Asian carp farming systems: towards a typology and increased resource use efficiency

Resource use efficiency in Asian carp farming systems is analysed based on a survey of 2493 farms of nine countries. Multivariate classification of farms by intensity and diversity identified six farm types: four types of specialized aquaculture farms at different levels of intensity, and two types of integrated agriculture–aquaculture systems. Pond‐based, specialized semi‐extensive systems (using mainly inorganic fertilizers and feeds of off‐farm origin), and integrated semi‐intensive systems (using feeds and fertilizer of both on and off‐farm origin) are by far the most common types, accounting for 59% and 27% of all farms respectively. Specialized semi‐extensive systems also show the highest protein and nutrient (N and P) use efficiencies, and among the highest labour use efficiency. Super‐intensive cage farms are less efficient in nutrient and labour use, but provide very high returns to land and capital investment. On average, the aquaculture components of integrated agriculture– aquaculture systems are less nutrient, land, and labour efficient than specialized semi‐extensive systems. Integrated semi‐extensive systems (using organic fertilizers of on‐farm origin) are particularly inefficient across all indicators. Hence in practice, gains in overall resource use efficiency through on‐farm integration with agricultural production are constrained by the relative inefficiency of the aquaculture subsystems on integrated farms. Although such systems can likely be improved, integration as such is not a panacea to increasing resource use efficiency. Wide variation in resource use efficiency within all systems indicates potential for substantial efficiency gains through improved management regardless of the fundamental choice of system.     

Experimental induction of mouthrot in Atlantic salmon smolts using Tenacibaculum maritimum from Western Canada

Mouthrot, or bacterial stomatitis, is a disease which mainly affects farmed Atlantic salmon, (Salmo salar, L.), smolts recently transferred into salt water in both British Columbia (BC), Canada, and Washington State, USA. It is a significant fish welfare issue which results in economic losses due to mortality and antibiotic treatments. The associated pathogen is Tenacibaculum maritimum, a bacterium which causes significant losses in many species of farmed fish worldwide. This bacterium has not been proven to be the causative agent of mouthrot in BC despite being isolated from affected Atlantic salmon. In this study, challenge experiments were performed to determine whether mouthrot could be induced with T. maritimum isolates collected from outbreaks in Western Canada and to attempt to develop a bath challenge model. A secondary objective was to use this model to test inactivated whole‐cell vaccines for T. maritimum in Atlantic salmon smolts. This study shows that T. maritimum is the causative agent of mouthrot and that the bacteria can readily transfer horizontally within the population. Although the whole‐cell oil‐adjuvanted vaccines produced an antibody response that was partially cross‐reactive with several of the T. maritimum isolates, the vaccines did not protect the fish under the study's conditions.     

Precommercial thinning as a silvicultural option for treating very dense conifer stands

Lack of available workforce in motor-manual operations has led to increased interest in mechanized precommercial thinning (PCT) treatments. We evaluated 15 years of growth and yield development of a very dense (27,000 stems ha^–1) balsam fir (Abies balsamea (L.) Mill) and black spruce (Picea mariana (Mill.) B.S.P.) stand after six PCT treatments: (1) motor-manual (MAN), (2) motor-manual with crop tree release (MAN-C), (3) mechanized (MEC), (4) mechanized with residual patches (MEC-P), (5) semi-mechanized (mechanized followed by motor-manual, MEC-S), and (6) unthinned control (CON). Compared to CON, both MAN and MEC-S increased height of balsam fir study trees by 53–56% and diameter at breast height (DBH) by 57–58%. MAN-C and MEC-S increased DBH of black spruce study trees by 15–31% over all other treatments. The proportion of merchantable basal area (BA) was higher in MAN (62%) and MEC-S (56%) than in CON (22%) and MEC (25%), without a reduction in total BA. PCT treatments that provided a uniform distribution of potential crop trees (MAN, MEC-S) performed better than MAN-C and MEC-P, while MEC yielded the poorest responses. Our findings highlight the need to develop new tailored mechanized systems for high wood production and low operational cost.     

