Barometric Pressure Affects on Fishing Part III

[Bonefish]

Swimbladder pressure control works on osmoregulation. Swimbladders with "gas glands" can introduce gases into the bladder to increase volume and buoyancy. When buoyancy is maintained, it allows the fish to change depths without having to waste energy when swimming trying to keep upright. To reduce buoyancy in a closed-system swimbladder, gases are released from the bladder into the blood stream and then expelled into the water through the gills. In order to introduce gas (mainly pure oxygen) into the bladder, the "gas gland" excretes latic acid, and the resulting acidity causes the hemoglobin (Hgb) of the blood to lose its oxygen, which then diffuses into the bladder while flowing through a complex capillary cluster structure known as the "rete mirabile." The "rete mirabile" is a network of cross-current arteries and veins that keeps oxygen from leaving the veins At a similar structure known as the "oval window", the swimbladder is in contact with blood and the oxygen can diffuse back. Fish with "gas glands" cannot rise from deep water very fast because the bladder equilibrium doesn't occur quickly. However, a fish may quickly come to the surface and return without acute adjustments in bladder volume. In some freshwater fish, the gas bladder is connected to the inner ear by the "Weberian apparatus", which provides a precise sense of water pressure and depth and may even improve hearing.

Gass passes through the "gas gland" filled with arterial blood in front of the swimbladder, and gas leaves the bladder through an oval body filled with venous blood in the back of the swimbladder. "Gas gland" cells are specialized for production and secretion of acidic metabolites and convert glucose to lactate along with the production of carbon dioxide. From the "rete mirabile", giant secretory cells secrete lactate, and increased lactate levels then lower the surrounding pH, causing the blood hemoglobin to dump off its oxygen. The oxygen diffuses back into the incoming capillary, increasing the partial pressure of oxygen in the incoming capillary. This continues until the partial pressure of oxygen in the capillary is higher than that of the swimbladder, which has a high oxygen concentration. This complex system is necessary because the concentration of oxygen is higher in the swimbladder that it is in the blood, so simple diffusion would tend to pull the oxgyen out of the bladder instead of pushing it in. If the fish wants more buoyancy, it must tell its secretory cells to release more lactate. Since oxygen diffuses easily with oxygen-poor venous blood, the gas can be forced out. Fish that migrate vertically tend to have high oxygen levels in their bladders because oxgyen transport is faster. Fish that maintain a stable depth tend to have more nitrogen because it is inert, enters slowly and exits slowly. All of this makes you think who could of thought of all this complex system just for a fish bladder. Next we will continue to discuss buoyancy in Part IV.

[buzzking]

In the words of Chris Farely...."Do you want my HEAD TO EXPLODE? In the name of all that is good and decent....NO MORE FOR TODAY!"

[Bonefish]

Sorry, BuzzKing! Its painful I know!