J. Mar. Biol. Ass. U.K. (2005), 85, 1533^1534 Printed in the United Kingdom
Diet and diel feeding activity of juvenile pompano (Trachinotus ovatus) (Teleostei: Carangidae) from the southern Adriatic, Croatia Mirna Batistic¤*P, Pero Tutman*, Dubravka Bojanic¤*, Bosko Skaramuca*, Valter Kozul*, Niksa Glavic¤* and Vlasta Bartulovic¤O *Institute of Oceanography and Fisheries-Split, Laboratories Dubrovnik, Kneza D. Jude 12, PO Box 83, 20001 Dubrovnik, Croatia. O Department for Aquaculture, University of Dubrovnik, C¤ira Caric¤a 4, 20 000 Dubrovnik, Croatia. P Corresponding author, e-mail:
[email protected]
Food and feeding activity of juvenile pompano Trachinotus ovatus (25^97 mm) collected in the summer ^ autumn in 2003 in coastal shallow-water bays in the south-eastern Adriatic were examined. Juvenile pompano were exclusively daytime feeders and fed in the entire water column, from surface to bottom taking not only plankton, but benthic and terrestrial species as well. Of 18 prey taxa identi¢ed, crustaceansparticularly copepodswere the major group, followed by benthic foraminiferans and insects. Feeding on benthic species is reported for the ¢rst time in this study.
Members of the genus Trachinotus have attracted particular attention as candidates for mariculture. This has led to investigations of their feeding habits, both under controlled conditions and in nature (see Helmer & Teixeira, 1995; Tutman et al., 2004). Few data yet are available on the natural diet of Trachinotus ovatus L. 1758, which presents some general aspects of the diet of individuals collected in the eastern Atlantic (Moreno & Castro, 1995) and along the Mediterranean coastline of Israel (Chervinski & Zorn, 1977). The objective of this study was to investigate the feeding ecology of this species, with special attention paid to the food composition and diel feeding activity of juveniles from the south-eastern Adriatic Sea. Juvenile pompano were collected in July, August and October in 2003 at two localities along Croatia’s south-eastern coast: Prapratna Bay (428330 N 188250 E) and Lopud (428390 N 178550 E), at a depth of 3 m. Fish were collected with a 25 m beach-seine net on a sandy bottom. The samples were collected at 4-h intervals over 24-h periods (see Figure 1). The duration of each catch was approximately 20 min. The ¢sh were preserved in 5% formalin immediately after capture. Total length (TL) and body weight (BW) of each specimen was measured to the nearest 0.1mm and 0.01g, respectively, prior to dissection for stomach removal. Stomach contents were identi¢ed to the lowest taxon possible using a stereomicroscope. Quanti¢cation of stomach contents was based on the number of all identi¢able prey and wet weight (with an accuracy of 0.0001g) of major prey (numerous small prey and rare heavy prey). The remains of prey comprised telsa, jaws, head, etc. and were accounted according to the recommendation of Pais (2002). The Fullness Index (%FI) the percentage ratio of the weight of stomach contents to the ¢sh’s total body weight, and the vacuity index (%V) the percentage ratio of the empty and nearly empty stomachs to total number of stomachs analysed, were used to characterize feeding state. The percentage frequency of occurrence (%F), percentage composition by number (%PN) and by weight (%W) of prey categories were calculated in order to provide indices of importance by number (IN) and by wet mass (IW) as follows: IN¼(%PN6%F)1/2; IW¼(%W6%F)1/2 (see Moreno & Journal of the Marine Biological Association of the United Kingdom (2005)
Castro, 1995). An index of global importance (IG) avoids exaggerating the importance of the numerous small-sized prey or of the rare heavy prey in numerical and gravimetrical methods (see Moreno & Castro, 1995) and is expressed as follows: IG¼(IN+IW)/2. Juvenile ¢sh with food in their stomach were divided into three length fractions: small (20^ 40 mm), medium (40^60 mm), and large (460 mm), including 33, 29 and 19 individuals, respectively. Analysis of similarities (ANOSIM) was used to test whether the diet in three sizeclasses of ¢sh di¡ered statistically. Similarity percentages (SIMPER) was used to determine which food categories were responsible for di¡erences between size-classes. These statistical analyses were performed using PRIMER 5 software packages. A total of 173 juvenile pompano was collected. Total length and BW of all juveniles ranged from 25 to 97 mm (mean 45+14 mm) and 0.15 to 6.70 g (mean 1.00+1.01g), respectively. The mean fullness index was highest during the day (0800, 1200, 1600 h). Contrarily, feeding activity almost stopped after 2000 with highest vacuity index at 2400 h (Figure 1). Both experimental (Tutman et al., 2004) and ¢eld studies have documented that juvenile pompano are diurnal feeders. This is of particular importance for aquaculture purposes.
Figure 1. Vacuity index (V%) and mean fullness index (FI%) of juvenile pompano stomachs versus time of day. (Error bars represent standard deviations, + of mean FI%).
