Gerres Oyena Research Articles

Spatio-temporal variations of fish assemblages in seagrass ecosystem of Karang Congkak Island, Kepulauan Seribu

Seagrass are globally known as an essential habitat for marine fishes. The study of fish assemblages in seagrass ecosystem is needed as the first base to select the most suitable coastal fisheries management. The study aims to reveal the composition of fish assemblages both seasonally and spatially in Karang Congkak Island, Kepulauan Seribu. Sampling was performed six times in NW monsoon (March), first transitional monsoon (April-May) and SE monsoon (Juni, August, September) 2018. Fish were sampled at four sites at seagrass ecosystem of Karang Congkak Island, namely eastern, southern, western, and northern by using beach seine net. The differences of juvenile fish assemblages were analyzed using One-Way ANOSIM. A total of 6,326 fish were collected belonging to 78 species, 31 families and 10 orders in which Labridae was the most diverse family. The result indicates strong spatial and temporal variation in fish composition. Fish compositions were dominated by juvenile both spatially and temporally. The most common species that inhabits seagrass beds of the Karang Congkak Island as temporary resident such as Gerres oyena and Siganus canaliculatus, and regular visitor namely Halichoeres argus. Cannonical correspondence analysis indicated strong correlation between several fish species and environmental variables.

The complete mitochondrial genome sequence of Gerres filamentosus (Perciformes: Gerridae)

The complete mitochondrial genome of Gerres filamentosus was sequenced by high throughput sequencing method. Length of this genome is 16,795 bp, containing 13 protein-coding genes, 22 tRNA genes, two rRNA genes and one large non-coding region. ND6 and eight tRNA genes are encoded by L-strand, and others are encoded by H-strand, which is similar to those in most vertebrates. Phylogenetic tree based on 13 protein-coding genes shows that the clade of G. filamentosus is closely clustered with that of Gerres oyena, and families Caproidae and Ephippidae have the closest relationship to Gerridae, comparing with Sillaginidae

Rare parasitic copepods (Siphonostomatoida: Lernanthropidae) from Egyptian Red Sea fishes.

Two rare species of parasitic copepods belonging to the genus Lernanthropus de Blainville, 1822 (Siphonostomatoida: Lernanthropidae) are redescribed in detail, based on material collected from Red Sea fishes, caught at El-Tor, near Sharm El-Sheikh on the Red Sea coast of Egypt. Adult females of Lernanthropus sanguineus Song & Chen, 1976 were found on the gills of snapper Lutjanus fulviflamma (Forsskål). This species was known only from its original description based on material from Chinese waters. Adult females of Lernanthropus triangularis Pillai, 1963 were obtained from the gills of mojarra Gerres oyena (Forsskål). Both parasite species are new records for Egyptian Red Sea waters and both host records are new.

Parasitic copepods from Egyptian Red Sea fishes: Bomolochidae Claus, 1875.

Two species of parasitic copepods from the genus Bomolochus von Nordmann, 1832 (Cyclopoida: Bomolochidae) are redescribed in detail, based on material collected from the gills of Red Sea fishes. Host material was caught at El-tor, near Sharm El-Sheikh, and in the Gulf of Suez, Egypt. Both sexes of Bomolochus bellones Burmeister, 1835 were collected from the gills of a needlefish Tylosurus choram (Rüppell) caught in the Gulf of Suez. This is a new host record. The female is well characterised so only the male is described. Adult females of Bomolochus minus Lin & Ho, 2005 were obtained from the branchial cavities and gills of mojarra Gerresoyena (Forsskål). This species was known only from its original description in Taiwan, and this report constitutes a new host record and a significant range extension. Both parasite species are new records for Egyptian Red Sea waters.

Bioaccumulation of metals in fish species from water and sediments in macrotidal Ennore creek, Chennai, SE coast of India: A metropolitan city effect

