RAW-MATERIAL FRESHNESS, A QUALITY CRITERION FOR FISH-MEAL FED TO SHRIMP

Raw material freshness is an important criterion of fish-meal quality for salmonids and also for swine and broiler starter feeds, but needs to be assessed for shrimp. Three batches of anchovy meal were produced in a commercial low-temperature processing plant in Chile, from a uni que source of raw fish, either fresh (FR, 12 h post capture), moderate ly fresh (MF, 25 h post capture) or stale (ST, 36 h post capture). Fre shness was assessed through the total volatile nitrogen content in fis h before process (TVN 14, 30 and 50 mg N/100 g, respectively), and bio genic amines in fish meal (histamine 28, 1850 and 4701 mg/kg, respecti vely, and also with increasing content of cadaverine, putrescine and t yramine). Samples of the three fish meals were incorporated at levels of 30% or 40% into isoenergetic diets fed ad libitum to shrimp during various feeding trials. Feeding trials were conducted in Monterrey, Me xico, on Penaeus vannamei early juveniles (0.9 and 1.5 g initial weigh t) held in a synthetic seawater recirculating system, and in Tahiti on P. vannamei (7.6 g), P, monodon (2.5 g) and P, stylirostris (8.4 g) i n a natural seawater flow-through system. Small P, vannamei (0.9 g) ex pressed significantly higher feed consumption (P = 0.028) and percent weight gain (P = 0.048) when fed the fresh raw material fish meal: gro wth increased by 25% compared with the moderately fresh and stale raw material treatments, but no significant differences were detected in f eed conversion, nor survival. Larger P. vannamei (1.5 and 7.6 g) did n ot show any significant response. P. monodon had a tendency to better growth with the FR treatment (non significant, P = 0.109). Finally, P. stylirostris late juveniles (8.4 g) fed the FR feed showed a highly s ignificant increase in weight gain (P = 0.007), but also a poorer feed conversion (P = 0.004). A global interpretation of this set of result s could be that susceptibility to raw-material spoilage would be highe r in species with carnivorous tendencies (like P. stylirostris, known for its higher protein requirement), and also in young stages of less carnivorous species (as in the case of 0.9 g P. vannamei). However, ra w material freshness, as indicated by TVN levels in raw material (less than 30 mg N/100 g) or by the sum of amine contents in the final prod uct (less than 2000 mg/kg), is a duality parameter that should be cons idered when selecting fish meal for shrimp diets, particularly for ver y young juveniles and carnivorous specie;. (C) 1998 Elsevier Science B .V. All rights reserved.