A microfluidic device configured for observation of fish larva of zebrafish, medaka (Oryzias latipes), antarctic fish (suborder Notothenioidei), Mexican tetras (Astyanax mexicanus), toadfish (Batrachoididae), bicolor damselfish (Stegastes partitus) or platyfish (Xiphophorus maculatus), the microfluidic device comprising: an incubation layer , the incubation layer including: at least one dock , each of the at least one dock defines a stepped tank comprising an upper tank and a lower tank , an inflow channel in fluid communication with the stepped tank for supplying a fluid to the stepped tank , and an outflow channel in fluid communication with the stepped tank for draining the fluid from the stepped tank , wherein the upper tank is larger than the lower tank to allow culturing of the fish larva therein, and wherein the geometry of the lower tank fits the dimension of the fish larva to reversibly receive the fish larva from the upper tank and to dock the fish larva at a controlled orientation for imaging or observation, wherein the microfluidic device further comprising: a loading layer removably attached to the incubation layer , the loading layer including: at least one stepped well , each of the at least one stepped well comprising an upper well and a lower well , each of the at least one stepped well in fluid communication with a respective dock , wherein the geometry of the upper well is configured to accommodate a single fish embryo of the zebrafish, medaka (Oryzias latipes), antarctic fish (suborder Notothenioidei), Mexican tetras (Astyanax mexicanus), toadfish (Batrachoididae), bicolor damselfish (Stegastes partitus) or platyfish (Xiphophorus maculatus), characterized in that the geometry of the lower well is configured so that only the larva hatched from the single fish embryo is capable of passing through the lower well from the upper well into the respective dock . at least one dock , each of the at least one dock defines a stepped tank comprising an upper tank and a lower tank , an inflow channel in fluid communication with the stepped tank for supplying a fluid to the stepped tank , and an outflow channel in fluid communication with the stepped tank for draining the fluid from the stepped tank , wherein the upper tank is larger than the lower tank to allow culturing of the fish larva therein, and wherein the geometry of the lower tank fits the dimension of the fish larva to reversibly receive the fish larva from the upper tank and to dock the fish larva at a controlled orientation for imaging or observation, at least one stepped well , each of the at least one stepped well comprising an upper well and a lower well , each of the at least one stepped well in fluid communication with a respective dock , wherein the geometry of the upper well is configured to accommodate a single fish embryo of the zebrafish, medaka (Oryzias latipes), antarctic fish (suborder Notothenioidei), Mexican tetras (Astyanax mexicanus), toadfish (Batrachoididae), bicolor damselfish (Stegastes partitus) or platyfish (Xiphophorus maculatus), characterized in that the geometry of the lower well is configured so that only the larva hatched from the single fish embryo is capable of passing through the lower well from the upper well into the respective dock . <EOS>