Farm-raised shrimp: good aquacultural practices for product quality and safety

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Witcherwell hatchery husbandry regime

Witcherwell like most new hatcheries has gone through a honeymoon period during which no major fish health problems have occurred. However, in 1994, there was an outbreak of Bacterial Gill Disease which caused high mortalities. This has emphasised the importance of developing and maintaining optimum husbandry practices for Witcherwell. These may also be applicable to other fish culture units in Central Area and the NW. To avoid the reoccurence of bacterial gill disease or other health problems and to ensure that stock of good health and quality are produced good husbandry practices must be followed. This report inculdes information on stock, disinfection, cross-contamination, cleaning, feed rates, flow rates, screening, treatments and possible problems.

Staging ovaries of Haddock (Melanogrammus aeglefinus): implications for maturity indices and field sampling practices

We build on recent efforts to standardize maturation staging methods through the development of a field-proof macroscopic ovarian maturity index for Haddock (Melanogrammus aeglefinus) for studies on diel spawning periodicity. A comparison of field and histological observations helped us to improve the field index and methods, and provided useful insight into the reproductive biology of Haddock and other boreal determinate fecundity species. We found reasonable agreement between field and histological methods, except for the regressing and regenerating stages (however, differentiation of these 2 stages is the least important distinction for determination of maturity or reproductive dynamics). The staging of developing ovaries was problematic for both methods partly because of asynchronous oocyte hydration during the early stage of oocyte maturation. Although staging on the basis of histology in a laboratory is generally more accurate than macroscopic staging methods in the field, we found that field observations can uncover errors in laboratory staging that result from bias in sampling unrepresentative portions of ovaries. For 2 specimens, immature ovaries observed during histological examination were incorrectly assigned as regenerating during macroscopic staging. This type of error can lead to miscalculation of length at maturity and of spawning stock biomass, metrics that are used to characterize the state of a fish population. The revised field index includes 3 new macroscopic stages that represent final oocyte maturation in a batch of oocytes and were found to be reliable for staging spawning readiness in the field. The index was found to be suitable for studies of diel spawning periodicity and conforms to recent standardization guidelines.