Effect of dietary fish meal levels on environmental phosphorus loading from carp culture

Abstract

SUMMARY: The present study was carried out to reduce the total phosphorus loading (T-P) from carp by replacing dietary fish meal with alternate proteins (blood meal and defatted soybean meal). The experimental diets were formulated according to the Lake Kasumigaura Standard (crude protein 3.5 kcal/g) and contained fish meal at the levels of 10, 15, 20, 25, and 30%. The dietary total phosphorus (P) contents were between 0.9 and 1.4%, and water extractable P (available P for carp) ranged from 0.55 to 0.70%. Duplicate groups (n = 50) of carp (average weight 2.2 ± 0.3 g) were fed one of the five experimental diets to satiation, three times a day for 12 weeks, at 20.0 ± 1.6°C. T-P from each group was determined based on water extractable P and the rate of P absorbed and retained in carp. The growth performance was highest in fish fed the diet containing 25% fish meal followed by 30%, although there was no marked difference between the treatments except for the 10% fish meal group. The feed gain ratio ranged between 0.96 and 1.14. The values for T-P (kg/t carp production) were effectively reduced by decreasing dietary fish meal levels, and ranged from 5.9 for the 10% fish meal diet to 9.6 for the 30% fish meal diet. However, low fish meal diets with high amounts of alternative proteins resulted in high nitrogen loading, therefore, a suitable level of fish meal in carp diet was estimated to be 20–25%, under the present feeding conditions, substituted by a combination of blood meal and defatted soybean meal.