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Diet and diel feeding activity of juvenile pompano
Table 1. Frequency of occurrence (%F) of all prey categories and index of importance (%) of major prey items by number (IN), wet mass (IW) and global (IG) in stomachs of juvenile Trachinotus ovatus. PREY
%F
ZOOPLANKTON Hydromedusae 3.0 Siphonophora 1.8 Pteropoda 4.3 Bivalvia larvae 11.4 Chaetognatha 8.6 Cladocera 42.1 Penilia spp. 30.4 Evadne spp. 14.5 Ostracoda 29.0 Conchoecia spp. 29.0 Copepoda 100.0 nauplii 12.0 Harpacticoida Microsetella spp. 24.6 Euterpina acutifrons 63.8 Calanoida Unidenti¢ed copepodites & small adults 87.0 Paracalanidae & Clausocalanidae 29.0 Acartia spp. 29.0 Temora stylifera 45.5 Candacea spp. 3.0 Cyclopoida Oithona spp. 45.0 Sapphirina spp. 2.0 Corycaeus spp. 61.0 Poecilostomatoida Oncaea spp. 96.0 Euphausiacea 8.6 Mysidacea 5.8 Isopoda 8.6 Amphipoda 40.0 Decapoda larvae 30.0 Crustacea remains 40.0 Tunicata 7.2 Appendicularia 7.2 Doliolida 1.0 Fish larvae 7.2 Unidenti¢ed ¢sh eggs 11.0 BENTHIC FORAMINIFERA BENTHIC POLYCHAETA INSECTA Hymenoptera Other insects
27.0
IN
IW
IG
2.4 1.4 10.3
4.6 3.0 7.4
3.5 2.2 8.9
6.8
7.0
6.9
83.0
59.8
71.4
1.1 1.0 1.0 7.8 4.6
3.2 4.1 2.1 28.1 6.3
2.2 2.6 1.6 17.9 5.4
0.7 8.0
2.6 13.4
1.7 10.7
20.3
15.1
17.7
5.4
27.7
16.6
6.0 41.1 40.0 3.5
Eighteen di¡erent taxonomic groups of prey were identi¢ed (Table 1). Phytoplankton (Ceratium sp.) was found in only one stomach, and this may be a case of incidental ingestion. The main food, however, was crustacea, particularly copepods (IG¼71.4%) occurring in all stomachs containing food (Table 1). Small adults and copepodites belonging to Calanoida
Journal of the Marine Biological Association of the United Kingdom (2005)
families and species of Cyclopoida, Poecilostomatoida, and Harpacticoida were most prevalent (Table 1). Amphipods were next, with an IG of 17.9%. Non-planktonic prey benthic foraminiferans and insects were also important food for juvenile pompano. Insects usually were present in amounts of from 1 to 3 individuals, while forams appeared in aggregations of generally more than 100 shells. Both had similar IGs, 16.6 and 17.7%, respectively (Table 1). Feeding by juvenile pompano on benthic species was observed for the ¢rst time in this study. The diet of juvenile pompano, based on crustacean and insects, was also found by Chervinski & Zorn (1977) along the Mediteranean coastline of Israel. Moreno & Castro (1995) found a similar diet for juvenile pompano from the Canary Islands, but with a higher contribution of insects. Without data on the actual abundance of food during the investigated period, no explanation can be advanced regarding the choice of prey by these ¢sh. However, statistically signi¢cant di¡erences between the diet of small (20^ 40 mm) and large (460 mm) categories of ¢sh was showed (ANOSIM, P50.01). According to SIMPER analysis, the prey most responsible for di¡erences between these categories were: forams and large crustaceans. Benthic forams (0.3^0.4 mm), especially important for the smallest ¢sh, suggest that they prefer not only smaller, but also less-mobile, prey. These ¢ndings could be the base for further investigation in order to determine the role of the juvenile pompano in the food web of shallow coastal waters, considering the fact that they are taking not only plankton, but benthic and terrestrial species as well. We wish to thank Professor Dr Frano Krsinic for identi¢cation of benthic foraminifers and Dr Nenad Jasprica for the phytoplankton.
REFERENCES Chervinski, J. & Zorn, M., 1977. Note on occurrence and the food of juvenile kachlan (Trachinotrus ovatus, Linnaeus (Pisces, Carangidae)) from the Mediterranean. Aquaculture, 10, 175^ 185. Helmer, J.L. & Teixeira, R.L., 1995. Food habits of young Trachinotus (Pisces, Carangidae) in the inner surf-zone of a sandy beach of Southeastern Brazil. Atlantica. Rio Grande, 17, 95^107. Moreno, T. & Castro, J.J., 1995. Community structure of the juvenile of coastal pelagic ¢sh species in the Canary Islands waters. Scientia Marina, 59, 405^413. Pais, C., 2002. Diet of deep-sea ¢sh, Haplostethus mediterraneus, from the coast of Portugal. Journal of the Marine Biological Association of the United Kingdom, 82, 351^352. Tutman, P., Glavic, N., Kozul, V., Skaramuca, B. & Glamuzina, B., 2004. Preliminary information on feeding and growth of pompano, Trachinotus ovatus (Linnaeus, 1758) (Pisces, Carangidae) in captivity. Aquaculture International, 12, 387^393.
Submitted 26 January 2005. Accepted 28 June 2005.
