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Kenyaanse zeegrasvelden als voedselgronden voor de vroege levensstadia van belangrijke consumptievissen (Gerreidae en Lutjanidae) = Kenyan seagrass fields as feeding grounds for the early life stages of important consumption fish (Gerreidae and Lutjanidae)
Papadopoulos, I. (1995). Kenyaanse zeegrasvelden als voedselgronden voor de vroege levensstadia van belangrijke consumptievissen (Gerreidae en Lutjanidae) = Kenyan seagrass fields as feeding grounds for the early life stages of important consumption fish (Gerreidae and Lutjanidae). MSc Thesis. University of Gent, Zoology Institute, Marine Biology Section: Gent. 51 pp.
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Documenttype: Doctoraat/Thesis/Eindwerk
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Gerres acinaces Bleeker, 1854 [WoRMS]; Lutjanus argentimaculatus (Forsskål, 1775) [WoRMS]; Lutjanus ehrenbergii (Peters, 1869) [WoRMS]; Lutjanus fulviflamma (Forsskål, 1775) [WoRMS]
ISW, Kenia, Gazi Bay [Marine Regions]
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| Abstract |
This study, situated in Gazi Bay, Kenya, was aimed at describing the diet of juveniles of some commercially important tropical fish species and investigating whether the prey composition between different size classes within each species differed between sampling locations. The diet of following species was investigated: Gerres acinaces, Lutjanus argentimaculatus, L. fulviflamma en L. ehrenbergii. The ichthyofauna of the seagrass fields and the mangroves was sampled with a fine mesh ring net on the 17th and 18th of August 1993 (low tide). Ten stations were covered between the two main creeks of the bay. The analysed fish species were common in station 2 (mouth West Creek), 4 (in the West Creek), 8 (between West Creek and East Creek) and EC (in the East Creek). All these stations were marked by a dens seagrass vegetation. In total, 276 stomach analysis were conducted. All investigated fish were juveniles (standard lengths between 20 and 135mm) From stomach analysis it appeared that the smallest individuals of Gerres acinaces were somewhat selective feeders. Their diet was mainly composed of Harpacticoidea, added with Gammaridea and Tanaidacea. Expressed in gravimetric terms the harpacticids could be neglected in the diet and more energy-rich preys such as Polychaeta, Brachyura and Caridea were more important. Fish from larger size classes appeared to have a more varied diet were, next to Harpacticoidea, significant numbers of Oedicerotidae, Caridea, Gammaridae and Anthuridae were consumed. Heavy prey items such as crabs, Polychaeta, shrimp and Mysidacea provided enough energy. The diet of small (20-60mm) Lutjanus argentimaculatus was numerically mainly composed of Harpacticoidea; however, gravimetrically gammarid amphipods, Tanaidacea, shrimp, Caprellidae, Cheatognathae and crabs dominated the diet. Fish from larger size classes preferred Gammaridae and Tanaidacea. Other energetically important preys were Crangonidae, Brachyura, Caprellidae en Stomatopoda. Lutjanus fulviflamma and L. ehrenbergii had a more varied diet were numerically seen UCM, Brachyura, Caridea, Crangonidae and Stomatopoda dominated. Gravimetrically, the diet was composed only of crabs and shrimp. To calculate filling indices the animal prey and detritus in the stomachs of Gerres acinaces were looked at separately. The filling indices for detritus increased with the size of the fish, while the vullingsindices for the animal prey (for both Gerres acinaces and the Lutjanidae) were highest in the smaller size classes. Both numerical as gravimetrical stomach analyses data were analysed with multivariate statistical techniques. For Gerres acinaces the fish from station 2 and 4 were mostly separated, where the main prey in station 2 were Gammaridae and Tanaidacea and in station 4 were Harpacticidae. The fish of the smallest size classes from station 4 were mainly clustered. The fish from station 8 werediveided in both groups; their diet was characterized by both Gammaridae and Harpacticidae. All Lutjanus fulviflamma and L. ehrenbergii were clustered together en almost completely separated from L. argentimaculatus. The latter species preyed selectively on Harpacticoidea, Gammaridea and Tanaidacea. In contrast, L. fulviflamma and L. ehrenbergii and some L. argentimaculatus (with a standard length higher than 80 mm) appeared to have a more varied diet. |
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