Geoff J. Gooley

Traceability and discrimination among differently farmed fish: a case study on Australian Murray cod.

The development of traceability methods to distinguish between farmed and wild-caught fish and seafood is becoming increasingly important. However, very little is known about how to distinguish fish originating from different farms. The present study addresses this issue by attempting to discriminate among intensively farmed freshwater Murray cod originating from different farms (indoor recirculating, outdoor floating cage, and flow through systems) in different geographical areas, using a combination of morphological, chemical, and isotopic analyses. The results show that stable isotopes are the most informative variables. In particular, delta(13)C and/or delta(15)N clearly linked fish to a specific commercial diet, while delta(18)O linked fish to a specific water source. Thus, the combination of these isotopes can distinguish among fish originating from different farms. On the contrary, fatty acid and tissue proximate compositions and morphological parameters, which are useful in distinguishing between farmed and wild fish, are less informative in discriminating among fish originating from different farms.

Comparison of fatty acid composition of muscle, liver, mature oocytes, and diets of wild and captive Macquarie perch, Macquaria australasica, broodfish

Abstract Macquarie perch, an Australian native freshwater species, does not respond to hypophysation when caught from the wild, spawned and subsequently held in captivity. In this paper, the fatty acid composition of the liver, mature oocytes, muscle and diets of wild and tank-reared fish are compared. The fatty acid profiles of the two groups of fish were closely related to their diets, and of the fatty acid profiles, those of the liver showed the least variation between years. The most significant differences in the fatty acid profiles of the two groups were observed in the liver, in which tank-reared fish had more monoenes, largely 16:1 n − 7, but less n − 6 fatty acids and a higher n − 3 to n − 6 ratio than did wild fish. Muscle differed from other tissues in that 16:0 and 16:1 n − 7 acids were present in greater amounts than 22:6 n − 3 and did not show a consistent variation between wild and tank-reared fish. In the mature oocytes of wild fish polyunsaturated fatty acids were present in consistent amounts between years. The mature oocytes of tank-reared fish had lower levels of n − 6 fatty acids and as a result these oocytes had significantly higher n − 3 to n − 6 ratios compared with those of wild fish. Principal component analysis indicated that the fatty acid composition of all three tissues was clearly separable in the two groups of fish. It is hypothesised that the low levels of n − 6 fatty acids, in particular 20:4 n − 6, in the diet of tank-reared Macquarie perch, may be responsible for the lack of response to hypophysation techniques in these fish, owing to the lack of precursors for the synthesis of prostaglandins. It is also suggested that Macquarie perch, like its marine relatives, is incapable of de novo synthesis of the highly unsaturated fatty acids of the n − 3 and n − 6 series and has to rely on its diet for these fatty acids.

An evaluation of the suitability of selected waste products in feeds for three fish species

ABSTRACT Five types of aquatic food industry waste products (carp offal, carp roe, fish frames, trout offal and surimi processing waste) together with fish meal were evaluated for their suitability as potential fish meal replacements, partially or wholly, in diets for three species (rainbow trout, Murray cod and shortfin eel) cultured in Australia, using a number of criteria. The proximate composition of the ingredients on a dry matter basis including protein content, lipid and ash, varied considerably. The essential amino acid (EAA) contents of the waste products and fish meal decreased in the order: carp roe > fish meal > carp offal > ‘surimi’ processing waste > fish frames > trout offal. The results of cluster analysis of A/E ratios of waste products and fish whole body fell within three clusters. The EAAI of whole body tissue of Murray cod, rainbow trout and Australian shortfin eel however, were closest to fish meal, followed by fish frame waste and/or ‘surimi’ waste. The results on A/E ratios and EAAI did not conform to the raw data on TAA and EAA. Therefore, the study emphasizes the need to have a multi-prong approach to determine the suitability of ingredients for incorporation into fish feeds.

Physical characteristics, and proximate composition of oocytes, liver and muscle of wild caught and tank-reared Macquarie perch

Macquarie perch (Macquaria australasica) is a freshwater percichthyid endemic to south-eastern Australia. In view of its conservation status (indeterminate), and its importance as a sport fish, natural stocks are replenished through a breeding programme using mature stock taken from the wild each year.This paper is the first of a series of investigations instigated to understand the underlying causes of the lack of response of Macquarie perch, caught from the wild and spawned and then tankreared for a year, to hypophysation techniques. In this paper, results of physical characteristics, proximate composition and ovarian histology of wild-caught and tank-reared fish (injected with salmon GnRHa and non-injected) are presented. Oocyte diameter distribution patterns indicate that Macquarie perch spawn once each year, and that in tank-reared fish oocyte maturation is incomplete with only a small proportion of oocytes reaching maturation. The mean (sd) gonadosomatic and hepatosomatic indices of wild fish were 11.25 (2.38) and 0.59 (0.10) and that of tank-reared fish were 4.84 (0.70) and 1.44 (0.09) respectively. These two parameters differed significantly (p<0.05) in the two groups of fish.Major differences also existed in the proximate composition of the liver and the way the liver components responded to GnRHa injection. The percent (sd) protein, lipid and ash by dry weight in the liver of wild injected fish were 57.02 (0.66), 30.63 (1.22) and 8.24 (0.05) respectively while in the liver of tank-reared uninjected fish these values were 30.87 (1.36), 24.59 (1.18) and 6.43 (0.13) respectively. When expressed as an absolute amount or an amount kg−1 body weight, all of moisture, protein, lipid, ash and nitrogen free extract were greater in tank-reared than wild fish. No significant differences were observed between wild and tank-reared fish in the composition of the body musculature or the oocytes.

An evaluation of the use of the amphipod Austrochiltonia to control growth of Saprolegnia on the eggs of Murray cod Maccullochella peeli (Mitchell)

An experiment was undertaken to evaluate the use of the amphipod Austrochiltonia in controlling the growth of the fungus Saprolegnia on the eggs of Murray cod. The mean percentage survival of eggs and fry after 9 days was only 44.8% for Austrochiltonia-treated eggs. This value was not significantly different (P > 0.05) from that for groups of eggs in which no attempt was made to control fungal growth (57.3% survival), but was significantly less (P < 0.05) than that for groups of eggs from which dead and funguscovered eggs were hand-picked daily (76.5% survival).