Short answers, pulled from the story.
The earliest fish appeared approximately 530 million years ago during the Cambrian explosion. These primitive creatures were small filter-feeding organisms like Haikouichthys that possessed a notochord and eyes positioned at the front of their bodies.
A typical fish gill system consists of comblike structures called filaments that contain a capillary network for countercurrent exchange. This mechanism allows fish to extract oxygen from water with remarkable efficiency even when the water is oxygen-poor.
Species such as manta rays and wrasses have demonstrated self-awareness through mirror tests by checking whether their reflection mimics their body movements. This behavior was previously thought to be exclusive to primates and some birds.
The Atlantic northwest cod fishery population was reduced to just 1 percent of its historical level by 1992. This collapse led to an economically inviable fishery that has yet to recover.
Over 65 million tonnes of marine fish are captured annually in the global fishery industry. This figure is alongside 10 million tonnes of freshwater fish and 50 million tonnes of farmed fish.