Population structure of tropical eel (Anguilla bicolor bicolor) in Cikaso River, West Java

A. bicolor bicolor is a tropical eel subspecies that dominate catches in the coastal areas of West Java, and its conservation status is near threatened. Cikaso River, West Java, becomes eel migration path, while unfortunately, information concerning the stock of eel in this river is still inadequate. The objective of this study was to determine the population structure (size distribution, length-weight relationship, and condition factor) of A. bicolor bicolor in the Cikaso River. The research was carried out in the main streams of the Cikaso River and the coastal marsh of Ciroyom from January to December 2020. Eel samples were collected using lift-net, fishhook, and traps. The number of eels caught is counted, then the total length and weight are measured. We collected nine elvers and 89 yellow eels, but no silver eel was caught during the study. The elver's total length (TL) ranged from 10.2 to 20 cm, and the TL of yellow eel ranged from 20.1 to 42.2 cm. The catch of eel is dominated by the size of 25-30 cm. The growth pattern of eel in the Cikaso River is positive allometric, with the condition factor of eel ranging from 0.450 to 1.917 (1.160±0.3096).

Masculinization of Tropical Eel Anguilla bicolor McClelland in Different Population Density

In general, female eel dominates the results of catching eel in the river. Male fish dare rarely found in nature, therefore masculinization is necessary for obtaining in males. The administration of 17α-methyltestosterone to masculinize Anguilla bicolor McClelland. It is a synthetic anabolic-androgenic steroid which has potential to endocrine disrupter that disturbed function of normal reproduction in human or animal. It urgently needed that a masculinization technique needs to study the use of an environmental factor. Population density is one of the environmental factors that influence gender determination (ESD-environmental dependent sex determination). This will result in increased cortisol secretion, which will further stimulate the synthesis of 11-KT steroids that affect male gonad differentiation. This study aims to induce masculinization in tropical eel Anguilla bicolor McClelland in different density. Three treatments and three replicates conducted the research. The treatments were one fish.48 L-1, two fish.48 L-1 and three fish.48 L-1. Eels size was approximately similar, at 16,78 g±0,62 in weight, and 25,38 cm±0,15 in length were either culture in brackish water for eight weeks. The results showed that density population treatment significantly increased the Fin Index (P<0.05), but no sign for Eye Index, GSI, HSI, and testosterone level. The highest male population (77,8%) achieves at the highest density treatment, three fish.48 L-1 population density. It can be concluded, based on reproductive observations, population density does not affect gonad maturity/puberty, but the high population density (3 fish.48 L-1)stimulates Anguilla bicolor McClelland masculinization.

Species composition of glass eels (Anguilla spp.) recruiting to the Palu River, Central Sulawesi

Demand for tropical eel seed has been increased and many tropical eel populations are under pressure. To conserve eel biodiversity and manage eel populations sustainably, it is necessary to identify eel species and their recruitment patterns at regional and watershed scales. The research objective was to determine the species composition and temporal recruit-ment patterns of glass eels recruiting to Palu River in Central Sulawesi. Glass eels sampling were conducted in January-April 2009, May-November 2010 and April-December 2011. Identification under anaesthetic (15-17.5 ppm clove oil solution) was based mainly on the number of ano-dorsal vertebrae (ADV). Species composition was dominated by two commercially species, Anguilla marmorata and A. bicolor pacifica with substantial variation and no clear temporal patterns. Specimens of other species that important from conservation and biodiversity aspects were present at each month but cannot be accurately identified using the ADV method. DNA analysis method is required to identify these specimens.

Effectively Of 17α-Methyltestosterone on Tropical Eel, Anguilla bicolor McClelland Masculinization in Different Salinity Culture

Eel population in nature reaches critical number, so that culture strategy is urgently needed to fulfil the high demand of this fish. A shortcut to get functional male, which proven difficult to be founded from natural catching, is masculinization. This research aimed to induce masculinization of tropical eel, Anguilla bicolor McClelland supplemented with various doses of 17α-methyltestosterone during a month culture in freshwater (0 ppt) or brackish water (10 ppt). The eel was grouped and fed with supplementation of 17α-methyltestosterone at various doses, depending upon treatments, namely 0 mg Kg-1 diet (control), 40, 80 or 120 mg Kg-1 diet. Eels size were similar, at approximately 16,78 g ± 0,62 in weight and 25,38 cm ± 0,15 in length were either culture in freshwater or brackish during the experiment for eight weeks. Sex gonad, based on anatomical histological structures, Eye Index and Fin Index were measured after time culture treatment achieved, as well as body length, weight, eye diameter and the length of the pectoral fin were measured. Results showed that supplementation 17α-methyltestosterone 80 mg/Kg diet culture in brackish water has the highest number of male (90%). This study proven that, the hormone was effective for masculinization in eels, It useful for masculinization in eels. Results proved that the 17α-methyltestosterone highly significant (P<0.01) effect on the Eye index (3.63 – 5.14) and Fin Index (3.03 – 4.08) of eels. This study concluded, that 17α-methyltestosterone more effective in improving the number of males in brackish water than in freshwater culture.

