Hi Byron, I'm still very new to this, I just wanted to ask why more fish would have less impact on the tanks biological systems?
I've posted about this several times in the past, because it is something many fail to understand. I'm useless at finding old threads, so will summarize here for you and others. Some is cut and pasted from an article I wrote a few years back.
Each species of freshwater fish has evolved to function best in a
very specific environment. The "function" refers to the homeostasis. Homeostasis is defined as “the tendency of an organism or a cell to regulate its internal conditions, usually by a system of feedback controls, so as to stabilize health and functioning, regardless of the outside changing conditions.” Physiological homeostasis, or physical equilibrium, is the internal process animals use to maintain their health and life: “the complex chain of internal chemical reactions that keep the pH of its blood steady, its tissues fed, and the immune system functioning” (Muha, 2006).
We need to understand what "very specific environment" means too. This includes the water parameters (hardness, pH, temperature); the physical surroundings (type of substrate, rock, wood, plants, light intensity, water current); the number of fish in the species (extremely important for a shoaling species); other species within the area, which becomes very important in the confines of any aquarium; and with respect to thee aquarium, the actual physical space itself. All of these factors have an impact on individual fish. This is why community tanks can be challenging...every species added has to "fit in" with all the others with respect to all of these factors.
This greater dependence upon their surrounding environment is why fish are more susceptible to stress than many other animals (Wedemeyer, 1996). All of the above "expectations" or "needs" are programmed into the DNA of each species. We cannot change it; only evolution and nature can do that, and it takes hundreds to thousands of years. Dr. Paul Loiselle (an acknowledged authority in ichthyology and this hobby) sums it up in the green citation in my signature block. This must absolutely never be forgotten if we want healthy fish, because it is at the core of their health.
Stress attacks the immune system and the homeostasis of the fish. If any of the above factors is missing, the fish will experience stress because of it, always. Stress is the direct cause of 95% of all fish disease in an aquarium. That is pretty significant. Various pathogens may be present, but it is the stress that weakens the fish and they then succumb to the disease.
Stress is caused by placing a fish in a situation which is beyond its normal level of tolerance (Francis-Floyd, 1990). Stress makes it more difficult for the fish to regulate the normal day-to-day physiological functions—the homeostasis—that are essential to its life. When fish are under stress from any of the above factors being missing or inappropriate, their impact on the biological system is increased. The effects of stress on fish are very complicated physiologically, and are often subtle. There may or may not be external signs discernible to us—it can continue for weeks and even months, sometimes up to the point when the fish just suddenly dies. The reasons for this are involved.
Adrenaline released during the stress response increases blood flow to the gills to provide for the increased oxygen demands of stress. The release of adrenaline into the blood stream elevates the heart rate, blood flow and blood pressure. This increases the volume of blood in vessels contained within the gills, increasing the surface area of the gills to help the fish absorb more oxygen from the water. The elevated blood flow allows increased oxygen uptake for respiration but also increases the permeability of the gills to water and ions. This is what is known as the osmorespiratory compromise (Folmar & Dickhoff, 1980; Mazeaud et al., 1977). In freshwater fish, this increases water influx and ion losses. This is more critical in small fish than larger due to the gill surface to body mass ratio (Bartelme, 2004).
I've tried to explain this but there is much more to the story. Hopefully this helps.
