Re: Q1.What is the meaning of pelagic & fish staying under the condition?

Hello Kareem!

According to the online version of the Merriam-Webster Dictionary, the word "pelagic" has this definition: of, relating to, or living or occurring in the open sea. We marine biologists use the term to describe both the organisms that live there, and the habitat itself -- thus, a pelagic habitat is one that occurs away from land out in the open sea.

Tthe word "pelagic" can also refer to the vertical water column itself and the organisms that live there. In other words, there are animals that live close to shore but are considered pelagic because they live up in the water column instead of on the bottom (benthos). Animals that live on the bottom, whether close to shore or far away, are called "benthic".

The pelagic realm makes up the vast majority of the water in the oceans and differs from the inshore waters that are more familiar to us. Oceanic (pelagic) waters tend to have little input from terrestrial sources simply because they are far from land; all nutrients and organic materials are generated within the water column itself, and such waters are typically considered to be oligotrophic, or nutrient-poor. In contrast, nearshore waters receive a lot of terrestrial input due to runoff and erosion, and are generally termed eutrophic, or nutrient-rich.

To address your specific question, I'd say that fishes living under conditions of pelagic input are those that would be found in oceanic waters. In these nutrient-poor waters, fishes (and other predators) must search vast volumes of water for scarce food. For example, tunas and billfishes (swordfishes and marlins) are very strong swimmers, known to swim thousands of kilometers across entire ocean basins. Tagged northern bluefin tunas cross the Atlantic Ocean in as few as 119 days, making many sidetrips to forage as they travel. And tunas are built for high-speed endurance swimming, cruising at speeds up to 75 km/ hour!

If you wish to learn about pelagic fishes that you might find in the Atlantic Ocean near Nigeria, these sites might be helpful:

http://www.pfa- frozenfish.com/pfa2/fish1.html
http://na.nefsc.noaa.gov/lme/ text/lme28.htm

I hope this information helps!

Allison J. Gong
MadScientist

Reference: Castro, P. and Huber, M. 2000. Marine Biology, 3rd edition. The McGraw-Hill Companies, Inc.