Karakteristik reproduksi ikan sidat Anguilla bicolor McClelland, 1844 yang diinduksi GNRH-analog

Eel, Anguilla bicolor McClelland was hard to mature in captivity, due to low levels of pituitary gonadotropin. In order to stimulate gonadal maturation in captivity, exogenous gonadotropin is needed. The purpose of this study was to assess the effect of GnRH-analog induction on gonadal maturation of tropical eel base on the value of the eye index, gonado-somatic index, and estradiol levels. The study was carried out experimentally with a completely randomized design with three treatments and eight replications. The treatments were the induction of hormone GnRH-analogues with doses of 0.0; 0.5 and 1.0 ml kg-1 body weight. Eel with an average total length of 67 cm and an average weight of 500 g were injected with different doses of GnRH-analog (0.0; 0.5 and 1.0 ml kg-1 body weight), kept in the fiberglass aquarium for two months. The eels were fed with discard fish daily in ad libitum at 16.00 pm. The observed variables were eye index, Gonadosomatic Index (GSI), and estradiol levels. The results showed that injection of three different doses of GnRH-analog did not affect on the increasing of GSI, eye index (P> 0.05), and estradiol (P <0.05). Induction of GnRH-analog of 0.0; 0.5 and 1.0 ml kg-1 body weight can not stimulate the gonadal maturity of tropical eel. AbstrakIkan sidat Anguilla bicolor McClelland sulit matang gonad dalam kondisi budi daya, karena rendahnya kadar gonado-tropin pituitari. Oleh karena itu untuk memacu pematangan gonad ikan sidat dalam kondisi budi daya perlu ditambah-kan gonadotropin secara eksogen. Tujuan penelitian ini adalah mengkaji pengaruh induksi GnRH-analog terhadap pe-matangan gonad ikan sidat berdasarkan perubahan nilai indeks mata, indeks kematangan gonad (IKG), dan kadar estradiol. Penelitian dilakukan secara eksperimental menggunakan rancangan acak lengkap dengan tiga perlakuan dan delapan ulangan. Perlakuan percobaan terdiri atas induksi hormon GnRH-analog dengan dosis 0,0; 0,5 dan 1,0 ml kg-1 bobot badan. Ikan sidat dengan rata-rata ukuran panjang 67 cm dan rata-rata bobot 500 g sebanyak 18 ekor yang telah diinduksi dengan berbagai dosis GnRH analog (0, 0,5 dan 1 ml kg-1 bobot badan) dipelihara dalam akuarium fiberglass selama dua bulan. Pakan berupa ikan rucah diberikan satu kali sehari pada pukul 16.00 secara ad libitum. Variabel yang diamati adalah indeks mata, IKG, dan kadar estradiol. Hasil penelitian menunjukkan bahwa induksi hormon GnRH-analog tidak berpengaruh terhadap peningkatan nilai indeks mata, nilai IKG (p>0,05), dan kadar estradiol ikan sidat (p<0,05). Induksi hormon GnRH-analog dengan dosis 0,5 dan 1 ml kg-1 bobot badan tidak efektif memacu pematangan gonad ikan sidat.

Tropical Eel: Vulnerability Approach untuk Pengelolaan Berkelanjutan

Sumberdaya ikan sidat di Cimandiri memiliki interaksi kuat dengan perairan Samudra Hindia. Penangkapan dilakukan terus-menerus, baik larva maupun dewasa dikhawatirkan berisiko terhadap keberlanjutan stok. Praktik pemanfaatan dan pengelolaan yang dilakukan tidak sepenuhnya memperhatikan kaidah keberlanjutan ilmiah yang memadai. Untuk itu, penelitian ini dilakukan dengan mengkaji mengenai sustainability dan productivity sebagai basis data kerentanan dilakukan selama Juli–Oktober 2013 pada 5 titik pengamatan sepanjang sungai Cimandiri. Analisis indek komposit dengan pendekatan jarak dengan indek Jaccard. Hasil kajian keretanan ikan sidat berkisar antara 1,31–1,66. Nilai tersebut menunujukkan bahwa potensi keberlanjutan tinggi dan kerentanan rendah dengan menggunakan klasifikasi NOAA (2009). Stok dengan indek di bawah 1,8 tergolong kurang rentan dan potensi keberlanjutan masih baik.