Genetic improvement of the Pacific oyster Crassostrea gigas (Thunberg) in Australia

The Pacific oyster industry in Australia is derived from importations from Japan in the late 1940s and early 1950s to Tasmania and is almost completely hatchery based. This makes it a good target for developing and deploying genetically improved strains. An allozyme survey comparing hatchery stocks with self‐recruiting Tasmanian stocks and with two collections from Japan found abundant variation and no significant evidence of allele loss. The subsequent selection programme (initiated in the summer of 1996/97) had several strands. We wanted to take advantage of the increased power that marker‐assisted selection could bring and, therefore, needed to develop a linkage map and isolate flanking markers around quantitative trait loci (QTLs). Several types of markers (allozymes, microsatellites and AFLPs) were used, and single‐pair crosses were set up; QTLs have been detected. Conventional selection programmes, one based on mass selection and one on family selection, have been established. Triploid Pacific oysters produced via chemical means have been available for several years, but rates of triploidy achieved by such means are usually less than 100%. In 1999, we will assess whether our tetraploid 2‐year‐old broodstock can be crossed with diploids to give 100% triploid offspring.     

Characterization of pig T cell growth factor and its species-restricted activity on human, mouse and sheep cells

Crude T cell growth factor was prepared from pig blood cells in mixed lymphocyte culture together with Concanavalin A. The TCGF was recovered from the crude supernatant by ammonium sulphate precipitation and fractionated by gel exclusion chromatography to yield active fractions corresponding to an apparent molecular weight of 23,000d. The TCGF was further purified by isoelectric focussing and was found to migrate as a single peak of pI 5 - 5.5. The crude preparation was found to support the growth of mouse and sheep activated cells but had no effect on human activated cells. Human TCGF supported the continued growth of activated pig cells whereas mouse and sheep TCGF had no such effect.     

Seawater transmission and infection dynamics of pilchard orthomyxovirus (POMV) in Atlantic salmon (Salmo salar)

The Tasmanian salmon industry had remained relatively free of major viral diseases until the emergence of pilchard orthomyxovirus (POMV). Originally isolated from wild pilchards, POMV is of concern to the industry as it can cause high mortality in farmed salmon (Salmo salar). Field observations suggest the virus can spread from pen to pen and between farms, but evidence of passive transmission in sea water was unclear. Our aim was to establish whether direct contact between infected and naïve fish was required for transmission, and to examine viral infection dynamics. Atlantic salmon post‐smolts were challenged with POMV by either direct exposure via cohabitation or indirect exposure via virus‐contaminated sea water. POMV was transmissible in sea water and direct contact between fish was not required for infection. Head kidney and heart presented the highest viral loads in early stages of infection. POMV survivors presented low viral loads in most tissues, but these remained relatively high in gills. A consistent feature was the infiltration of viral‐infected melanomacrophages in different tissues, suggesting an important role of these in the immune response to POMV. Understanding POMV transmission and host–pathogen interactions is key for the development of improved surveillance tools, transmission models and ultimately for disease prevention.     

Evaluation of sodium percarbonate as a bath treatment for amoebic gill disease in Atlantic salmon

Amoebic gill disease (AGD), caused by Neoparamoeba perurans, is a major health challenge for Atlantic salmon aquaculture globally. While freshwater bathing for 2 hr is effective in reducing infection severity, there is need for more rapid and lower cost alternatives. To this end, a combination of sodium percarbonate (SPC) in freshwater was examined for its treatment efficacy. Initial in vitro studies showed a reduction in amoeba viability when exposed for 30 min to freshwater containing >500 mg/L SPC. Subsequently, AGD‐affected salmon were bathed for 30 min in 16°C freshwater containing 100, 500 or 1,000 mg/L SPC, or for 2 hr in 16°C freshwater to mimic industry practice. Treatment at the highest SPC concentration caused extensive gill damage and substantial mortality. Neither occurred to a significant extent at lower SPC concentrations. Gill pathology of surviving fish 10 days post‐treatment (dpt) was comparable to or more severe than pre‐treatment, and significantly (p < .001) more severe than in 2 hr freshwater bathed fish. N. perurans DNA was confirmed by qPCR in all treatment groups at 10 dpt. The data indicate that a 30‐min exposure to SPC in freshwater is not a suitable alternative to existing freshwater treatment of AGD.     

Comparison of capsular opacification and refractive status after placement of three different intraocular lens implants following phacoemulsification and aspiration of cataracts in dogs

Objective  To evaluate the effect of lens design and biomaterial on formation of posterior capsular opacification (PCO) and refractive correction.
Animals studied  Sixty dogs undergoing bilateral phacoemulsification for mature or diabetic cataracts.
Procedures  One randomly selected eye received a rounded edge 41D polymethyl-methacrylate (PMMA) intraocular replacement lens (IOL) and the contralateral eye received either a squared edge 41D hydrophilic acrylic IOL ( n  = 35) or a squared edge 40D hydrophobic acrylic IOL ( n  = 25). At the (mean = 79 day) reexamination period, PCO was graded using direct slit-lamp observation and by masked observer evaluation of digital images of the IOLs. Streak retinoscopy and B-mode ultrasound were performed at this period.
Results  The PCO score via direct slit-lamp was significantly lower for the hydrophilic acrylic IOL when compared to the PMMA IOL. Masked observer evaluation of digital images revealed that the acrylic IOLs had lower but generally not statistically significant PCO scores than the PMMA IOLs. Streak retinoscopy showed that the PMMA IOL was significantly closer to emmetropia (+0.44 D) when compared to either the hydrophilic acrylic (+0.96 D) or the hydrophobic acrylic (+1.2 D) IOLs. B-mode ultrasonography revealed the center of the hydrophilic acrylic IOL is 0.31 mm closer to the retina and the center of the hydrophobic acrylic IOL is 0.63 mm further from the retina when compared to the center of the PMMA to retina distance.
Conclusions  Square edged foldable acrylic IOLs show a predisposition towards generating slightly less PCO than round edged PMMA IOLs in the early postoperative period, however, both acrylic IOLs had greater persistent hyperopia than the PMMA IOLs.