Accumulation of trace metals (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd) were investigated in water, sediment (n=20) along with six fish of diverse feeding guilds (Sillago sihama, Liza parsia, Etroplus suratensis, Oreochromis mossambicus, Arius parkii and Gerres oyena) from the Ennore creek, northern part of Chennai metropolitan megacity, southeast coast of India. Dissolved trace metals (DTMs) in surface water samples and total trace metals (TTMs) in surface sediments (top 0–10cm) indicate that concentration pattern of metals was higher in the discharge point of the river/channels entering the main creek. The maximum mean values of DTMs exhibited the following decreasing order (expressed in µg/L): Fe (1698)>Mn (24)>Zn (14.50)>Pb (13.89)>Ni (6.73)>Cu (3.53)>Co (3.04)>Cr (2.01) whereas the trend is somewhat different in sediments (µgg−1): Fe (4300)>Mn (640)>Cr (383)>Zn (155)>Cu (102)>Ni (35)>Pb (32)>Cd (0.51) are mainly due to the industrial complexes right on the banks of the river/channels. Species-specific heterogeneous patterns of tissue metal loads were apparent and the overall metal enrichment exhibited the following decreasing order (expressed in µgg−1): Cu (7.33)>Fe (6.53)>Zn (4.91)>Cr (1.67)>Pb (1.33)>Ni (0.44)>Mn (0.43)>Co (0.36)>Cd (0.11). This indicates that metals are absorbed onto the different organs, which is also endorsed by the calculated values of bioaccumulation factor (BAFs) (avg. muscle 117, gill 126, liver 123, intestine 118) in fishes. The high calculated biota sediment accumulation factor (BSAF) (0.437) for the species Arius parkii is considered to be a potential bioindicator in this region. The enrichment of trace metals is also supported by the association of metals in water, sediments and different body organs (muscle, gill, liver, intestine) of fish samples. Comparative studies with other coastal regions indicate considerable enrichment of DTMs & TTMs in sediments as well as in various organs of fish samples. Holistic spatial, temporal monitoring and comprehensive regional strategies are required to prevent health risks and ensure nutritional safety conditions.

Seasonality in fish assemblage structure in an East African mangrove creek

The spatial and seasonal structures of fish assemblages in a tropical mangrove tidal creek, Tudor, Kenya, were analysed from monthly survey data, extending from October 2007 to July 2008, and covering the north-east (NEM; October–March) and south-east (SEM; April–July) monsoon seasons. A total of 2 118 individuals, representing 84 species belonging to 49 families, were caught. Gerres oyena, Terapon jarbua and Lutjanus fulviflamma were the dominant species in all seasons. There was within-creek seasonal variability in species abundance and diversity. Overall, the mean density (individuals m–2) was higher during the SEM season (0.368; SE 0.078) than the NEM season (0.255; SE 0.041). The NEM season had significantly more species (n 69) than the SEM season (n 63) (χ2 = 317.891, p < 0.0001). Two-way ANOVA indicated the influence of season and habitat on abundance of some species. The abundance of creek-resident species was significantly influenced by site whereas abundance of creekdependent and transient species was influenced by interaction between seasons and stations. Bray-Curtis cluster analysis defined two species assemblages, reflecting differences in temporal and spatial use of the creek by the fish species. Correspondence analysis indicated that seasonal fish assemblages were only distinct at the mouth of the creek with less clear seasonal structure in the upper region of the creek.

Molecular comparison of geographically extreme populations of fish species of wide Indo-Pacific distribution

A total of six Red Sea inshore fish species with wide Indo-Pacific distribution, including Lessepsian migrants that reached the Mediterranean Sea via the Suez Canal, were studied and compared genetically to conspecific populations from Japan and the Seychelles. Examination of the cytochrome c oxidase 1 (COI) gene of Apogon cyanosoma, Sargocentron rubrum, Upeneus moluccensis, Spratelloide sdelicatulus, Gerres oyena and Terapon jarbua from Japan, the Red Sea, the Seychelles and the Mediterranean revealed that in five out of six fish species, a difference greater than 4% was found. These results indicate the importance of DNA genetic analysis in revealing possible cryptic species and supplementing classic taxonomic studies, as well as contributing to a reappraisal of the zoogeography and evolution of Indo-Pacific ichthyofauna and enhancing our understanding of fish biodiversity.

