Circumstances of energetic use of white muscle protein in two flatfish species, Hippoglossoides platessoides and Pleuronectes americanus: starvation, natural variation and reproductive demands on white muscle

Maddock, Dawn M. (1997) Circumstances of energetic use of white muscle protein in two flatfish species, Hippoglossoides platessoides and Pleuronectes americanus: starvation, natural variation and reproductive demands on white muscle. Masters thesis, Memorial University of Newfoundland.

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Abstract

White muscle moisture was examined in two species of flatfish indigenous to Newfoundland waters, the winter flounder (Pleuronectes americanus) and American plaice (Hippoglossoides platessoides), in relation to seasonal cycles and experimentally induced energetic stress. Natural elevation of white muscle moisture observed during the spawning season in H. platessoides reflects protein usage and is probably due, in part, to energetic demands imposed by batch spawning. The observation of developing yolky oocytes coinciding with evidence of recent spawning suggests the potential to increase fecundity during the spawning season by recruitment of immature oocytes for release in the current season. This might require further depletion of white muscle protein resulting in the significantly higher muscle hydrations observed at this time. -- Experimental conditions which imposed energetic stress on H. platessoides as a result of high temperatures caused restricted gonad development if condition of the fish was less than 0.85 prior to setup and allowed maintenance of low white muscle moisture. Low condition fish which underwent reproductive development despite unfavourable conditions, experienced high muscle hydration and resorption of vitellogenic oocytes was evident upon termination. Those fish with high condition prior to setup developed their oocytes to a mature, vitellogenic state and maintained significantly lower muscle moisture than low condition fish which were in similar state of reproductive development at termination. -- Depletion of white muscle protein is a reversible process. After only four months of refeeding, a rebound in condition and lowered white muscle moisture was observed in winter flounder, P. americanus, in which low condition and high white muscle moisture had been induced by starvation. The ability to selectively use and rebuild white muscle suggests an energetic storage system which has been developed to deal with energetic demands the fish might face in the wild, including reproductive development and dealing with food shortages. -- Glycerinated single fibre preparations were studied for contractile ability and sarcomere characteristics. Both H. platessoides and P. americanus have sarcomeres that are considerably shorter than those of mammalian tissue. Intrafibre sarcomere differences were also noted as sarcomeres near the insertion were shorter than those in the central fibre region. Comparisons between contractile ability of starved versus fed P. americanus were not quantitative since it was difficult to discern sarcomeres in fibres from starved fish. Contraction was observed in some fibres from starved flounder, probably the result of conservation of individual fibres or groups of fibres.

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