Vertebral fusions in farmed Chinook salmon (Oncorhynchus tshawytscha) in New Zealand.

Vertebral fusions are an established economic concern in farmed Atlantic salmon, but have not been studied in detail in farmed Chinook salmon. Two radiographic studies of vertebral fusions were performed in farmed Chinook salmon. Sixteen of 1,301 (1.2%) smolt and 201 of 2,636 (7.6%) harvest fish had fusions. There were no significant differences in the number of fused vertebrae/fusion in smolt compared with harvest fish. Secondly, tagged fish were repeatedly radiographed to determine the progression of the fusions. Nineteen (4.4%), 23 (5.3%) and 39 (9.0%) fish had fusions as smolt, after 129 days in sea water, and at harvest, respectively. There were no significant differences in the average number of vertebra/fusion between the three time points. Of the fusions that were observed in smolt, additional vertebra did not become fused in 81% of the lesions. Within the rare fusions that did progress due to the involvement of adjacent vertebra, an average of 1.6 vertebrae were added per year. Fish with fusions were significantly lighter than non-affected fish at harvest. Fusions are common in farmed Chinook salmon; however, they are typically stable after development. As fish with fusions were lighter at harvest, reducing fusions may have an economic benefit.

Temperature sensitive regions of the Chinook salmon vertebral column: Vestiges and meristic variation.

Variation of vertebral centra numbers is common in vertebrates. Likewise, the number of associated elements such as ribs and neural and haemal arches can vary and affect all regions of the vertebral column. In mammals, only the number of cervical vertebrae is invariable. Variation of total vertebral centra numbers is well documented in teleost fish, often related to temperature. Less information is available about which part of the vertebral column and which associated elements are liable to variation. Here, variation in number of vertebral centra and associated elements is studied in Chinook salmon in six distinct anatomical regions. Animals are raised at 8 and 12°C to ask whether the vertebral centrum numbers, the pattern, and the frequency of variation in particular regions are temperature dependent. No significant difference concerning the total number of vertebrae was found, but regional differences occurred between the 8 and 12°C groups. Twelve specimens out of 60 of the 12°C group had three postcranial vertebrae compared to only one specimen in the 8°C group. The number of transitional vertebrae is significantly different in 8 and 12°C specimens. Fewer transitional vertebrae occur in more anterior positions in 8°C specimens. Most specimens of both temperature groups had two ural centra; however 17 specimens out of 60 of the 12°C group had up to five ural centra. Specimens of the 12°C group show more variation in the presence of the vestigial ribs associated with transitional vertebrae. Clearly, the postcranial, transitional, and ural regions are temperature sensitive. This study shows that nonsignificant differences in the total number of vertebrae can mask significant regional variation. Variation of vertebral numbers could be the consequence of loss or gain of vertebral centra and/or a change in the identity of the associated element on the vertebral centrum.

Unilateral perivertebral fibrosis associated with lordosis, kyphosis and scoliosis (LKS) in farmed Chinook salmon in New Zealand.

Vertebral column lordosis, kyphosis and scoliosis (LKS) can result in downgrading of farmed Chinook salmon Oncorhynchus tshawytscha in New Zealand. No cause of LKS has been identified. Radiography and histology were used to quantify LKS and perivertebral fibrosis in 27 fish with LKS visible at harvest and 30 visually normal fish from 3 New Zealand farms. Radiographic LKS was present in all 27 fish with LKS and in 18 of 30 fish without visible LKS. Quantification of the radiographic severity revealed significantly higher radiographic severity scores in fish with visible LKS (mean ± SD = 5.89 ± 2.41) than in fish with no visible, but radiographic LKS (1.44 ± 0.86, p < 0.001). The most frequent histological finding was unilateral perivertebral fibrosis that often extended into the horizontal septum and adjacent myomeres resulting in separation or loss of myocytes. Fibrosis was visible in all fish with LKS and in 12 of 30 fish without visible LKS. Fibrosis scores were higher in fish with visible LKS (3.32 ± 1.71) than in fish without visible LKS (0.35 ± 0.57, p < 0.001). The radiographic LKS severity scores were significantly correlated to the fibrosis scores (R2 = 0.59 p < 0.001) in the fish. Histology of other tissues revealed multifocal inflammation within muscle, peripheral connective tissues and myocardium which were considered most likely incidental in these fish. In this study, LKS was consistently and significantly associated with perivertebral fibrosis, suggesting that perivertebral fibrosis is an important process in the development of LKS. Further research to determine the cause of the fibrosis is required.

Effects of temperature, epinephrine and Ca(2+) on the hearts of yellowfin tuna (Thunnus albacares).

Tuna are endothermic fish with high metabolic rates, cardiac outputs and aerobic capacities. While tuna warm their skeletal muscle, viscera, brain and eyes, their hearts remain near ambient temperature, raising the possibility that cardiac performance may limit their thermal niches. We used an in situ perfused heart preparation to investigate the effects of acute temperature change and the effects of epinephrine and extracellular Ca(2+) on cardiac function in yellowfin tuna (Thunnus albacares). Heart rate showed a strong temperature-dependence, ranging from 20 beats min(-1) at 10 degrees C to 109 beats min(-1) at 25 degrees C. Maximal stroke volume showed an inverse temperature-dependence, ranging from 1.4 ml kg(-1) at 15 degrees C to 0.9 ml kg(-1) at 25 degrees C. Maximal cardiac outputs were 27 ml kg(-1) min(-1) at 10 degrees C and 98 ml kg(-1) min(-1) at 25 degrees C. There were no significant effects of perfusate epinephrine concentrations between 1 and 100 nmol l(-1) at 20 degrees C. Increasing extracellular Ca(2+) concentration from 1.84 to 7.36 mmol l(-1) at 20 degrees C produced significant increases in maximal stroke volume, cardiac output and myocardial power output. These data demonstrate that changes in heart rate and stroke volume are involved in maintaining cardiac output during temperature changes in tuna and support the hypothesis that cardiac performance may limit the thermal niches of yellowfin tuna.