Barometric Pressure Affects on Fishing Part IV

Have you ever caught a bass and wondered why its eyes are bulging out? It is because you have brought the fish from deep water with greater pressure to the surface of less pressure, and the swimbladder has expanded, thus pushing against the back of the eyes. As a fish is brought up to the surface from deep water, the decrease in atmospheric pressure causes the internal organs to push outward because the fish cannot compensate for sudden changes in pressure. This can cause the bladder compensation mechanism to malfunction. A fish's buoyancy bladder is used to keep the fish upright and to maintain buoyancy in whatever depth the fish swims. A swimbladder allows the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend or desend without having to waste energy. The function of the swimbladder is to maintain a gas-filled space inside the body cavity of the fish and vary the volume of gas in response to changing hydrostatic pressure changes.

Buoyancy essentially boils down to managing a series of fluxes into and out of the swimbladder, which can be explained by a simple gas differential equation. The equation states that any given differential in moles of gas contained within the swimbladder is equal to the sum of differentials of moles of gas added to the swimbladder and removed. This is a straightforward statement of the law of conservation of mass. Generally, the inward flux of gas involves work of some type, and in this instance, the "gas gland" drives almost pure oxygen into the bladder againist considerable pressure. The efflux (removeal) of bladder gas is a managed passive process. In the physostomous bladders, the efflux occurs through the esophageal duct, which can be closed off by various smooth muscle sphinters. In the physoclistous bladder, the efflux is managed through the "oval." When the "oval" is perfused, oxygen will flow passively into the blood, driven by the large partial pressure gradient in oxygen from the swimbladder to the blood.

Volume regulation, and hence buoyancy, therefore entails regulating the molar quantity of gas contained with the the swimbladder. If the volume of a swimbladder has been compressed by increased hydrostatic pressure, it can be restored to its target volume by adding some molar quanity of gas to the bladder. Similarly, if the swimbladder's volume is too great, it can be adjusted back down by reducing the molar quanity of gas contained. Fish don't regulate bladder volume during short-term vertical migration. That is why a fish will come from twenty feet down for a lure but quickly return to their comfort zone.

If carp want to maintain neutral buoyancy intending to swim at a certain depth, they will have to gulp enough air from the surface to attain neutral buoyancy at that depth. Each change in depth will require a trip to the surface for more air. Every adjustment to a decrease in depth requires a release of gas directly into the water from the mouth. If a bass wanted to maintain neutral buoyancy in the same situation, the swimbladder gas volume would be increased or decreased entirely through secretion or resorption of gasses from or to the blood.

Hearing is the most effective mechanism for long-range communication under water. Pressure waves of acoustic energy are the most effective means of interaction amoung fish. Fish make sounds in the water either by a stridulatory mechanism or by a swimbladder mechanism. Stridulatory sounds are produced by friction of teeth, fin spines, or bones rubbing or grinding against each other. Swimbladders sounds are either indirect or direct. Indirectly, swimbladders act as a resonator (amplifier) to change the quality of the sound emitted by some other organ. Directly, swimbladders make underwater sounds either by belching gas from the bladder or of specialized muscles that cause the bladder to resonate (drumming) through body tissue.

In marine fish, water is continually leaving the fish's body through it skin and gills. To keep the fish hydrated, a marine fish drinks large amounts of water and produces small amounts of concentrated urine, and its gills are adapted to secrete salt. The tissue of the marine fish is less salty than the surrounding water. The tissues of a fresh water fish are saltier, than its surrounding environment. Freshwater fish don't drink water, and they produce large amounts of dilute urine. Water is continually entering the body of a freshwater fish through its skin and gills.

Bonefish, very good threads you've posted. Is their anyway when u get finished you could put out a post of everything u just described in a nutshell? Like a cliff notes version. If not no big deal, thanks for the post.

I will try to do that.