No abstract

Rainbow trout with initial body weight 1144 g were fed two diets with high (feed A) or low (feed B) water stability for 6 weeks. During the last 2 weeks either stable or fluctuating oxygen saturation, salinity and temperature was introduced. High water stability of the feed was associated with harder pellets, less dust formation and less broken pellets compared to feed with low water stability. During the first 4 weeks, feed intake was 23% higher in trout fed diet B than in those fed diet A. Fluctuating environment resulted in a severe drop in feed intake for both dietary groups. At termination of the trial, stomachs of trout fed feed B contained mashed pellets and free water and oil. Stomachs of trout fed feed A contained more intact pellets and little fluid. The apparent digestibility of protein, starch, dry matter and energy was highest in feed A. The apparent digestibility of P and Zn was highest at stable environment, and the absorption of P was highest from feed A. In conclusion, physical quality affected the nutritional value of the feeds, and differences in nutritional value at stable or fluctuating environment appeared to be related to feed intake.

No abstract

Management of nitrogen (N) in rice-fish culture is of great significance in order to exploit synergies between rice and fish. However, detailed and systematic studies on N cycling in rice-fish systems are rare. An experiment was carried out at the Bangladesh Agricultural University using the fish species common carp, Cyprinus carpio L., and Nile tilapia, Oreochromis niloticus (L.). Efficiencies of fertilizer and feed as N inputs were evaluated by establishing an apparent N balance. The different N input strategies for rice-fish (RF) treatments were:(1) with fish, with urea (101 kg N ha À1 , RF Urea), (2) with fish, with feed (22.6 kg N ha À1 , RF Feed I), and (3) with fish, with feed (41.5 kg N ha À1 , RF Feed I I ) . R i c e o n l y ( v a r . B R 2 8 ) w i t h u r e a (101.2 kg N ha À1 ) was added as the control (Rice only). Urea as N input (Rice only, RF Urea) resulted in negative apparent N balances (N output-N input), whereas N input in the form of feed (RF Feed I, RF Feed II) led to positive apparent N balances due to the lower N input. The presence of fish increased the grain and straw N output in RF Urea compared to Rice only, the effect being significant for straw (P < 0.05). Moreover, a significant difference in nitrogen uptake by rice was seen between the two feeding levels. The higher feeding rate in the RF Feed II treatment led to higher N outputs of grain, straw and fish compared to the RF Feed I treatment, a significant difference occurring for straw (P < 0.05). An apparent recovery efficiency of 48.7% was determined for the additional N input in RF Feed II compared to the RF Feed I teatment. An economic analysis revealed that the RF Urea treatment was the most profitable, as reflected by the highest gross margin. In conclusion, the results indicate that fish can improve nitrogen uptake by rice plants. Moreover, the supply of supplementary feed has a fertilizing effect on the rice due to the utilization of excreted feed nutrients by rice plants.

Feed pellets in modern aquaculture must be of high physical quality to withstand mechanical impacts. However, physical quality of feed has been shown to affect nutritional responses. In the present study, different moisture contents were used to modify physical feed qualities.Effects of dietary moisture content on physical feed quality, feed intake, nutrient digestibility and growth performance in Atlantic salmon were investigated. Different drying times of four commercial-like extruded diets resulted in in dry matter contents of 95.9%, 94.1%, 92.3%, 90.8%. A fifth diet containing 70% dry matter was made