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 unique source of raw fish, either fresh (FR, 12 h post capture), moderately fresh (MF, 25 h post capture) or stale (ST, 36 h post capture). Freshness was assessed through the total volatile nitrogen content in fish before process (TVN 14, 30 and 50 mg N/100 g, respectively), and biogenic amines in fish meal (histamine 28, 1850 and 4701 mg/kg, respectively, and also with increasing content of cadaverine, putrescine and tyramine). 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, Mexico, on Penaeus vannamei early juveniles (0.9 and 1.5 g initial weight) 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) in a natural seawater flow-through system. Small P. vannamei (0.9 g) expressed significantly higher feed consumption ( P=0.028) and percent weight gain ( P=0.048) when fed the fresh raw material fish meal: growth increased by 25% compared with the moderately fresh and stale raw material treatments, but no significant differences were detected in feed conversion, nor survival. Larger P. vannamei (1.5 and 7.6 g) did not 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 significant increase in weight gain ( P=0.007), but also a poorer feed conversion ( P=0.004). A global interpretation of this set of results could be that susceptibility to raw-material spoilage would be higher 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, raw 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 product (less than 2000 mg/kg), is a quality parameter that should be considered when selecting fish meal for shrimp diets, particularly for very young juveniles and carnivorous species.