Question

When fishing boats pull trawling nets through the water, mamy fish avoid being caught by vigorously swimming away. Others, after vigorous escape swimming get caught, but later are released because they are not of legal sine or are not the species desired. Fish that escape or are released sometimes die arrway. The accumulation of lactic acid from anaerobic work in such fish seems in certain cases to be a key factor in their deaths. How could a large lactic acid accumulation in a fish interfere with its ability to obtair enough \(\mathrm{O}_{2}\) to survive?

Short answer

The accumulation of lactic acid in fish after vigorously swimming can interfere with its ability to obtain sufficient oxygen. Lactic acid, being an acid, can lower the pH of the fish's system, reducing hemoglobin's ability to bind and transport oxygen efficiently. This ultimately results in the fish not receiving enough oxygen to survive.

Step-by-step solution

Understanding Lactic Acid Buildup

When fish swim vigorously, they switch from aerobic respiration (involving oxygen) to anaerobic respiration due to the increased energy demand. During this process, there is a buildup of lactic acid, which results from the fermentation of glucose in anaerobic conditions. The more the fish swims, the more lactic acid is produced.

Effects of Lactic Acid Buildup

This accumulation of lactic acid is not immediately problematic, but if the fish does not have a chance to recover, this will lead to muscle fatigue and potential system failure. Lactic acid is an acid and will therefore lower the pH in the animal's body upon accumulation.

Interference in Oxygen Absorption

The problem arises when a fish's system becomes increasingly acidic due to the presence of lactic acid. If the pH of a fish’s internal environment drops significantly, it could interfere with the fish’s ability to bind and transport oxygen efficiently. Oxygen is transported in fish through hemoglobin in red blood cells. However, oxygen's binding affinity to hemoglobin diminishes as acidity increases, resulting in less oxygen being transported throughout the fish's body.

Key concepts

Lactic Acid Buildup

When fish engage in vigorous swimming, especially in scenarios like escaping fishing nets, they transition from aerobic respiration to anaerobic respiration. This shift is crucial because aerobic respiration cannot meet the sudden high energy demand. During anaerobic respiration, glucose is broken down without oxygen, leading to the production of lactic acid as a byproduct. The accumulation of lactic acid in muscle tissues is a natural response during intense physical activity.

However, if the fish continue this high level of activity without sufficient recovery, lactic acid levels can become excessive. This buildup can lead to muscle fatigue, making it difficult for the fish to keep swimming and evade threats. More seriously, high levels of lactic acid lead to a drop in the body's pH level, resulting in an acidic environment. It is this acidic condition that poses further challenges to the fish's health and survival.

Oxygen Transport in Fish

Fish rely on an efficient system to transport oxygen throughout their bodies, primarily through their blood. Oxygen transport is critical for maintaining metabolism, especially during periods of high activity. When a fish's tissues become acidic due to excessive lactic acid, this affects how oxygen is carried and delivered by hemoglobin in red blood cells.

In a healthy environment, oxygen diffuses from water into a fish's bloodstream via the gills, where it binds to hemoglobin. This binding process is essential for transporting oxygen to every cell in the fish's body, ensuring each cell gets the energy it needs to function effectively. However, the efficiency of this process can be compromised when the internal pH drops. The acidic conditions can impede the fish's ability to absorb and utilize oxygen appropriately, causing stress and potentially leading to a decline in overall health.

Hemoglobin Affinity

Hemoglobin, a crucial protein found in fish blood, plays a vital role in oxygen transport. It binds oxygen molecules to carry them from the gills to the rest of the fish's body. The binding and release of oxygen molecules are greatly influenced by the pH level of the blood, a relationship described by the Bohr effect.

Under normal conditions, hemoglobin has a higher affinity for oxygen in the gills, where the environment is cooler and less acidic. This allows effective binding of oxygen molecules. Conversely, as the blood circulates and reaches warmer, more active tissues, which naturally have a higher concentration of carbon dioxide and possibly lactic acid, the oxygen affinity decreases, facilitating oxygen release where it's needed most.

In situations where lactic acid buildup significantly lowers the pH, hemoglobin's affinity for oxygen diminishes even in the gills. This condition makes it challenging for fish to transport adequate oxygen, further exacerbating stress from lactic acid buildup and potentially leading to hypoxia, or oxygen deprivation.