Impact of dietary phosphorous in diploid and triploid Atlantic salmon (Salmo salar L.) with reference to early skeletal development in freshwater.

In order to assess the effect of dietary phosphorus (P) in reducing vertebral malformations and improving freshwater (FW) performance in triploid Atlantic salmon (Salmo salar), both triploid and diploid Atlantic salmon were fed three different dietary P inclusion levels (low: 4.9, medium: 7.7, and high: 9.7 g available P kg-1) from first feeding until smolt. Somatic and skeletal response was assessed at fry (~0.5 g), parr (~5 g) and smolt (~45 g) stages. Triploid parr initially grew faster on the high P diet, while groups fed low P resulted in a significantly higher weight at smolt. Image analysis of double stained Alcian blue and Alizarin red S fry revealed that low P fed triploid fish presented less well mineralised vertebrae, and significantly more malformed vertebrae in both parr and smolt stages following x-ray radiographic assessment. Triploid parr fed high and medium P had similar numbers of malformed vertebrae relative to their diploid counterparts but greater numbers than at smolt. Low P fed triploids had the highest prevalence of jaw and vertebral malformations as well as the highest number of deformed vertebrae in the central caudal vertebral region, which was more pronounced at parr than at smolt. Shorter vertebrae dorso-ventral lengths were observed throughout the spinal column (R1-R4) in parr fed low P and only in the caudal region (R3) at smolt. In parr, both ploidies showed reduced phosphate homeostasis protein fgf23 gene expression in vertebrae when fed low P diets, while triploids showed greater down-regulation of osteogenic factors (alp, opn and igf1r) between diets relative to diploids, suggesting possible greater active suppression of mineralisation and reduced osteogenic potential in triploids. No effects of diet or ploidy on gene expression were evident at smolt. Comparisons between development stages suggest early P supplementation in triploids is crucial for skeletal development. Ultimately, reducing vertebral deformities observed at smolt with higher P supplementation in triploids could contribute towards improving skeletal performance and welfare of the stocks in the marine phase.

Further observations of the ovarian response of the tammar wallaby (Macropus eugenii) to exogenous gonadotrophins: an improved method for superovulation using FSH/LH.

This study reports the development of an improved superovulation protocol in the monovulatory tammar wallaby, Macropus eugenii. Treatment with pregnant mare's serum gonadotrophin (PMSG; 10-20 IU) inhibited follicle development in the corpus luteum (CL)-bearing ovary and only 2-3 eggs per female could be recovered after ovulation induction with gonadotrophin releasing hormone (GnRH; 3 x 30 microg at 3-h intervals) or porcine luteinizing hormone (LH; 4, 5 or 8 mg) 3 days after PMSG priming. Treatment with porcine FSH (8 x 6 mg at 12-h intervals for four consecutive days) was found to override this inhibition and resulted in the recovery of 7-13 eggs per female after ovulation induction with porcine LH (4 mg on day 5). For these animals, there was no difference in numbers of developing follicles, ovulation sites and eggs recovered between the CL- and non-CL-bearing ovaries. This FSH/LH protocol was effective in both cycling and non-cycling females, and multiple ovulation occurred from about 36 h after LH treatment. After LH treatment, eggs were recovered from the oviduct at 36-50 h. At 51-57 h, 12-25% of eggs were recovered from the uterus, and by 75 h all eggs were recovered from the uterus. It is concluded that the described FSH/LH protocol used results in higher ovulation success than the PMSG/GnRH method.