RESULTS

The number of finfish per batch together with the size, sex and catch data are shown in Table 1. Virtually all species mentioned in current domestic landing data are included, as are many from the deep sea fisheries by-catch which could be of commercial value in the future.

To avoid the traditional confusion created by common fish names in different fishing areas the nomenclature in Ayling and Cox [3] has been used except when a generally used name of species has become more popular, e.g. black oreo for spiky oreo. Also the scientific name for each species has been added. The fishing return area numbers are those used by the Ministry of Agriculture and Fisheries [31]. These areas are shown on page 14.

Some species have been studied over a 12 month period or in considerably larger numbers during a catching season than Table 1 indicates. These include trawled jack mackerel, hoki and red cod [4], purse seined jack mackerel and blue mackerel [5], skipjack tuna [7], and squid species [9].

Table 2 shows the proportion of body weight of the dissected fish by the 5 constituent parts. Differences between individual fish were generally greatest in skin and viscera. Hand skinning and loss of scales could account for the variations in the skin; visceral differences were mainly due to gonad size and the quantity of ingesta.

Table 3 gives the proximate composition of the 5 body parts and whole finfish. Data on carbohydrate were omitted because the levels measured were small and differed little between species or between specimens within a batch. The proportions of soluble carbohydrate in the fillets ranged between 0.15-0.25% of wet weight. These values compare closely to those given by Jacquot [33].

A ready method to arrive at the oil content of the fillet consists of determining its moisture content, and calculating the oil content by subtracting the moisture content from the sum of the moisture and oil contents given in Table 3. The sum of these two values is regarded as constant for most practical purposes [34]. The statistical relationships between the moisture and oil contents of the flesh of some species with large variations in oil content have been determined by linear regression:

Table 4 shows the proportions of protein, oil, moisture and ash in the whole fish contained in the 5 constituent parts. The data were compiled from the mean values given in Tables 2 and 3, and together with the composition of the whole fish (Table 3) can be used to calculate the proximate composition of edible products and offal from any body parts cited resulting from a given weight of fish.

For instance Table 3 indicates that 100 tonnes of orange roughy contain 17.6 tonnes of oil. Of this quantity 55.1% (44.1 + 11.0) or 9.7 tonnes is present in the heads and viscera (Table 4). The fillets account for 20.6% or 3.6 tonnes.

The frames and skins contain 24.3% (15.9 + 8.4) or 4.3 tonnes, which comprise landed offal from fish headed and gutted at sea.

Table 5 gives the catch and harvesting data of the Crustacea and shellfish, and Table 6 gives the proximate composition of their edible parts together with the composition of offal and whole bodies of some relevant species. Soluble carbohydrate concentrations were found to vary considerably between these species, so these data have been included in Table 6. It is not known what influence carbohydrates have on flavour. The principal carbohydrate in fish (glucose) is not very sweet [36], and flavour appears mainly due to the presence of non-protein nitrogenous compounds [37].

The calculated energy values of the edible parts of all species discussed are shown in Tables 7 and 8. These data should be useful in calculations of the nutritive value of diets in which one or more of the fish are included. The oil content of orange roughy, black oreo dory and smooth oreo dory consists of more than 90% wax-esters [38]. As it can be assumed that the wax esters are not digested by man to any extent (D.H. Buisson pers. comm.), their inclusion in energy calculations would lead to misleading results. For this reason the calculations for these 3 species were not based on the total oil content but on the non-wax-ester fraction only.