Means and methods for reducing phosphorus secretion by fish

A fish feed or fish feed additive comprising one or more polypeptides having a phytase activity, wherein said phytase activity comprising EC:

• 3.1.3.26 (i.e., 4-phytase) and/or EC 3.1.3.8 (i.e., 3-phytase) and/or EC 3.1.3.72 (i.e., 5-phytase) phytase activity, wherein said phytase activity is dosed at a level which is at least 10% (e.g., at least 15%, at least 20%, at least 25%, at least 30% or at least 35%) less than an efficient dose of phytase activity for maximizing fish growth response and/or weight gain, preferably wherein said phytase activity is dosed at a level about 500 (e.g., corresponding to “PHY500” diet as shown in Example 1 herein) to about 2000 (e.g., corresponding to “PHY2000” diet as shown in Example 1 herein) phytase activity units (FYT) per kg fish feed, further preferably wherein said phytase activity is dosed at a level about 500 (e.g., corresponding to “PHY500” diet as shown in Example 1 herein) to about 1000 (e.g., corresponding to “PHY1000” diet as shown in Example 1 herein) phytase activity units (FYT) per kg fish feed.