Pelagic: Open Ocean Fish

Ahoy there landlubbers! Todays catch are pelagic fish species, meaning fish that are found away from the shore. The open ocean accounts for almost two thirds of our planets surface and is habitat for eleven percent of all marine species. Its an immensely vast area that we know very little about and survival is often times extremely difficult. Many fish in the environment have special adaptations which allow them to be successful. The fish range from the small nearshore bait fish; sardines and herring, to the powerful bluefin tuna and oceanic sharks. Particular species that draw our interest are the large ocean hunters including the billfish and tunas.

These massive fish have lots of obstacles to overcome to make it in basically a marine desert. Their large size comes at the cost of developing tremendous power to propel them through the water, sometimes for Marlin upwards of 60mph. Tuna have incredible muscle composition, having higher concentrations of red muscle which allows them to cruise at high speeds for extended periods of time. Bodies of fish have either red or white muscle. The red muscle (densely packed with blood) is what will allow fish to maintain speed for a while. Whereas the white muscle is what allows fish quick burst of speed. Tunas and marlin are also the closest fish to being independent of the environment temperature wise and are shown to alter their body temperature dependent on the external environment. Pretty crazy stuff to think that fish have come close to something we mammals take for granted!

Many open ocean fish have many physical characteristics that allow them to be the kings of their open ocean playground. the main way this is done is be retracting their fins when in pursuit of prey. Tuna and marlin have special slots along their bodies for their fins to slide into giving thus almost eliminating drag and giving the fish almost the complete shape of a torpedo shooting through the water. And if you’ve ever seen a fish from this environment close up you will notice an interesting keel shape near their tails. This acts to stabilize the fish and minimizing water resistance. Fish in this environment have completely fascinated people for many years and there is still so much to learn from them. With overfishing and by catch a major issue for many species in this are (due to high economical value) many scientists predict a sharp decline in numbers of individuals. Marlin and Tuna are amazing animals with amazing adaptations making them the true rulers of the Pelagic environment.


We would like to thank you for visiting our blog. Catalina Island Marine Institute is a hands-on marine science program with an emphasis on ocean exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and ocean happenings. This blog has been created by our staff who have at least a Bachelors Degree usually in marine science or related subjects. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science and ocean information. Feel free to leave comments, questions, or share our blog with others. Please visit for additional information. Happy Reading!