Characterisation of 'swollen yolk-sac syndrome' in the Australian freshwater fish Murray cod, Maccullochella peelii peelii, and associated nutritional implications for large scale aquaculture
Rm. Gunasekera et al., Characterisation of 'swollen yolk-sac syndrome' in the Australian freshwater fish Murray cod, Maccullochella peelii peelii, and associated nutritional implications for large scale aquaculture, AQUACULTURE, 169(1-2), 1998, pp. 69-85
The Murray cod is artificially propagated by harvesting naturally spawned!
fertilised eggs laid in nest boxes by captive, pond-reared broodfish, in mi
d to late southern spring and early summer. From 1988-1993, a condition ref
erred to as 'swollen yolk-sac syndrome' (SYSS) accounted for increasingly s
ignificant mortalities of Murray cod eggs and newly hatched larvae, often r
esulting in total mortality of eggs and larvae during incubation and larval
rearing stages. SYSS appears to be similar to the well known 'blue-sac dis
ease' (BSD) in salmonids but without the 'bluish tinge' coloration of the s
erous fluid in the yolk-sac attributed to BSD. Early investigations ruled o
ut that SYSS condition was caused by a pathogen, viral, bacterial or a para
sitic protozoan, and this led to the subsequent investigations on the possi
ble nutritionally related causes of the syndrome, which are reported here.
The eggs of normal and SYSS spawns differed in many respects; the latter we
re lighter and had less moisture (P < 0.05), but did not differ in the amou
nt of protein and/or lipid content per egg. The free amino acid (FAA) conte
nt of the two types of eggs were different however, when all the essential
amino acids (EAA) and non-essential amino acids (NEAA) of the FAA pool were
found in significantly lower amounts (nmol/egg) in SYSS eggs (EAA-11.84 +/
- 0.0.90; NEAA-10.68 +/- 0.66) compared to normal eggs (EAA-21.67 +/- 1.M;
NEAA-16.64 +/- 1.26). On the other hand, the differences in the total amino
acid (TAA = protein bound + free) content and the fatty acid content of th
e egg types were relatively minor. It was also observed that broodstock, th
e spawns of which manifested SYSS, when allowed to forage in a relatively l
arge pond, with ample natural food sources, for a period of time, their sub
sequent spawns tended to be normal. In eggs and larvae of spawns of such re
habilitated females, the amount of individual amino acids of the FAA pool w
as intermediate to that of normal and SYSS. All evidence appears to indicat
e that the SYSS syndrome in Murray cod is related to broodstock nutrition,
possibly a result of cumulative effects of dietary deficiencies over time.
(C) 1998 Elsevier Science B.V. All rights reserved.