Production, disinfection and evaluation for aquaculture applications of rotifer resting eggs from Bohai Bay, P.R. of China

The dynamics of resting egg production of the rotifer Brachionus plicatilis originating from a wild population in the Tanggu Saltworks (P.R. China) was investigated. In the natural environment as well as in semi-controlled rearing conditions an increased resting egg production was noticed with declining food availability. Processed resting eggs had a hatching efficiency of 3 x 10 6 rotifers per gramme irrespective of their origin. Hatching started 22 h after the initiation of incubation and was completed after 36 h. Rotifers obtained from resting eggs could be further cultured on Culture Selco® and enriched with Super Selco®. The fatty acid profile of these rotifers were not divergent from reference rotifers (originating from the Laboratory of Aquaculture and Artemia Reference Centre) demonstrating that this strain was not catabolizing essential fatty acids and could be used for enrichment purposes. Storage of resting eggs at 4°C resulted in a 50% lower hatching after 1 year but remained stable during the next 2 years. The resting eggs used for storage could easily be disinfected without affecting their hatching characteristics. These results indicate that this material could be used as inocula for mass cultures of live food for commercial hatcheries.     

Possible applications of modern fish larviculture technology to ornamental fish production

There has been rapid development in the marine foodfishlarviculture technology in Europe since the early eighties,especially in the flat fish, turbot and halibut, and the bass andbream species. The most significant improvements in the eightieswere the introduction of light control, artificial reproductiontechniques, appropriate water treatment and the use of rotifersand Artemia nauplii of specific sizes and in the late eightiesand early nineties the quality enhancement of live food organismsusing specific enrichment techniques. Present research is focusedon the implementation of several microbial techniques to improvethe hygiene of live prey and fish.Many of the modern larviculture techniques being used in marine foodfish could be adapted for application in the ornamental fish industry. For examples, research in the Onamental Fish Section, Primary Production Department, Singapore has demonstrated that the use of freshwater rotifers and Artemia nauplii would enable artificial rearing of Discus in the absence of the parent fish and improve the larval performance of Gouramis and Tetra larvae. The use of such small live food organisms is likely to facilitate breeding of new fish species with small larvae. Research has also indicated that the use of diets containing vitamin C and certain immuno-stimulants improved the stress resistance of guppy. Such techniques would have important application in the fish transport, an important aspect in the ornamental fish industry     

Effect of number of meals and frequency of feeding on voluntary feed intake of Colossoma macropomum (Cuvier)

Juvenile, 0.87 g Colossoma macropomum (Cuvier) were submitted to different ad libitum feeding regimes. Feeding frequency ranged from one to five meals per day and intervals between meals from 3 h to 24 h. Higher feeding frequencies resulted in higher feed uptake, a higher growth rate and a decreased feed utilization efficiency. Feed consumption was lower at 0700 h than at 1900 h. The amount of feed from different meals persisting in the digestive tract was determined with chromic-oxide-marked feed. This method revealed that with ad libitum feeding, about 21% of the feed remained uneaten. Feed losses did not differ significantly between feeding regimes. Feed accumulated in the digestive tract in the morning and early afternoon. In the late afternoon most feed rests disappeared from the digestive tract and feed consumption increased. It is suggested that feed uptake and growth of C. macropomum can be improved by extending the feeding period after 1900 h.     

Resistance to Streptococcus iniae and its genetic associations with traits of economic importance in Asian seabass (Lates calcarifer)

Streptococcus iniae is one of the most serious aquatic pathogens, causing significant economic losses in marine and freshwater species, including Asian seabass (Lates calcarifer). Controlling this gram‐positive bacterial pathogen has been an issue in aquaculture systems, due to the combined effects of aquaculture intensification and climatic impacts. To date, there have not been any genetic parameter estimates for S. iniae resistance in Asian seabass. The main aim of this study was to examine genetic variation in S. iniae resistance and its genetic correlations with growth and cannibalism in Asian seabass families produced from a breeding programme for high growth in 2016 and 2017. The study included a total of 5,835 individual fish that were offspring of 41 sires and 60 dams (31 half‐sib and 34 full‐sib families). The experimental fish were challenged by intraperitoneal injection with a volume containing 10⁵ CFU (colony‐forming unit)/fish. Resistance to S. iniae was measured as survival rate at 6 hr, 3, 5, 7, 10 and 15 days post‐challenge test. There were significant variations in S. iniae resistance among families at different observation periods (ranging from 24.4% to 80%). Restricted maximum‐likelihood method and mixed model analysis were applied to estimate heritability for S. iniae resistance. The heritability for S. iniae resistance ranged from 7% to 18% across different statistical models used. The common full‐sib effects accounted for 0.1%–2% of the total variation in resistance to S. iniae. Genetic correlations of the S. iniae resistance at 6 hr and 3 days with later post‐challenge test periods were low to moderate. However, these estimates for S. iniae resistance between successive measurement times (5, 7, 10 and 15 days) were high and close to 1. The genetic correlations of resistance with body weights at 180, 270 and 360 days post‐hatch were not significant as well with cannibalism. It is concluded that there is substantial additive genetic variation in resistance to S. iniae, suggesting there is potential for genetic improvement of Asian seabass for resistance to S. iniae through selective breeding.     

