Processing yield of Nile tilapia (Oreochromis niloticus): head cut types and two weight classes

Abstract

The aim of this study was to evaluate the best type of head cut of Nile tilapia (Oreochromis niloticus) resulting in better fillet processing yields. The experiment was carried out at the Pisciculture Station of UEM/Codapar, Maringá, Paraná, Brazil. One hundred and twenty specimens were slaughtered, head cut, eviscerated, and had their fin, skin and fillet removed. The fillet processing was undertaken by a single person. Plotting was completely randomized by a 2x3 factorial scheme. Treatments consisted of two weight categories ( W1=250-400g and W2=401-550g) and three types of head cut (C₁=oblique, OB; C₂=Contour, CO, and C₃=strainght, ST), with 20 replicates. Each fish was considered an experimental unit. Mean values of yield were expressed in relation to fish body weight. There was an influence of head cut types and weight categories on the dressed out and fillet yield. The yields in W2 (OB=50.42%, 35.27%; CO=50.70%, 35.18% and ST=48.50%, 33.82%) were higher (p < 0.05) than in W1 (OB=47.35%, 32.64%; CO=47.65%, 31.86% and ST=40.79, 27.72%) for dressed out and fillet respectively. In lower weight classes (W1), the yields of dressed out and fillet were influenced (p < 0.05) by the type of head cut, where ST had lower yield compared with OB and CO. The yields of carcass without head (61.91%), ventral abdominal muscles (2.85%), deep hipaxial muscles (4.72%) in W2 were higher (p < 0.05) than those in W1 (57.13%; 2.45% and 3.75%) respectively as for the characteristics analyzed. Furthermore, weight category had no influence on percentage of skin and other residues, except for percentage of head (p < 0.01). As for head percentage, W1 was significantly higher (30.67%) and W2 was significantly lower (27.07%). On the other hand, the yield and by-product percentages were influenced (p < 0.05) by head cut type, with CO showing better yields for carcass without head (62.47%) and ventral abdominal muscle (4.33%) and skin percentage (5.99%); and lower head percentage (24.79%) when compared with OB and ST. There was no influence of the head cut on deep hipaxial muscle ((OB=4.01; CO=4.36% and ST=4.03%). The results suggest that, under these conditions of filleting, fish with 400g body weight or more are the most recommendable for slaughter, and CO and OB are indicated to improve dressed out and fillet yield in tilapia.