Experimentally evolved populations of the potato cyst nematode Globodera pallida allow the targeting of genomic footprints of selection due to host adaptation

In the current agronomical context of pesticide use reduction, deciphering the genetic bases of pathogen adaptation to plant defences is of major importance to improve durability of resistance. Indeed, knowledge of virulence gene frequencies in pathogen populations could allow the prediction of resistance durability before deployment. Globodera pallida is a major pest of potato crops for which a promising resistance QTL, GpaV_vrn, has been identified in Solanum vernei. An experimental evolution study, in which G. pallida lineages evolved on resistant or susceptible potato genotypes for up to eight generations, previously showed that G. pallida was able to rapidly overcome GpaV_vrn resistance. However, it was not known if enough genetic mixing occurred in these lineages to be able to detect islands of differentiation in a genome scan approach. Here, this question was investigated using 53 polymorphic microsatellite markers distributed along the genome and three different tests based on genetic differentiation and heterozygosity. Eight outlier loci were identified, indicative of genomic regions putatively involved in host adaptation. Several loci were identified by multiple detection methods and/or in two independent adapted lineages. Some candidate genomic regions identified also seemed to be involved in overcoming resistance to nematodes in a plant genotype harbouring the same resistance QTL in a different genetic background. These results validate the feasibility of a genome scan approach on biological material coming from short experimental evolution, and encourage the use of a high coverage genome scan by whole genome resequencing.     

Scanning electron microscopic description of cellular activity and mineral changes in feline odontoclastic resorptive lesions

The cellular activity and changes in mineral composition of dental tissues involved in feline odontoclastic resorptive lesions were investigated. Teeth with at least 1 lesion (n = 10) were extracted from 10 different cats that were presented primarily for chronic gingivostomatitis and/or severe periodontal disease. Scanning electron microscopic methods were used to determine the presence of resorptive cells in 8 teeth while 2 teeth were evaluated for pathologic changes in dental mineral composition. Observations were complicated by the presence of organic wear on the dental surfaces, however resorptive cells could be clearly identified in feline odontoclastic resorptive lesions. Resorptive cells had morphologic features indicative of "osteoclast-like" cells or odontoclasts. Resorptive cell activity created a resorption area of darker dentin continuous with physiologic dentin. The darker dentin area seemed poorly mineralized and showed a significantly lower calcium/phosphorous ratio compared with adjacent physiologic denting in 1 tooth. A significantly higher level of magnesium combined with available carbonate ions may have increased the solubility in areas of darker dentin.     

The immunophenotype of peripheral blood lymphocytes in clinically healthy dogs and dogs with lymphoma in remission

Lymphoma is a common cancer of dogs that frequently is treated with chemotherapy or radiation therapy. Response to therapy is variable and currently available diagnostic tests do not reliably predict response to therapy. Treatment for lymphoma often results in lymphopenia, but it is unknown whether the changes in circulating lymphocytes result from generalized or specific reduction of lymphocytes. In this study, blood lymphocytes from 12 clinically healthy dogs, 10 dogs in remission because of treatment for B-cell lymphoma, and 8 dogs in remission from T-cell lymphoma were analyzed by flow cytometry by using a panel of 20 antibodies reactive with canine leukocyte antigens. Results identified similar lymphocyte parameters in treated dogs regardless of the type of lymphoma. Treated dogs had >50% reduction in blood lymphocyte concentration, and an absolute decrease in most subsets of lymphocytes. Both groups of treated dogs had relative increases in the proportion of CD3+, T-cell receptor (TCR)αβ+, and CD90+ lymphocytes, and a decreased proportion of CD45RA+ cells. In addition, dogs with T-cell lymphoma in remission had a significant increase in the proportion of CD49d+ lymphocytes. These findings were interpreted as representing likely suppression of lymphocyte regeneration by chemotherapy, with a relative increase in the proportion of memory over naïve lymphocytes. Lack of correlation with the T- or B-cell origin of the initial lymphoma suggested that, by using flow cytometric methods, residual circulating neoplastic cells could not be detected. However, the changes in the lymphocyte profile of dogs treated with chemotherapy may have relevance to their immunocompetence.     

Plasma hormones and metabolites in cattle in relation to breed (Belgian Blue vs Holstein) and conformation (double-muscled vs dual-purpose type)