Gut Content Analysis of Selected Commercially Important Species of Coral Reef Fish in the Southwest Part of Iligan Bay, Northern Mindanao, Phillippines

The diet composition of selected economically important reef fishes was described. Sampling for fish and plankton was done every month from July to December 2004 in eight sampling stations located in Maigo and Kauswagan, lanao del Norte. Nine fish species were selected for the gut content study. The nine species belong to seven families: the Gerreidae (Gerres oyena), Leiognathidae (Leiognathus splendens), Lethrinidae (Lethrinus insulindicus), Scaridae (Scarus bowersi), Siganidae (Siganus guttatus and Siganus vermiculatus), Theraponidae (Therapon jarbua and Therapon sp.) and Mullidae (Upeneus caeruleus). The result of the stomach or gut content analysis showed that majority of the fish species preyed on zooplankton and benthic animals. These fishes were categorized as generalist species based on Costello's method. They are represented by Gerres oyena, Leiognathaus splendens, Lethrinus insulindicus, Therapon jarbua, Therapon sp. and Upeneus caeruleus except for fishes belonging to Family Scaridae (Scarus bowersi) and Family Siganidae (Siganus guttatus and Siganus vermiculatus) which exclusively fed on algae and were categorized as strict herbivores. A total of 46 zooplankton groups were identified and 76.51% of the total population was composed of copepods which included calanoida, cyclopoida, harpacticoida, copepod nauplius and eggs. Comparison between the abundance of zooplankton between stations in Maigo, and Kauswagan, Lanao del Norte showed no significant difference (p > 0.05) in both areas. This study showed that out of the nine economically important reef fishes, six fish species preferred to prey on zooplankton species. This further showed that despite the abundance of zooplankton in the environment, planktivorous fishes preferred to prey on some zooplankton groups like copepods, amphipods and crab megalopa. Hence, zooplankton as prey of selected economically important reef fishes should be conserved and harvesting of commercial fishes should be controlled.

Spatial and seasonal variations of fish assemblages in mangrove creek systems in Zanzibar (Tanzania)

Spatial and seasonal variations of fish assemblage composition were studied in three non-estuarine mangrove creeks of Zanzibar (Tanzania). Fish were collected monthly for one year at three sites (lower, intermediate and upper reaches) in each creek using a seine net (each haul covering 170 m 2). Density, species number and diversity of fish were all higher at sites with dense cover of macrophytes (seagrass and macroalgae) than over unvegetated sandy sites. In general, fish assemblages mainly comprised juveniles of a few abundant taxa, e.g. Mugil cephalus, Mugilidae spp. and Leiognathus equulus at sites with mud substratum and Gerres oyena, Lethrinus harak and Sillago sihama at sites dominated by macrophytes. Multivariate analyses revealed significant separations in fish assemblage composition within the two creeks where the bottom substratum differed among sites. Overall, season seemed to have little effect on density, species number, diversity index ( H′) and assemblage structure of fish. Water condition variables were also relatively stable across the season, although a short-term fluctuation primarily induced by decreased salinity, occurred during the heavy rains in April and May. Fish assemblage structure was not significantly affected by any of the abiotic factors tested. However, significant regressions were found between the other fish variables and environmental variables, but since these associations were mostly species-specific and generally inconsistent, we suggest that the overall distribution patterns of fish were mainly an effect of particular substrate preferences of fish species rather than contemporary water conditions.

Reproductive Biology of Gerres Oyena (Pisces: Gerreidae) Along the Bagamoyo Coast, Tanzania

The reproductive biology of Gerres oyena (Forskal, 1775) (Gerreidae) along the Bagamoyo coast was studied from January to December 1999 using samples from monthly commercial catches. Size at first maturity was 12.8 and 13.9 cm TL for males and females respectively. The sex ratio was found to be 0.98:1 (m:f) and was not significantly different from 1:1. G. oyena spawns throughout the year with two peaks: one in March and the other between October and December, which coincide with the northeast monsoon. Ova-diameter frequency distributions indicated that G. oyena is a multiple spawner. They may spawn in three successive batches within the same prolonged spawning season. On an average, the numbers of mature ova produced were 148,138 per fish. For management purposes, a focus should be on the size of maturation relative to length-body depth or capture size. This would reduce harvesting of pre-reproductive individuals.

Fish assemblages in Tanzanian mangrove creek systems influenced by solar salt farm constructions

Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each haul covering 170 m 2) within three locations in each creek, i.e. at the upper, intermediate and lower reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation, whereas there were no differences among the three sites in the undisturbed mangrove creek system. In addition, multivariate analyses showed that the structure of fish assemblages varied between forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across the season, we found no significant differences except for a tendency of a minor increase in fish densities during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops machnata, which were both found in relatively low abundances compared to the undisturbed areas. The conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm developments will decrease fish densities, biomass and species numbers as well as alter the overall fish assemblage composition in the salt farm area but not downstream in the creek.

