Sample batches for analysis commonly consisted of 6 specimens; batches of small fish and shellfish frequently contained more, while in a few instances catches of fewer fish were analysed when insufficient suitable specimens were available. The fish were either obtained from commercial catches or from survey cruises by research vessels. Catch data were collected at the time the fish were caught. Samples were kept frozen until needed for analysis.
For analysis the fish were thawed and any resulting drip was weighed together with the fish to determine body weight. The body length from mouth to caudal fork or to rear of tail depending on the shape of the tail was recorded, and the sex of finfish was determined from the appearance of gonads. Sharks were sexed by the presence of “claspers” [3].
Each finfish was divided into 5 body parts: the head by a straight cut immediately behind the pectoral fins which left a maximum amount of flesh on the trunk; the flesh, consisting of the 2 hand skinned deboned fillets; the viscera consisting of the total contents of the abdominal cavity; the skin removed from the fillets; and the frame including belly flaps and any bones cut from the fillets. Each part was weighed and minced. Any drained liquor was added to the respective parts prior to mincing. Small body parts were cut into cubes of approximately 3mm and mixed. Fresh material from all these parts was analysed for oil (total lipids) by the method of Folch et al. [21], and moisture and ash contents by AOAC methods 80.010 and 80.012 [22] respectively.
The samples for analysis of protein, carbohydrate and urea were freeze-dried. The soluble carbohydrate content of the edible part was colorimetrically determined [28]. For the protein determination the total nitrogen content was determined [23] and the resulting ammonia measured [24]. The crude protein was calculated from total nitrogen using the factor 6.25 [25]. Sharks contain considerable amounts of non-protein nitrogen as urea [26]. To avoid over-estimation of crude protein in these species, urea was determined [27], and subtracted from the calculated protein values. The proximate composition of whole finfish was calculated from the weight and composition of its 5 constituent body parts.
Mollusc species were each bulked after shucking and removal of inedible parts, and analysed by the same methods. Squid were divided into an edible portion consisting of the flesh of mantle, tentacles and fins; and offal consisting of viscera, head and skins. The composition of whole specimens was calculated from the weight and composition of these fractions. Paddle crab were analysed whole as was the edible part consisting of the flesh of body, claws and legs. Flesh from rock lobster body, tail, legs and claws was analysed as were the viscera. Lobster krill were minced whole. Energy values were determined by calculation from the mean values of oil, protein, and carbohydrate [29].
While the analytical methods described are suitable for this laboratory they are by no means unique. Aitken et al. [30] have described different ways of measuring the proximate composition of fish which might also be suitable for industrial use.
