Question

what does aquatic life produce as a byproduct when consuming dissolved oxygen? ozone nitrogen gas hydrogen gas carbon dioxide

Explanation:

Aquatic life (like fish, bacteria, etc.) undergoes respiration, similar to other organisms. During respiration, they consume oxygen ($O_2$) and break down organic matter (or use stored energy). The process of aerobic respiration produces carbon dioxide ($CO_2$) as a byproduct. Ozone ($O_3$) is not a byproduct of aquatic respiration. Nitrogen gas ($N_2$) and hydrogen gas ($H_2$) are not typical byproducts of consuming dissolved oxygen in aquatic respiration.

Answer:

carbon dioxide