Supplemental feeding of fish is an interesting and often discussed subject on the Pond Boss Forum. You should go see for yourself the many questions, ideas, and approaches being used. One thing is clear; feeding programs take many different forms and are as varied as pond owners and locations. The science basics of growth through feeding are simple.
Water, dirt, and sunlight come together and lead to plant (plankton) growth and photosynthesis. This is the base of the food chain. Fish, being living organisms, obtain energy from eating these organic materials for energy and growth. These are mostly carbohydrates, fats, and proteins. The amount of energy actually obtained by the fish is lower than the amount present in the food; there are losses in digestion, metabolism, and thermogenesis. In short, there is an Energy Budget—Inputs = Outputs + Growth.
Because fish growth often is limited by food availability, supplemental feeding is a logical tool to improve the condition offish in small impoundments. The question then becomes many times more complicated, because the immense variety of cultured fish species hampers efforts to simplify production of feed (pellets) industry wide. Approximately 170 types of fish are currently cultured, including carnivores like bass and trout, herbivores such as tilapia, planktivores including shad, and omnivores, one being catfish, each having its own set of nutritional demands.
There is a multitude of information available about species food needs and results, but no one feed that can meet the needs of all types of pond fish. That is where individual goals, including what fish you want, come into play. One key factor is how much your fish will rely on pelleted feeds. Will it be just a little supplemental feeding or extensive feeding for rapid growth? It makes a difference on all aspects of how a pond is managed.
Here are a few findings from some older studies which address some basics. The energy cost for bluegill to feed on pellets is small relative to the high caloric intake, which can be 4-5 times greater than those fed just natural foods, Schalles and Wissing 1976.
The rate of growth of sunfish can be increased by short-circuiting the food cycle, thereby producing harvestable size sunfish in a shorter period of time than would occur under natural conditions, Carnes 1966.
Results indicate that total fish production and production of bluegill were each increased approximately 75 to 80% by supplemental feeding in 19 months after stocking, Schmittou 1967.
In lakes, pellet feeding has been found to increase the number of large bluegills, Nail and Powell 1975.
Feed in excess of 10 pounds-per-acre, per-day in ponds was not utilized. Some accumulated and decomposed, thus depleting the supply of dissolved oxygen, which resulted in fish kills, Schmittou 1967.
The pellet size should be approximately 20- 30% of the size of the fish species mouth gape. Feeding too small a pellet results in inefficient feeding because more energy is used in finding and eating more pellets. Conversely, pellets that are too large will depress feeding, and in the extreme, cause choking. Select the largest sized feed the fish will actively eat. Addition of supplemental pelleted feed did not contribute to the rate of growth of young shad, but did increase the growth and spawning frequency of adults.
Largemouth bass preferred fish and other animals (64%), but also ate some supplemental feed (32%). Bluegill stomachs contained more supplemental feed (44%) than any other item, followed by insects and animal parts (28%), and plant parts (17%). Redears seemed to prefer insect larvae (42%), but also ate plant material (38%). White amur apparently did not compete with the sunfishes for either natural or supplementary food items. Addition of supplemental pelleted feed did not contribute to the rate of growth of young shad, but did increase the growth and spawning frequency of adults, Kilgen 1974.
With those basics in mind, it is important to understand a little about fish nutrition. The basic components are carbohydrates, fats, and proteins, but minerals must also be considered. Fishmeal has proven to be an excellent dietary protein source for fish, leading to its description as an ideal protein. The ideal protein concept is based on the premise that if the amino acid profile of the feed mimics the whole-body amino acid profile of the animal being fed, protein utilization and growth should be maximized. Lipids, fatty acids, and their derivatives play a role in virtually every physiological process that occurs, and for this reason dietary lipid composition and content represent a massive sector of overall nutrition. Nowhere is this truer than in fish nutrition where lipid can exceed protein in the body composition of fish, a testament to the physiological and energetic importance of this nutrient class, Tocher 2003. Aside from physiological importance, lipids are indispensable energy sources, especially for finfish, which are not well-adapted to carbohydrate utilization.
Dietary protein and energy must be kept in proper balance, because a deficiency or excess of dietary energy can reduce growth rates. Fish fed diets deficient in energy will metabolize more expensive dietary protein to meet energy requirements. Excess dietary energy can decrease protein intake and suppress growth.
Most pond fish do not require carbohydrates in their diet—complex carbohydrates cannot be digested and utilized efficiently by most of these species. For this reason, diets fed to carnivores and most pond species rarely contain more than 20% complex carbohydrate. The exception among predator fish is hybrid striped bass, which can digest carbs and can become obese on standard fish foods. Conversely, warm water omnivores or herbivores (e.g., channel catfish, tilapia, common carp, and white sturgeon) adapt well to diets containing as much as 40% dietary carbohydrate.
Although vitamins and minerals are required in minute amounts compared with protein, lipid, and so forth, they are critically important—every micronutrient has a deficiency disease associated with it, the effects of which are sometimes irreversible or fatal. For a few vitamins and most minerals, excess can be equally detrimental, resulting in toxicity.
Most fisheries experts will tell you that over the long-term, natural forage is necessary. Fish do not survive well over long periods on just pelleted food. Many times, the question asked is what natural source is best for predator fish. There is no single best answer, but the nutritional values of some major forage species exist. Mean fat percentage of shads (24.2%) exceeded that of bluegill (15.2%) and fathead minnows (19.1%), but was less than that of mosquitofish (25.8%) and golden shiners (34.8%). Bluegills had lower caloric contents than gizzard and threadfin shad. Data collected for one study also showed bluegill to have lower caloric content than the shads.
With the basics behind us, next time we will review some more recent studies that build on these concepts. In the meantime, visit the Pond Boss Forum and join in the discussion.
Reprinted with permission from Pond Boss Magazine
