Macrobrachium. spp atau biasa disebut dengan udang galah memiliki nilai harga ekonomis yang tinggi dibandingkan dengan jenis udang tawar lainnya. keberadaan spesies ini menjadi sesuatu yang harus dipertahankan sehingga upaya konservasi terhadap lingkungan biologi menjadi faktor penting. tujuan penelitian ini untuk mengetahui komposisi ukuran dan hubungan panjang berat udang galah (macrobrachium. spp) yang tertangkap oleh alat tangkap bubu di sungai kayan kabupaten bulungan. metode penelitian secara deskriptif kualitatif dan kuantitatif dengan pendekatan survei dan observasi. metode pengambilan sampel berdasarkan purposive sampling dilakukan di sungai kayan dan pos penjualan udang galah daerah tanjung palas selama 2 bulan (februari – maret 2023) dengan total sampel sebanyak 360 ekor. pengamatan dan pengukuran sampel menghasilkan data berupa panjang total (pt), berat (b), panjang karapas (pkr), dan panjang abdomen (pab). hasil analisa data komposisi ukuran diketahui terbentuk 9 kelas dengan kisaran kelas, ukuran panjang total 8,4 – 26,3 cm, panjang karapas 2,9 – 10,0 cm, panjang abdomen 5,4 – 14,3 dan komposisi berat 25,4 – 254,8 gram. pertumbuhan udang galah sampel total, jantan dan betina bersifat allometrik positif. sifat pertumbuhan pada udang galah jantan maupun betina yaitu pertambahan berat lebih cepat dibandingkan dengan panjang atau ekspresi bentuk tubuh udang galah selama penelitian cenderung gemuk atau montok. kata kunci: komposisi ukuran, hubungan panjang berat, udang galah, bubu, sungai kayan

Giant prawns, also known as macrobrachium spp., are more expensive economically than other varieties of freshwater prawns. because it is necessary to preserve this species' survival, the biological environment's conservation plays a significant role. in this study, the length-weight relationships and size distribution of giant prawns (macrobrachium spp.) collected using bubu (trap fishing equipment) in the kayan river, bulungan regency, were examined. a survey and an observational methodology were used in the descriptive, qualitative, and quantitative research method. the giant prawn sales post at tanjung palas and the kayan river were sampled using the purposive sampling technique over the course of two months (february-march 2023) using a total sample of 360 people. data on the sample's total length (pt), weight (b), carapace length (pkr), and abdominal length (pab) were obtained through observation and measurement. the result of the analysis of the size composition data, there were nine classes with a range of classes, a total length between 8.4 and 26.3 cm, a carapace length between 2.9 and 10.0 cm, an abdominal length between 5.4 and 14.3 cm, and a weight range between 25.4 and 254.8 grams. the overall, male, and female samples of gigantic prawns all showed positive allometric growth. both male and female giant prawns grew in such a way that weight gain outpaces either length gain or expression of body shape, which during the study tended to be fat or plump. keywords: size composition, length-weight relationships, giant prawn, bubu, kayan river