Vaccine-induced protective immunity against Aeromonas salmonicida tested in experimental carp erythrodermatitis

Abstract The development and applicability of a dose-controlled experimental infection with atypical Aeromonas salmonicida in carp is described. The proliferation and clinical manifestations of experimentally induced carp erythrodermatitis mimicked a natural infection. An in-vivo assay was used to evaluate the lethal properties of cell-free culture supernatants and a simple serum-free growth medium was devised for maintaining the virulence of the challenge strain. Depending on the inoculation dose, a sublethal (chronic) to a lethal (acute) infection could be induced, and a dose-response relation was observed between A. salmonicida inoculum size and carp mortality. The dose-controlled experimental infection was used as a challenge test for laboratory evaluation of the efficacy of potential vaccine candidates. The vaccine candidates tested, a cell envelope preparation, purified lipopolysaccharide and purified A-layer (ACE) protein showed no protection or only a feeble one at the best, while formalinized whole cells showed a consistent but only moderate protection. In contrast, when concentrated, detoxified culture supernatant was used, the carp were protected against a subsequent lethal challenge. These observations indicate that immunity against A. salmonicida extracellular products is of prime importance.     

AN INFECTED HIP PROSTHESIS IN A DOG DIAGNOSED WITH A 99mTC-CIPROFLOXACIN (INFECTON) SCAN

This case report describes the use of the 99mTc-labeled radiopharmaceutical ciprofloxacin (Infecton) in a case of hip prosthesis loosening in a dog. Serial planar radiographs were not conclusive, and culture of the synovial fluid was negative. Antibiotic treatment did not result in improvement of the lameness. Scintigraphy was performed with 99-Tc-Infecton, a tracer claimed to be specific for infection. Antibiotic treatment was interrupted 6 weeks prior to the examination. Planar and tomographic images at 3 h and at 24 h postinjection showed increased activity along the acetabulum and the proximal femoral bone surrounding the femoral prosthesis, indicating focal infection. Bacteriology performed after removal of the implant revealed Pseudomonas aeruginosa.     

Virulence of South African isolates of Haemophilus paragallinarum. Part 3: experimentally produced NAD-independent isolate

A NAD-dependent isolate 46 (C-3) of Haemophilus paragallinarum, which was previously demonstrated to be of high virulence, was transformed to NAD independence using a plasmid isolated from a naturally occurring NAD-independent isolate of H. paragallinarum. The transformation was performed by two different methods and the identity of all of the isolates, before and after transformation was confirmed using a H. paragallinarum-specific PCR test. The transformed NAD-independent serovar C-3 isolate and the wild-type serovar C-3 isolate were used to experimentally infect vaccinated layer chickens. It was shown that the transformation to NAD independence significantly altered the virulence of the serovar C-3 isolate that was used in the transformation experiment. The mechanisms responsible for a decrease in virulence are not clear, but may be related to the pathology of the transformed isolate in the sinus of the chickens.     

Proteoglycans from the vertebral cartilage of the clearnose skate,Raja eglanteria: Inhibition of hydroxyapatite formation

Studies were undertaken to examine the importance of organic proteoglycan matrices in the calcification of elasmobranch vertebral cartilage. Proteoglycans were extracted from the vertebral cartilage of the clearnose skate, Raja eglanteria Bosc, with a 3M guanidine hydrochloride/10% EDTA solution. Proteoglycan solutions (12 g ml^–1) were effective inhibitors of hydroxyapatite formation in vitro from high concentration calcium phosphate solutions. Inhibition of crystal formation appears to occur through the restriction of phase transformation from a calcium phosphate precursor to hydroxyapatite crystals. The concentration and/or degradation of proteoglycans in elasmobranch vertebral cartilage may have a physiological role in the production of alternating mineral-rich and mineral-poor growth zones, currently used in ageing studies.     

Differences between the ovine tonsils based on an immunohistochemical quantification of the lymphocyte subpopulations

In sheep, the pharyngeal first defence line against oral and inhaled antigens is organized in six tonsils. Since tonsils are regarded as secondary lymphoid tissue and part of the acquired immune system which is subjected to induction through contact with antigens, an evaluation of the different lymphocyte populations in tonsils is useful to determine a tendency of the specific tonsils to more inductive or more effective immunity. By means of immunohistochemistry, different lymphocyte populations were quantified and localized using a panel of eight antibodies, i.e. anti-CD45, anti-CD21, anti-CD2, anti-CD3, anti-CD4, anti-CD8, anti-WC1 and anti-Ki67. The CD21+ B lymphocytes were localized within the tonsillar lymphoid follicles. The CD2+/CD3+ T lymphocytes were numerous in the interfollicular regions and were aligned underneath and within the epithelium but were also observed at the CD21+ pole of the lymphoid follicles. Near the lingual and tubal tonsils, and the tonsil of the soft palate, the CD45+ cells around the seromucous glands and in the lamina propria were mainly CD3+ T cells. In all tonsils, the WC1+ gamma delta T cells formed a small lymphocyte population which harboured the lamina propria and the interfollicular region. The relative percentages of the different lymphocyte populations of the large palatine and pharyngeal tonsils, which are macroscopically the most developed, were comparable. In contrast, the lingual tonsil was significantly different from the other tonsils not only by its small size and lack of lymphoid follicles, but also by the lymphocyte populations. Based on the lymphocyte populations, the ovine tonsils can be divided in three groups with the tonsil of the soft palate, the tubal and paraepiglottic tonsil forming an intermediate between the palatine and pharyngeal tonsils as true tonsils on the one side, and the lingual tonsil as a scattered lymphocyte aggregation on the other side.