Four Belgian Blue double-muscled type (BBDM) bulls, four Belgian Blue dual-purpose type (BBDP) bulls and four Holstein bulls were used in a fattening trial in order to relate differences in the extent of muscle development and adiposity to differences in digestibility, endocrine status, protein and lipid metabolism. The larger muscle development in BBDM animals was associated with a trend to higher nitrogen retention, higher food conversion efficiency (p<0.05) and lower apparent digestibility (p<0.05). No difference was found between the groups for plasma glucose concentration. Higher creatinine, lower -amino nitrogen, lower triglycerides and higher non-esterified fatty acid plasma levels were observed in BBDM as compared to Holstein bulls (p<0.05), the BBDP group being intermediate. A trend to a higher cholesterol plasma level was found in BBDM animals. There was no difference between the three groups in plasma fatty acid composition, except for the C_14:0 content. Some of the differences in plasma metabolites were related to carcass composition and endocrine regulation, a decrease in muscle development and an increase in adiposity being associated with lower growth hormone production (p<0.05) and higher insulin (p<0.05) and IGF₁ secretions. The insulin/growth hormone ratio at the end of the fattening period was 0.0011, 0.0018 and 0.0069 in BBDM, BBDP and Holstein bulls, respectively, and was directly associated with fat deposition.Abbreviations BBDM Belgian Blue breed double-muscled type - BBDP Belgian Blue breed dual-purpose type - IGF₁ insulin-like growth factor 1 - NEFA non-esterified fatty acids - T₃ triiodothyronin - T₄ tetraiodothyronin     

Accounting for spatial autocorrelation improves the estimation of climate,physical environment and vegetation’s effects on boreal forest’s burn rates

Context

Wildfires play a crucial role in maintaining ecological and societal functions of North American boreal forests. Because of their contagious way of spreading, using statistical methods dealing with spatial autocorrelation has become a major challenge in fire studies analyzing how environmental factors affect their spatial variability.

Objectives

We aimed to demonstrate the performance of a spatially explicit method accounting for spatial autocorrelation in burn rates modelling, and to use this method to determine the relative contribution of climate, physical environment and vegetation to the spatial variability of burn rates between 1972 and 2015.

Methods

Using a 482,000 km² territory located in the coniferous boreal forest of eastern Canada, we built and compared burn rates models with and without accounting for spatial autocorrelation. The relative contribution of climate, physical environment and vegetation to the burn rates variability was identified with variance partitioning.

Results

Accounting for spatial autocorrelation improved the models’ performance by a factor of 1.5. Our method allowed the unadulterated extraction of the contribution of climate, physical environment and vegetation to the spatial variability of burn rates. This contribution was similar for the three groups of factors. The spatial autocorrelation extent was linked to the fire size distribution.

Conclusions

Accounting for spatial autocorrelation can highly improve models and avoids biased results and misinterpretation. Considering climate, physical environment and vegetation altogether is essential, especially when attempting to predict future area burned. In addition to the direct effect of climate, changes in vegetation could have important impacts on future burn rates.

     

Availability of standing trees for large cavity-nesting birds in the eastern boreal forest of Québec,Canada

Large cavity-nesting birds depend on large-diameter trees for suitable nest sites. The increased spatial extent of commercial timber harvesting is modifying forest structure across the land base and may thus compromise the availability of large trees at the landscape scale. In this study, our objectives were to (1) characterize the availability of large living and dead trees in old-growth stands dominated by different tree species and surficial deposits that encompass the range of natural cover types of eastern Québec's boreal forest; (2) analyze the distribution of trees among decay-classes; and (3) compare the availability of large trees in unharvested, remnant, and harvested stands for the entire range of decay-classes. A total of 116 line transects were distributed across unharvested forests, remnant linear forests, and cutblocks in cutover areas. Unharvested forest stands (black spruce [Picea mariana], balsam fir [Abies balsamea]–black spruce, balsam fir–white spruce [Picea glauca] and balsam fir) reflected a gradient of balsam fir dominance. The remnant forests selected were isolated for 5–15 years. Analyses were performed at two diameter cut-off values. Trees with DBH ≥20 cm were considered for availability of total trees whereas trees with DBH ≥30 cm were considered for availability of large trees. Forest stands comprised high proportions of standing dead trees (33% of all stems, 8% were large dead stems). Availability of total and large standing trees increased with the dominance of balsam fir in stands. Forest stands located on thick surficial deposits showed higher densities of large dead trees for every stand type suggesting a higher productivity on those sites. Availability of stems according to decay-classes showed a dome-shaped distribution with higher densities of snags in intermediate decay stages. However, for large stems, black spruce stands showed a significantly lower availability that was consistent across all decay-classes. In linear remnant forests, pure balsam fir stands were absent. Remnant stands thus showed a much lower availability in large trees when compared with unharvested balsam fir stands. Clearcuts had the lowest densities of dead trees across sampled stands. Current even-aged management practices clearly affect availability and recruitment of large trees, therefore forest-dwelling wildlife relying on these structures for breeding is likely to be affected by large-scale harvesting in coniferous boreal forests.