Spatial and non-spatial risk factors associated with cage-level distribution of infectious salmon anaemia at three Atlantic salmon, Salmo salar L., farms in Maine, USA

The distribution of infectious salmon anaemia (ISA) was examined among 80 cages from three Atlantic salmon grow-out farms in Maine, USA that were stocked with smolts from a single hatchery. Cage-level disease was broadly defined as one or more moribund fish testing positive for infectious salmon anaemia virus (ISAV) by RT-PCR and a second confirmatory test (IFAT, culture or genotype sequence). Spatio-temporal and cage-level risks were explored using logistic regression and survival analysis. Non-spatial risk factors associated with ISA, or shortened survival time to disease, included increased predation, trucking company choice for smolt transfers, a finely-sedimented benthic substrate, and smaller average size of smolts at stocking. Univariable analysis identified the time-dependent spatial factor 'adjacency to newly infected cages' to be predictive of new infection in neighbouring cages 11-12 weeks later. However, none of the spatial factors, or their lags retained relevance in multiple-variable models. The results suggest a diffuse distribution of virus exposure throughout infected sites, with host-susceptibility factors probably influencing disease manifestation in individual cages. The narrow focus of the current study may limit application of the findings to other sites and year-classes. However, these data support the relevance of husbandry efforts to optimize fish health in regions affected by ISAV.     

Promotion of pistillate flowering inCucurbita by 2-chloroethylphosphonic acid

Summary All accessions tested of four cultivated species ofCucurbita responded to seedling treatment with 250 ppm 2-chloroethylphosphonic acid by developing only pistillate flowers for an extended period. This growth regulator is a promising means of facilitating hybrid seed production of squash. A similar treatment did not induce flowering of wild species ofCucurbita that were vegetative under the environmental conditions of the experiment.Approved by the Director of the New York State Agricultural Experiment Station for publication as Journal Paper No. 1737.     

THE UTILIZATION OF GRASS FED INDOORS TO YOUNG BEEF CATTLE, WITH OR WITHOUT SUPPLEMENTARY BARLEY

An experiment was carried out in which grass was cut and fed indoors, with or without supplementary barley. Seven animals were allocated to each of the following treatments: (1) grass ad lib . without supplementary barley; (2) grass ad lib . with supplementary barley at the rate of 0.5 lb/100 lb bodyweight; (3) grass ad lib . with supplementary barley at the rate of 1 lb/100 lb bodyweight. Supplementary barley increased total dry-matter intake and improved daily liveweight gain and food conversion rate. The mean daily liveweight gains for the 17-week experimental period were 1.60, 1.91 and 2.20 lb and the corresponding feed dry-matter conversion ratios were 6.18, 5.67 and 5.55 for Treatments 1, 2 and 3, respectively.
The dry-matter digestibility of the diets was slightly higher when the grass was supplemented with barley than when grass alone was given. Although barley depressed the digestibility of protein, the absolute and the proportionate retention of nitrogen was increased. This was particularly marked on Treatment 3, presumably because of the higher net energy value of the diet containing the greater amount of barley. The N-retention data corresponded to the rates of liveweight gain obtained.     

Comparison of early life history stages of the bay scallop, Argopecten irradians: Effects of microalgal diets on growth and biochemical composition

The culture of bay scallops, Argopecten irradians, is limited by a reliable and affordable supply of spat and the ability to ensure that animals attain market size within a single growing season. The main goals of our study were thus: (1) to develop growth-optimizing algal diets for implementation in hatcheries, and (2) to identify and compare bay scallop postlarval and juvenile dietary requirements, especially of lipids and fatty acids, which if met may enhance production. Nutritional needs of postlarval bay scallops (present study) are compared with those of sea scallops, Placopecten magellanicus, offered the same diets in a previous companion study. To this end, postlarval (initial shell height, SH = 240 μm) and juvenile (initial SH = 10 mm) bay scallops were offered 6–7 microalgal diet combinations at 20 °C, for 3 weeks. A similar growth ranking among diets was observed between the two developmental stages. A combination diet of Pavlova sp. (CCMP 459) and Chaetoceros muelleri was far superior to any other diet tested, yielding growth rates of 58 and 357 μm day^− 1 which were 65% and 25% higher than the next highest performing diet of Tetraselmis striata/C. muelleri in postlarvae and juveniles, respectively. The T. striata/C. muelleri diet, which is limited in the n-3 fatty acid docosahexaenoic acid (DHA), yielded very poor growth of sea scallop postlarvae in a prior study, indicating that bay scallops may have less stringent requirements for DHA than sea scallops. The Pav 459/C. muelleri diet, which also supported the highest growth of sea scallop postlarvae, is characterized by elevated levels of the n-6 fatty acids, arachidonic (AA) in C. muelleri and 4,7,10,13,16-docosapentaenoic (DPA) in Pav 459. The two diets deficient in AA and n-6 DPA, Pavlova lutheri/Thalassiosira weissflogii and P. lutheri/Fragilaria familica, yielded the lowest growth rates in both bay scallop postlarvae and juveniles. Tissue enrichment of these two fatty acids relative to the diet, as well as overall enrichment in ∑n-6 fatty acids was observed across developmental stages and dietary treatments. A similar pattern has previously been observed in sea scallop postlarvae, suggesting a dietary requirement for n-6 fatty acids in pectinids that has often been overlooked in the past.     