Abundance and Diversity of Coral Reef Fish Larvae at Hurghada,Egyptian Red Sea

he larvae of coral reef fishes have been studied in Hurghada at the Egyptian Red Sea on exposed and sheltered inshore and offshore sites. Ichthyoplankton samples were taken by plankton net of 0.5 mm mesh size on a monthly basis from January to December 2005. The total abundance of fish larvae at all sites was 1993/1000m 3 . There were significant differences in larval abundance between sites and months. The sheltered inshore site (H3) showed a significantly higher abundance of all sites, whereas the exposed inshore Abu Sadaf site had the lowest abundance. The most abundant 10 taxa were Atherinomorus lacunosus (Atherinidae), Spratelloides delicatulus (Clupeidae), Gerres oyena (Gerreidae), Hypoatherina temmincki (Atherinidae), Petroscirtes mitratus (Blennidae), Vinciguerria mabahiss (Phosichthyidae), Enneapterygius sp. (Triptrygiidae), Mulloides flavolineatus (Mullidae), Benthosema pterotum (Myctophidae) and Gobiidae, forming about 82.5% of all collected larvae. The most dominant species was Atherinomorus lacunosus, contributing 1٩% of all taxa with a total abundance of ١١٣ larvae/1000m 3 . Larvae of families Siganidae and Soleidae were the least abundant both with 0.23 larvae/1000m 3

Reproductive biology of common silver biddy Gerres oyena in Okinawa Island of southern Japan

Common silver biddy Gerres oyena were collected monthly between November 2002 and November 2005 in Okinawa Island of southern Japan. The seasonal reproductive cycle of this species was investigated using the gonadosomatic index (GSI) and through histological observation of gonads. Temporal variation in the GSI reflected gonadal development from histological observations; ovary development occurred from March to September and testes development occurred between March and August. Maximal development was observed in April and May in both sexes. While mean values for hepatosomatic and lipidosomatic indices decreased markedly in females relative to males during gonadal development, mean condition factors decreased with gonadal recrudescence in both sexes. The minimum standard length (SL) at sexual maturity was 89.7 mm for females and 81.4 mm for males and the size at which 50% of individuals were sexually mature was 104 and 92 mm SL in females and males, respectively. The power relationships of batch fecundity (BF) versus standard length (SL, mm) and body weight (BW, g) of females can be expressed as BF=46.7×e1.64SL and BF=19 697×e0.49BW , respectively.

Habitat use patterns of fishes across the mangrove-seagrass-coral reef seascape at Ishigaki Island, southern Japan

To clarify seascape-scale habitat use patterns of fishes in the Ryukyu Islands (southern Japan), visual censuses were conducted in the mangrove estuary, sand area, seagrass bed, coral rubble area, branching coral area on the reef flat, and tabular coral area on the outer reef slope at Ishigaki Island in August and November 2004, and May, August and November 2005. During the study period a total of 319 species were observed. Species richness and abundance were highest in the branching and tabular coral areas, followed in order by the seagrass bed and mangrove estuary, and coral rubble and sand areas, in each month. Cluster analysis resulted in a clear grouping of assemblage structures by habitat type rather than by census month. SIMPER analysis showed that fish assemblages in the tabular coral area were mainly characterized by Acanthurus nigrofuscus, Pomacentrus lepidogenys, P. philippinus and P. vaiuli, the branching coral area by Chromis viridis and Pomacentrus moluccensis, the coral rubble area by Amblyeleotris steinitzi and Ctenogobiops pomastictus, the seagrass bed by Cheilio inermis, Lethrinus atkinsoni and Stethojulis strigiventer, the sand area by Valenciennea longipinnis, and the mangrove estuary by Gerres oyena, Lutjanus fulvus and Yongeichthys criniger. Moreover, fishes exhibited two habitat use strategies, inhabiting either a single or several specific habitats throughout their benthic life history stages, or having a possible ontogenetic habitat shift from the mangrove estuary or seagrass bed to coral-dominated habitats (e.g., Lethrinus atkinsoni, Lethrinus obsoletus, Lutjanus fulviflamma, Lutjanus fulvus, Lutjanus gibbus, Lutjanus monostigma and Parupeneus barberinus), suggesting that the mangrove estuary and seagrass bed have a nursery function.

