Question

A researcher is trying to understand the distribution of a particular species of freshwater fish. The fish, a small tetra, occurs in slowly-moving streams with abundant vegetation, and is absent from streams lacking vegetation.

She is interested in knowing whether biotic or abiotic factors influence the distribution of this fish, or both.

In her first series, she sets up the following.

She creates sixteen wire enclosures, and places them in two different river environments. Eight are placed in slow moving areas with heavy vegetation. The other 8 are placed in rapidly-moving areas with few plants. She stocks all the cages with 24 fish, each of which was weighed. She returns 24 days later.

In all 8 of her center-stream enclosures, all 24 fish survived. In her vegetation-heavy enclosures, 2 cages lost one fish each.

The mean weight gained by the fish was actually much HIGHER all of the center-stream enclosures, compared to the others.

Anecdotally, she notices predatory killifish circling the center-stream enclosures, but not the othes.

What is going on here? What do these results show? What might you suggest next?

Answer 1

Comparing the Biomass growth in the fishes we find out that fast-moving water is ideal for the growth of the fishes since the weight increase is higher. we must also consider the reason behind this. Since the vegetation is less in the fast-moving central waters the only reason for the higher body mass could be that the fish is getting even more nutrition in the fast-moving waters, which could only bring more living organisms, i.e. the fish is omnivores. In fast-moving water, it is getting both green vegetation and flesh of other organisms to eat. The enclosures might be arresting some small organisms into the cage.

Next, to determine if our theory that the fish is omnivores, we must infest the cage with possible organisms of the stream. Also if the Kili fish is a predator of our Tetra must be determined as it would count as the biotic factor that affects our Tetras.