Changes in thyroid hormone levels in eggs and larvae and in iodide uptake by eggs of coho and chinook salmon,Oncorhynchus kisutsch andO. tschawytscha

Developmental profiles of thyroxin (T₄), triiodothyronine (T₃) and radioactive iodide uptake were established for eggs and T₄ and T₃ profiles were established for larvae (whole-body, yolk-only and body-only) of coho and chinook salmon. T₄ and T₃ were consistently present in all samples. In eggs, hormone levels remained fairly constant in all cohorst for at least the first three weeks of incubation, but then fluctuated in both directions in some sample groups. Large increases in T₄ (from 9 ng/g to 245 ng/g) were seen in 1985 chinook eggs 28 days after fertilization. Radioactive iodide uptake (which was used as a possible indicator of thyroxinogenesis) increased at least 10-fold in both 1986 coho and chinook eggs from 23–30 days after fertilization. T₄ (62 ng/g) and T₃ (393 ng/g) were found in the bodies of 28-day-old 1986 chinook embryos. In whole larvae, hormone levels varied depending upon the cohort studied. In general, initial body-only concentrations of both T₄ and T₃ decreased as body weight increased, but before yolksac resorption was completed, both thyroid hormone content and concentration increased (except for chinook T₃). T₄ and T₃ content in larval yolk stayed constant as yolksac size decreased, resulting in increased thyroid hormone concentration in the yolksac. All of these data suggest that the initial source of thyroid hormones in coho and chinook salmon eggs is maternal, but that by approximately 3–4 weeks after fertilization, the developing embryos begin to produce their own thyroid hormones. After hatching, increases in tissue T₄ and T₃ concentration coupled with constant T₄ and T₃ content in diminishing yolksacs suggest that larvae also produce their own thyroid hormones; yolksac content then may reflect both the original maternal hormones and the larva-producted hormones.     

Expression of genes involved in the early immune response at the distal segment of the gut in Atlantic cod, Gadus morhua L. after vaccination with a bacterial antigen

The gastro-intestinal tract serves as the route of infection of most bacterial pathogens in fish, and the immune response genes in the gut produce substances that provide an initial defense during pathogen invasion. The expression of some genes involved in antibacterial defense, cell-mediated immunity and inflammation in the distal intestine of Atlantic cod, Gadus morhua L., was investigated following intraperitoneal vaccination with heat-killed Vibrio anguillarum. Tissue samples of the distal intestine were collected at 0, 1, 3, 7 and 10 days post-vaccination (dpv) and processed for semi-quantitative RT-PCR analyses. Expression of the bactericidal/permeability-increasing protein/lipopolysaccharide-binding protein (BPI/LBP), g-type lysozyme, non-specific cytotoxic cell receptor protein-1 (NCCRP-1) and interleukin-8 (IL-8) significantly increased during the early stages post-vaccination, that is, 1–3 dpv, followed by a decrease in their expression returning to their initial levels. Transferrin and apolipoprotein A-I, although weakly expressed in the distal intestine, also increased in the vaccinated fish. Interleukin-1β (IL-1β) was significantly decreased in its expression level relative to the PBS-injected fish at 3 and 7 dpv. The expression of these immune-related genes in the distal intestine as a result of vaccination provides valuable information on the mechanisms of gut immunity in the fish against pathogenic bacteria, particularly during the early stages of infection.     

Effects of varying dietary compositions using common feed ingredients on growth and feed efficiency of pond‐raised channel catfish Ictalurus punctatus (Rafinesque)

Two experiments were conducted to evaluate various ingredient combinations in a 28% or 32% protein diet for optimum performance of channel catfish Ictalurus punctatus. All diets contained soybean meal and corn, but with or without cottonseed meal, wheat middlings or fish meal (FM). Channel catfish fingerlings were stocked into 0.04 ha earthen ponds at 18 530 fish ha^?1. Fish were fed one of eight diets once daily to apparent satiation for two growing seasons. Results demonstrated that the dietary ingredient composition used had significant effects on fish performance, but magnitude of differences was relatively small. Overall, diets containing FM resulted in greater weight gain (Experiments 1 and 2) and lower feed conversion ratio (Experiment 1) than fish fed all‐plant diets. However, certain combinations of plant ingredients provided the similar fish growth as some diets containing FM. There were no significant differences in weight gain between fish fed soybean meal–corn or soybean meal–corn–wheat middlings‐based diets with cottonseed meal or FM. The use of wheat middlings in the diet had no significant effects on fish production characteristics.