Trophic Ecology of Some Common Juvenile Fish Species in Mtwapa Creek, Kenya

The trophic status of common fish species in Mtwapa creek on the Kenyan coast was studied. Both the qualitative and quantitative spectra of the diets of these fish species were investigated. It was found that the eight most abundant fish species, Sardinella gibbosa, Pellona ditchella, Spratelloides delicatilus, Atherinomorous lacunosus, Gerres oyena, Secutor insidiator and Leiognathus equula , consumed principally copepods, while Selar crumenophthalmus fed mainly on fish scales. Polychaetes were an important diet for Gerres oyena and Leiognathus equula . Spratelloides delicatilus was a carnivore feeding only on zooplankton and zoobenthos, and had the lowest diet diversity (H' = 0.40). The rest were omnivorous. Sardinella gibbosa, P. ditchella, L. equula, Sec. insidiator, G. oyena and Sel. crumenophthalmus fed on phytoplankton, zooplankton, zoobenthos and detritus with a relatively higher diet diversity (H' = 0.68–0.96). Atherinomorous lacunosus did not take detritus in its diet and it had a lower diet diversity compared to the other omnivores (H' = 0.47). The feeding niches of the examined species were highly overlapped. The Morisita feeding niche overlap values ranged between 0.84 and 1.00. Most of them were generalized opportunistic feeders except for S. dilicatilus, which exhibited a specialised feeding strategy. Overall, this study showed that the fishes had a flexible diet, which relied greatly on the prevailing biotic and abiotic conditions in their habitats. Keywords : trophic ecology, fish, Mtwapa, Kenya West Indian Ocean Journal of Marine Science Vol. 3 (2) 2004: pp. 179-188

A review of the Gerres subfasciatus complex from the Indo-West Pacific, with three new species (Perciformes: Gerreidae)

Gerres japonicus Bleeker, 1854, and Gerres subfasciatus Cuvier in Cuvier and Valenciennes, 1830, are redescribed, and Gerres akazakii sp. nov. (Japanese endemic), Gerres ryukyuensis sp. nov. (Okinawa I., Japan), and Gerres shima sp. nov. (Indo-Malayan region, including the Andaman Sea, Southeast Asia, southern China and Taiwan, and Ryukyu Is., Japan) are described. Gerres ovatus Gunther, 1859, and Gerres kapas Bleeker, 1854, are recognized as junior synonyms of G. subfasciatus and Gerres oyena (Forsskal, 1775), respectively. All species (except G. oyena) have a small (<170 mm in standard length: SL), moderately deep (depth 36–48% SL), body with dark vertical bars, dorsal fin rays X, 9 or IX, 10, and 31/2 or 41/2 scale rows between the 5th dorsal fin spine base and lateral line, defined as the G. subfasciatus complex. The five species can be variously differentiated from each other by dorsal head squamation, and differing meristic, morphometric, and color characters. They are generally distributed sympatrically in the Indo-West Pacific. Other nominal species of uncertain status or relationship are discussed.

Community structure and temporal variability of juvenile fish assemblages in natural and replanted mangroves, Sonneratia alba Sm., of Gazi Bay, Kenya

The juvenile fish community associated with natural, degraded and replanted Sonneratia alba mangroves in Gazi Bay was sampled during the South East and North East monsoons between April 2002 and June 2003. A total of 1800 individuals belonging to 49 taxa and 34 families were collected from the intertidal forest using stake nets. Fish abundance ranged from 0.93 ± 0.20 ind. m −2 (SEM02) to 1.16 ± 0.18 ind. m −2 (SEM03) between seasons and between 0.54 ± 0.07 ind. m −2 and 1.64 ± 0.33 ind. m −2 for individual sites across seasons. Five taxa accounted for approximately 70% of the total fish abundance, with Gobidae and Gerres oyena dominating. ANOSIM revealed seasonal differences in fish species composition and abundance ( p = 0.01) due to fluctuating abundances of primarily Terapon sp. and Thryssa sp. The majority (65%) of fishes were reef associates, which implies a tight coupling between mangroves and coral reefs. The high proportion (75%) of commercial species indicates that fringing S. alba mangroves of Gazi Bay are important in sustaining coastal fisheries in the area. The fact that the replanted mangroves of Gazi Bay harbor a significant number of commercially important species as juveniles suggest their function as nursery habitats for nekton may well have been restored. This study is original in quantitatively evaluating the use of replanted intertidal mangroves by juvenile fish in the West Indian Ocean; a topic poorly studied worldwide to date.

