - | - | - | - |
Parazitic copepoda | 0.35 | 1.33 | 0.39 | 0.01 | - | - | - | - | - | - | - | - | - | - | - | - |
Harpacticoida | 1.75 | 6.67 | 0.20 | 0.17 | - | - | - | - | - | - | - | - | - | - | - | - |
Mollusca | ||||||||||||||||
Pteropoda | 6.32 | 1.33 | 0.30 | 0.12 | 3.33 | 6.67 | 0.91 | 0.37 | - | - | - | - | - | - | - | - |
Gastropoda | - | - | - | - | - | - | - | - | 14.58 | 8.70 | 14.84 | 2.93 | 5.88 | 10.00 | 6.17 | 1.64 |
Bivalvia | 2.11 | 8.00 | 0.77 | 0.31 | 2.22 | 13.33 | 2.26 | 0.77 | 2.08 | 4.35 | 2.35 | 0.22 | - | - | - | - |
Teleostei | 1.05 | 4.00 | 17.44 | 0.99 | 2.22 | 6.67 | 17.83 | 1.73 | 4.17 | 8.70 | 5.56 | 0.97 | 11.76 | 20.00 | 85.88 | 26.62 |
Percentage numerical composition (N%), frequency of occurrence (F%), percentage gravimetric composition (W%) and the percentage index of relative importance (IRI%) of the main prey groups for
According to the detailed stomach content analysis, the species feeds on 17 different prey groups. Of these prey groups, the ones represented by an IRI value equal to or greater than 1% are decapod crustaceans (IRI% = 71.5), Mysidacea (IRI% = 9.8), Brachyura (IRI% = 7.8), Amphipoda (IRI% = 5.7), Isopoda (IRI% = 2.1) and Teleostei (IRI% = 1.8). Other prey groups are represented by IRI values below 1% (Fig. 2).
Percentage index of relative importance (IRI%) of prey groups for
In terms of N%, F% and W% values, decapod crustaceans proved to be the most abundant. In terms of the W% value, this prey group was followed by Brachyura, Teleostei and others. In terms of the F% value, it was followed by Mysidacea, Amphipoda, Brachyura, Isopoda and other prey groups (Fig. 3).
Diet composition of
When seasonal consumed prey group diversity (Shannon index, Shannon Hmax Log Base 10) based on IRI% values was taken into consideration, it was found that winter (1.204), autumn (1.079) and spring (1.000) seasons were characterized by a medium level of diversity, while the summer season (0.699) – by a low level of diversity. On the other hand, the richness of the prey group consumed by this species was the same for all seasons (Margalef index, Margalef M Base 10 = 8). Therefore, it can be concluded that the prey group richness does not differ in respect of the seasons. According to the Bray-Curtis clustering analysis, the similarity between the top and the bottom prey groups was 81.6% in the winter and autumn seasons and 55.3% in the autumn and spring seasons. There were two different groups at the 75% similarity threshold. While autumn, winter and spring seasons constituted a group on one side, the summer season constituted a group on the other side (see Fig. 4).
Dendrogram of the cluster analysis showing the diet similarity (IRI%) in relation to seasons, using the Bray-Curtis index
Feeding occurs daily for most fish and may be the most frequent voluntary activity (Bond 1996). It is generally stated that the feeding intensity in fish decreases during the spawning season (Nikolsky 1976). Our findings were consistent with this statement. The Morocco dentex spawns in the spring and summer months in the Mediterranean (Bauchot & Hureau 1986). In line with this, we observed the largest number of empty stomachs in the summer.
In another detailed study of the diet composition of this species, the stomach contents of 1281 samples from 4 different stations were examined, and the empty stomach rate was determined to be 60% (Nguyen & Wojciechowski 1972). The findings of that research suggested that the species has a lower stomach fullness rate on the Senegal shelf. A larger number of fish samples might have resulted in a higher empty stomach rate. Moreover, it is believed that the poorer Atlantic waters, in comparison with the Aegean Sea, would result in higher empty stomach rates for this species.
In the study conducted on the Senegal shelf during the winter season only, which displays a significant similarity with this study, and based on the diet composition analysis, four major prey groups were found in the stomach content of the species: Crustacea, Teleostei, Polychaeta and Mollusca (Nguyen & Wojciechowski 1972). Of the groups caught, only the Polychaeta group was not found in our study. However, it was reported in other studies in relatively insignificant amounts compared to other taxa and determined by the weight method. This may be due to the smaller population in our study. However, Polychaeta were found and reported in the diet composition of a number of fish species in recent decades along the Aegean Sea shores of Turkey (Sever et al. 2005; Sever et al. 2006; Sever et al. 2009; Bayhan et al. 2009; Bayhan & Sever 2009 and Bayhan et. al. 2013).
According to all index values used in this study, the primary prey group was Crustacea. Similarly, in terms of weight, Crustacea (especially Paguridae, Galatheidae, Brachyura and Cirripedia) accounted for 60% of all prey. Our findings showed that fish is the second prey group, accounting for 20% of the total prey weight. In addition, other similar studies have reported that this group was followed by other prey groups, such as Polychaeta, Gastropoda, Mysidacea and Amphipoda (Nguyen & Wojciechowski 1972). A review of the existing literature has shown that
Body shape is clearly an important part of the mechanism for bringing the predator close enough to the prey or food item for it to be consumed (Horn & Ferry-Graham 2006). Also in many fish species, morphological similarity can be considered as a proxy for similarities in the habitat use. The Sparidae family includes species that are recognized for common morphological features such as the structure and positioning of the fins and for specialized dentition.