|Rawles, Steven - Steve|
Submitted to: North American Journal of Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/14/2000
Publication Date: 5/1/2000
Citation: Yesim, B., Rawles, S.D., Gatlin, D.M. Phosphorus fractions of various feedstuffs and apparent phosphorus availability to channel catfish. North American Journal of Aquaculture. 2000. v.62(3). pp.184-188. Interpretive Summary: Phosphorus is an essential mineral and must be provided in the diet of fish. Feedstuffs contain different forms of phosphorus, some less easily dissolved (soluble) in water than others. Much of the phosphorus found in plant products is chemically bound and unavailable to fish. Excessive soluble or unavailable phosphorous in fish feed enters ponds as waste and fertilizes blooms of blue-green algae. Blue-green algae not only cause water quality problems, they are consumed by fish and contain compounds that cause "off-flavor" or objectionable taste in fillets. Off-flavor is one of the most serious and costly problems in the aquaculture industry. Decreasing phosphorous waste from fish feed is a major priority of the aquaculture community. This study determined the amount of total and soluble phosphorous in ten feedstuffs and how available these forms of phosphorous (P) were to catfish. The feedstuffs tested were menhaden fish meal (Select ), meat and bone meal, fish meal analog (PROPAK ), soybean meal, cottonseed meal, corn, sorghum, wheat flour, wheat middlings, and rice bran. Total P content was highest in the animal products and lowest in the plant products. The percent of total P that was available to catfish varied from 82% in the fish meal analog to less than 35% for corn. Most of the total P (60-70%)in feedstuffs was not soluble and therefore less likely to cause water quality problems. Moreover, most of the soluble P (over 92%) was available to the fish and therefore less likely to end up in the pond. These data will help fish producers, feed mills, and scientists to formulate diets that provide enough phosphorous to maximize fish growth while minimizing the amount of phosphorous that ends up as waste.
Technical Abstract: Phosphorus is an essential mineral and must be provided in the diet of fish. Much phosphorus found in plant products is chemically bound in phytate and unavailable to fish. Some forms of phosphorous are more soluble than others. Excessive phosphorous in culture systems can result in cyanobacteria blooms which deteriorate water quality and cause off-flavor in fillets. This study determined the amount and availability of total (TP)and soluble reactive phosphorous (SRP) in ten feedstuffs to channel catfish. Test diets consisted of a 70:30 mixture of reference diet to test ingredient with chromic oxide as the inert marker. Diets were extruded under commercial conditions to produce a floating pellet(5 mm). Test diets were fed for 5 d to triplicate groups of fish (150-200g). Fecal samples were obtained by stripping 12 h postprandial and analyzed for TP and SRP from which apparent availability coefficients were calculated. Test ingredients included low temperature processed menhaden fish meal (Select ), meat and bone meal, fish meal analog (PROPAK ), soybean meal, cottonseed meal, corn, sorghum, wheat flour, wheat middlings, and rice bran. Total P content was highest in the animal products (42 to 18 g/kg) and lowest in the plant products (14 to 3 g/kg). Among the animal products, the percent of TP available varied from 82% in the fish meal analog to less than 50% for the fish meal. Among the plant products, the percent TP available varied from a high of 78% for wheat midds to a low of 34% for corn. Generally, SRP comprised 30 to 40% of TP except in corn (50% SRP) and rice bran (17% SRP). In most ingredients, over 92% of the SRP was available to catfish except in Select menhaden fish meal (63%) and wheat (44%).