Spatial and temporal variation in fish community structure of a marine embayment in Zanzibar, Tanzania

Spatial and temporal variation in the fish community structure were studied in a tropical non-estuarine embayment in Chwaka Bay, Zanzibar (Tanzania). Fish samples were collected bi-monthly (at each spring low tide) for 1 year (November 2001–October 2002) from a range of bay habitats ranging from mangroves deep inside the bay to seagrass beds close to the mouth of the bay. Additionally, environmental variables were examined to determine their relationship with the fish community structure. Being a non-estuarine embayment, the environmental variables as well as the fish community structure in each habitat remained relatively constant for most part of the year; however, a marked decline was observed during the rainy period (April–May). Significant variations in fish community variables (density, biomass and species richness) and in water temperature and salinity were observed during the rainy season in all habitats, with larger changes in the mangrove and mud/sand flats habitats than in the seagrass beds. Seasonal variations in water clarity and dissolved oxygen were not significant, though. Many species disappeared from the mangrove and mud/sand flats habitats during the rainy season and those which persisted showed a remarkable decrease in density. Moreover, the results indicate that mangroves were the preferred settling habitats for Gerres filamentosus, Gerres oyena, Lethrinus lentjan and Monodactylus argenteus, especially during the dry period (December–February) before the rainy season. This observation is contrary to what has been reported from some other tropical regions where greater abundance and species richness was observed during the rainy season. A significant relationship was found between density of fish and temperature, salinity and turbidity. Since salinity was the most conspicuously changing environmental variable with seasons, we propose that salinity, alone or in combination with low visibility and temperature, was probably the most important environmental factor structuring the fish assemblage in the mangrove and mud/sand flats habitats, particularly during the rainy season.

Light and electron microscopy of Paranella diplodae N. SP. (Polyopisthocotylea;Microcotylidae; Monogenea ) from some Red Sea Teleost fishes in Egypt

The present study deals with a monogenean parasite infecting, some marine fish through light and scan electron microscopy. It revealed that the percentage of infection was 48% (14 out of 50 fish), 28% (14 out of 50 fish), 22% (11 out of 50 fish) and 16% (8 out of 50 fish) in Diplodus noct, Gerres oyena, Lethrinus elongates and Siganus revulatus, respectively. The present work recorded Paranaella diplodae (Polyopisthocotylea; Microcotylidae; Monogenea) as a new species collected from the investigated fish gills. They are lanculate flukes, the haptor is not distinguished from the body proper approximately 1/3 of the whole body length. The surface topography of the parasite bears small pits and conspicuous transverse folds and richly supplied with papillae-like unicellate sensory ending. The opisthohaptor is typical of Microcotylidae. The clamp structure and the haptoral tegument are similar to the rest of the body

The importance of mangroves, mud and sand flats, and seagrass beds as feeding areas for juvenile fishes in Chwaka Bay, Zanzibar: gut content and stable isotope analyses

The relative importance of bay habitats, consisting of mangrove creeks and channel, seagrass beds, and mud and sand flats, as feeding grounds for a number of fish species was studied in Chwaka Bay, Zanzibar, Tanzania, using gut content analysis and stable isotope analysis of carbon and nitrogen. Gut content analysis revealed that within fish species almost the same food items were consumed regardless of the different habitats in which they were caught. Crustaceans (mainly copepods, crabs and shrimps) were the preferred food for most zoobenthivores and omnivores, while fishes and algae were the preferred food for piscivores and herbivores, respectively. The mean δ13C values of fishes and food items from the mangrove habitats were significantly depleted to those from the seagrass habitats by 6·9 and 9·7‰ for fishes and food items, respectively, and to those from the mud and sand flats by 3·5 and 5·8‰, respectively. Fishes and food items from the mud and sand flats were significantly depleted as compared to those of the seagrass habitats by 3·4 and 3·9‰, for fishes and food, respectively. Similar to other studies done in different geographical locations, the importance of mangrove and seagrass themselves as a primary source of carbon to higher trophic levels is limited. The different bay habitats were all used as feeding grounds by different fish species. Individuals of the species Gerres filamentosus, Gerres oyena, Lethrinus lentjan, Lutjanus fulviflamma, Pelates quadrilineatus and Siganus sutor appeared to show a connectivity with respect to feeding between different habitats by having δ13C values which were in‐between those of food items from two neighbouring habitats. This connectivity could be a result of either daily tidal migrations or recent ontogenetic migration.