It is extensively recognized that seagrass meadows have been defined as nursery ground for fish. In this study, we investigated species composition and abundance of small fishes in seagrass beds of Karang Congkak Island, Kepulauan Seribu National Park from November 2018 to March 2019. In total, about 10,000 individuals of 46 fish species belonging to 26 families were captured using a seine net at four fix stations. The major families graded by species number were Labridae, Apogonidae, Gobiidae, Siganidae, and Atherinidae. More than 90% of fish was juvenile and mostly economically important species and reef-associated fish. Majority of fish juveniles inhabit seagrass beds were categorized as temporary resident and regular visitors. It was observed that the top five ranked fish species in abundance were Spratelloides gracilis (33.4%), Stenatherina panatela (19.5%), Siganus canaliculatus (13.2%), Gerres oyena (11.8%) and Siganus spinus (5.9%). There was a propensity that species richness and diversity were higher in areas with higher seagrass coverage. However, two-way ANOSIM revealed fish abundance was not significantly different spatially and temporally (p>0.05). Predominant trophic function of fish were zooplanktivores and crustacivores. The present study, therefore, identified seagrass beds of Karang Congkak Island as feeding habitats and shelter for fish juveniles.

A seagrass bed of Karang Congkak Island has been known as the nursery habitat for many marine fishes. The common silver-biddy (Gerres oyena) is one of the temporary resident fishes that inhabits seagrass beds of Karang Congkak Island before they migrate to their adult habitat to join the adult population. The aims of this research are to analyze the growth pattern, condition factor and food preferences of the common silver-biddy while they utilized the seagrass beds of Karang Congkak Island as their nursery ground. Sampling was conducted from March 2018 to March 2019 with 10 times frequency of sampling in total. Sample was towed using a beach seine net with 10x1 m in dimension and 3 mm mesh size.  Parameters that were analyzed in this research were a length-weight relationship, condition factor, and food preferences. A total of 2762 juveniles of the common silver-biddy were collected and were classified into 10 length classes. The results showed that in general, the growth pattern of the common silver-biddy was positive allometric (b>3), although some months were isometric (b=3). The overall condition factor ranged from 0.87 – 2,05 and it fluctuated throughout the months. The diet which has the main role in determining the fish growth of the common silver-biddy was dominated by the group of copepods. The positive allometric growth pattern of the common silver-biddy and the high value of condition factor describe that seagrass ecosystem of Karang Congkak Island is a suitable nursery ground for the juveniles of the common silver-biddy. Abstrak Ekosistem lamun Pulau Karang Congkak merupakan habitat pengasuhan yuwana berbagai spesies ikan laut. Ikan kapas-kapas (Gerres oyena) merupakan salah satu ikan penghuni sementara lamun Pulau Karang Congkak sebelum akhirnya beruaya ke habitat induknya untuk bergabung dengan populasi ikan dewasa. Penelitian ini bertujuan untuk menganalisis pola pertumbuhan dan faktor kondisi yuwana ikan kapas-kapas selama menghuni perairan ekosistem lamun Pulau Karang Congkak. Penelitian dilakukan dari Maret 2018 sampai Maret 2019 dengan total frekuensi pengambilan sampel selama 10 bulan. Contoh ikan diambil dengan menarik pukat tarik pantai berdimensi 10 m x1 m dan mata jaring 3 mm. Parameter yang diamati pada penelitian ini adalah hubungan panjang-bobot ikan, faktor kondisi, dan preferensi makanan ikan. Selama penelitian terkumpul sebanyak 2765 yuwana ikan yang dapat dikelompokkan menjadi 10 kelompok kelas ukuran panjang. Pola pertumbuhan panjang ikan kapas-kapassecara keseluruhan bertipe alometrik positif (b > 3), namun pada beberapa bulan tertentu ditemukan pola pertumbuhan isometrik (b=3). Faktor kondisi selama penelitian berkisar antara 0,87-2,05 dan berfluktuasi setiap bulan. Makanan ikan yang merupakan faktor penentu pertumbuhan ikan kapas-kapas didominasi oleh kelompok kopepoda. Pola pertumbuhan ikan kapas-kapas yang alometrik positif dengan faktor kondisi yang tinggi memberikan gambaran bahwa padang lamun Pulau Karang Congkak merupakan daerah asuhan yang baik bagi yuwana ikan kapas-kapas.

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.

Diet and feeding ecology studies are a principal tool to understand the functional role of fish within their habitat. Like most coastal habitats, seagrass meadow provides food and refuge for many biotas. Karang Congkak Island is a small uninhabited island situated in the northern part of the Kepulauan Seribu National Park and surrounded by a seagrass ecosystem. The current study aims to analyze diet composition changes and trophic attributes of the common silver-biddy, Gerres oyena, in the seagrass ecosystem of the Karang Congkak Island. The research was carried out monthly from March to September 2018 by towing the beach seine net. Data analysis includes diet composition, niche breadth, and feeding strategy. During the study period, 1,196 individuals of G. oyena were captured, and most of them were juveniles. Fifty-nine types of prey were documented and arranged into six groups, namely phytoplankton, algae, zooplankton, zoobenthos, crustaceans, and unidentified material. G. oyena shows an ontogenetic change, from zooplanktivore to crustacivore and zoobenthivore. Moreover, this species has a TROPH value ranging from 3.00-3.31 and is categorized as omnivorous that tend to feed on animals. The interpretation of prey-specific abundance and niche breadth confirms that this species developed specialized and generalized feeding strategies.

Ikan Jaguar, Parachromis managuensis merupakan ikan asing dari Famili Cichlidae yang berpotensi menjadi ikan invasif dan mengancam terjadinya penurunan sumberdaya ikan asli dan endemik di perairan Waduk Penjalin, Brebes, Jawa Tengah. Tujuan dari penelitian ini adalah untuk mengidentifikasi ikan P. managuensis berdasarkan karakter morfometrik dan meristiknya. Pada penelitian ini sebanyak 50 individu ikan P. managunesis dikumpulkan dari nelayan di Waduk Penjalin pada bulan November 2022 dan dianalisis 20 karakter morfometrik dan tujuh karakter meristiknya. Sebanyak 21 ikan berada pada stadia yuwana dan 29 adalah ikan dewasa yang dapat dikelompokkan mejadi tujuh kelas ukuran panjang. One-Way Anova, Analisis Kluster, Principal Component Analysis digunakan untuk menganalisis karakter morfometrik sedangkan uji Kruskal-Wallis digunakan untuk  mengetahui adanya perbedaan karakter meristik berdasarkan kelas ukuran panjang. Hasil dari pengujian One-way Anova menunjukkan sebanyak 15 karakter morfometrik berbeda secara signifikan. Ikan pada kelas ukuran kecil (yuwana) dan besar (dewasa) dapat dibedakan berdasarkan  karakter morfologi di bagian kepala yakni PoL (Panjang Postorbital), SnL (Panjang Moncong), HL (Panjang Kepala), dan PreDL (Panjang Sebelum Sirip Dorsal). Akan tetapi, karakter meristik menunjukkan tidak adanya perbedaan berdasarkan kelas ukuran panjang ikan.