[en] Measuring high-energy to very high energy (VHE) gamma-rays is now a completely mature technique and hundreds of sources have already been identified. However, the gamma-rays can be originated from either leptonic or hadronic mechanisms. Only very detailed studies of the spatial profile of the sources and on the shape of the high-energy spectrum can be used to hint the hadronic emission. This requires a large statistic which is quite difficult to obtain at VHE. On the contrary, high-energy neutrinos are a unique signature of these hadronic processes. Neutrinos present the advantage to point directly to their sources (neutral particle). However, neutrinos are incredibly difficult to detect, 1/10000000 neutrinos interact in or close to the detector. It requires gigantic detection volumes, probably larger than 1 km³. The context of the time-domain astronomy and the multi-messenger analysis is described in Chapter 2. My works in this field was from the beginning to look for these neutrino sources with the maximal sensitivity possible, concentrating on the detection of transient sources. By design, neutrino telescopes constantly monitor at least one complete hemisphere of the sky and are thus well suited to detect neutrinos produced in transient astrophysical sources. The flux of high-energy neutrinos from transient sources is in general lower than the one expected from steady sources. But, the background originating from atmospheric neutrinos can be drastically reduced by requiring a directional and temporal coincidence with the direction and time of the astrophysical phenomena detected by a satellite or a telescope. For a typical duration of a flare (1-100 days), we can gain at least a factor ∼2-3 in the discovery potential compared to a steady point-like source analysis. We have applied this time-dependent analysis to different catalogues of blazars, X-ray binaries, gamma ray bursts and fast-radio bursts. The results of these searches are summarized in Chapter 3. Pushing this method at the maximum, i.e. detecting one source with only one neutrino, is at the basis of the TAToO project, started mid 2008. It consists of the online follow-up by external telescopes of a selected sample of 'potential' cosmic neutrinos. The results of these searches with ANTARES are summarized in Chapter 4. Recently, we have upgraded the online analysis platform to be able to process in real-time any potential electromagnetic transient triggers and multimessenger alerts. We have been following all gamma-ray burst triggers detected by Fermi and Swift, the IceCube high-energy neutrino alerts, the LIGO/VIRGO gravitational waves candidates and other transients. The results of these online follow-ups are presented in Chapter 5. ANTARES is already running smoothly since 2007 without major interruption. Even if its detector size is quite small (1/100 of a cubic kilometer), we have performed a lot of multi-messenger analyses, plenty of them with competitive results than IceCube. Since a few years, we are building the second generation neutrino telescope in the Mediterranean Sea, which consists of two detectors: the low-energy site, ORCA, in France and the high-energy one, ARCA, in Italy. In this manuscript, I will only concentrate on the physics potential related to astronomy. What I like about this kind of detector is that there are a very versatile scientific case with the same data in particle physics (neutrino oscillation, standard model physics), astronomy or marine sciences. The KM3NeT detector is described in Chapter 6. In KM3NeT, we have started the implementation of the real-time analysis framework that would allow to pursue the real-time multi-messenger analyses started in ANTARES with the upgraded detector sensitivities and improved analysis methods. In 2015, I have also joined the SVOM Collaboration to go further on the analysis of the extreme sources in the Universe, in particular the detailed studies of the gamma-ray bursts. It will also permit to secure the link between KM3NeT and SVOM, providing simultaneous X-ray/γ-ray observations to the neutrino emission, so important for the understanding of the micro-physics of the jets. In this project, I am working on the ground segment of SVOM, mainly on the COLIBRI telescope, one of the SVOM ground facilities. On this telescope, I am working on the analysis software and on the link between the different ground and space instruments. SVOM activities are described in Chapter 7. Finally, a conclusion and some perspectives are given in Chapter 8