PERFORMA REPRODUKSI DAN LARVA IKAN GABUS (Channa striata Blkr) DENGAN BEBERAPA TEKNIK PEMIJAHAN

Sejumlah penelitian terhadap ikan gabus (Channa striata Blkr) telah dilakukan mulai dari pembenihan dan pembesaran, namun masih belum banyak informasi ilmiah terkait performa reproduksi dan larva yang dihasilkan baik dari pemijahan alami maupun pemijahan semi-alami (induksi hormonal). Penelitian ini bertujuan untuk menentukan teknik pemijahan yang tepat untuk ikan gabus. Dalam penelitian ini digunakan induk jantan dan betina dengan tingkat kematangan gonad (TKG) yang seragam (yaitu pada TKG-IV). Penelitian memakai empat perlakuan stimulasi hormon, yaitu A (kontrol, tanpa stimulasi hormon), B (induk jantan dan betina distimulasi hormon), C (induk betina distimulasi hormon), D (induk jantan distimulasi hormon). Hormon yang digunakan untuk menginduksi induk betina dan jantan adalah LHRHa + anti dopamin. Masing-masing perlakuan menggunakan tiga pasang induk. Parameter performa reproduksi yang diamati meliputi fekunditas, diameter telur, lama waktu menetas, dan volume kuning telur. Untuk performa larva dilakukan pengamatan laju penyerapan kuning telur, pertumbuhan panjang dan bobot larva, laju pertumbuhan spesifik, dan sintasan. Dari penelitian diperoleh bahwa ikan perlakuan-A dan B mampu berovulasi hingga menetas, perlakuan-C berhasil ovulasi namun gagal menetas, sedangkan perlakuan-D tidak mampu ovulasi. Fekunditas dan derajat penetasan hasil pemijahan alami paling tinggi (1.832 ± 13 butir dan 97,20 ± 2,49%). Namun, waktu ovulasi dan waktu menetas pemijahan alami (159,50 ± 0,50 jam dan 3.210,00 ± 5,00 menit) lebih lama dibanding pemijahan buatan (26,00 ± 2,00 jam dan 2.370.00 ± 15,00 menit). Abnormalitas terjadi pada perlakuan-B (1,30 ± 0,42%), sedangkan larva hasil perlakuan-A tidak ada yang abnormal. Berdasarkan hasil penelitian ini selain pemijahan alami, ikan gabus dapat dipijahkan secara buatan melalui stimulasi hormon pada induk jantan dan betina.Various studies on snakehead fish (Channa striata Blkr) have been carried out from breeding, nursery, to grow-out. Nevertheless, information regarding reproductive performance and produced larvae either from natural spawning or semi-natural (hormonal induction) spawning are still limited in the literature. This study aimed to determine the appropriate spawning technique for snakehead fish. In this study, the fish males and females were used with a uniform gonad maturity level. The study used four hormone stimulation treatments, namely: A (control, without hormone stimulation), B (male and female parents were hormone-stimulated), C (hormone-stimulated female parent), D (hormone-stimulated male parent). The hormone used to induce female and male broodstock was LHRHa + anti-dopamine. Each treatment used three pairs of parents. Parameters of reproductive performance observed included fecundity, egg diameter, hatching time, and egg yolk volume. For larval performance, observations were made of the rate of egg yolk absorption, growth in length and weight of larvae, specific growth rate, and survival. The research found that fish in treatment-A and B were able to ovulate, and the produced eggs could hatch. Fish in treatment-C managed to ovulate but failed to hatch, while treatment-D could not ovulate. The fecundity and hatching rates of the natural spawning were the highest (1,832 ± 13 grains and 97.20 ± 2.49%). However, the time of ovulation and hatching time for natural spawning (159.50 ± 0.50 hours and 3,210.00 ± 5.00 minutes) were longer than those of artificial spawners (26.00 ± 2.00 hours and 2,370.00 ± 15.00 minutes). Abnormalities occurred in treatment-B (1.30 ± 0.42%), while the larvae from treatment-A were normal. Based on the results of this study, in addition to natural spawning, snakehead fish can be spawned artificially through hormonal stimulation of male and female broodstock.

Multiple Lines of Evidence Indicate Limited Natural Recruitment of Golden Perch (Macquaria ambigua) in the Highly Regulated Lachlan River

Freshwater ecosystems and their associated biota have been negatively impacted by the human development of water resources. Fundamental to restoration activities for target species is an understanding of the factors affecting population decline or recovery. Within Australia’s Murray–Darling Basin, recovery efforts to address the population decline of native freshwater fish include stock enhancement, habitat restoration, and the delivery of environmental water. Essential to guiding future management actions is information to assess the efficacy of these efforts. We undertook a study to investigate whether natural spawning and recruitment, stock enhancement, or a combination of the two is contributing to sustaining populations of golden perch (Macquaria ambigua) in the highly regulated Lachlan River, Australia. Otolith microchemistry and genetic analyses were used as complementary tools to determine the source (hatchery origin or wild-spawned) of existing populations in the catchment. We identified that natural spawning and recruitment was contributing to riverine populations in some years but that populations were heavily reliant on stocking. It was not possible to distinguish hatchery and wild-born fish using genetic tools, highlighting the value of using multiple lines of evidence to establish causal mechanisms contributing to population recovery.

ESTIMATION OF ABUNDANCE FOR THE MIGRATING JUVENILE PINK SALMON IN THE RIVERS OF SAKHALIN AND ITURUP ISLANDS IN 2019

Number of the pink salmon fry migrating downstream from their spawning grounds in the control rivers in 2019 is assessed as 17546.2 . 103 and 14795.7 . 103 ind. for the Dagi and Bolshoi Khuzi Rivers (northeastern Sakhalin), as 89.1 . 103 and 2636.1 . 103 ind. for the Poronai River tributaries — the Kholodny and Orlovka, as 2759.8 . 103 and 21456.0 . 103 ind. for the Lazovaya and Pugachevka Rivers (western coast of the Patience/Terpeniya Bay), as 5803.8 . 103 and 19020.0 . 103 ind. for the Voznesenka and Ochepuha Rivers (southeastern Sakhalin), as 1822.4 . 103 and 2139.0 . 103 for the Taranai and Kura Rivers (Aniva Bay coast), and as 15834.1 . 103 and 7626.1 . 103 ind. for the Rybatskaya and Olya Rivers (Iturup Island), respectively. In all areas, the pink juveniles migrated from the spawning grounds earlier than usual, obviously because of accelerated development of the embryos in conditions of abnormally warm autumn. The number of juveniles migrated from all spawning grounds in the rivers of respective regions is estimated taking into account the escapement of pink salmon spawners and the downstream migration index determined for the control rivers (ratio of the spawners escapement and the number of subsequent downstream migrating juveniles): the total number for the natural spawning grounds is estimated as 1168.9 . 106 ind. for the rivers of the eastern coast of Sakhalin (including the Aniva Bay) and 471.1 . 106 ind. for the rivers of Iturup Island (Okhotsk Sea coast). Additional 141.3 . 106 ind. were released from artificial hatcheries of eastern Sakhalin and 122.0 . 106 ind. — from artificial hatcheries of Iturup Island. The downstream migration is considered as highly abundant for northeastern Sakhalin and Iturup Island, but is insufficiently abundant for the Patience/Terpeniya Bay and Aniva Bay where the landings of this generation should be limited. The pink salmon return to southeastern Sakhalin in 2020 is expected to be better than in 2018 due to satisfactory abundance of the juveniles from natural spawning grounds.