A more detailed understanding of the immune mechanisms involved in anti-inflammatory events in fish is required for effective disease control in aquaculture. Significant expansion of immune genes, often resulting from whole genome duplication events in teleost fish, adds complexity to their potentially anti-inflammatory pathways. This thesis contributes to a more complete insight into the suppressor of cytokine signalling (SOCS) and transforming growth factor-β1 (TGF-β1) gene system in fish by the discovery of paralogues and reporting of ways in which these potential negative regulators of immune responses can be induced in the the commercially valuable rainbow trout (Oncorhynchus mykiss). Gene expression analysis, revealed that a novel trout TGF-β1 paralogue (TGF-β1b) was more inducible by immune stimulants than the known TGF-β1a and likely represents an important intrinsic factor in macrophages. Both trout TGF-β type I and type II receptor (TGFBR1 and TGFBR2) genes identified encode highly conserved serine/threonine kinases and they are modulated during immune responses. Counter-regulation of the two receptor transcripts in immune stimulated macrophages may indicate regulatory mechanisms operating at the receptor level. Thorough phylogenetic and synteny analysis of the lower vertebrate SOCS system led to further paralogue discovery and uncovered that the proposed teleost-specific SOCS-8 and SOCS-9 members are more likely paralogues of cytokine inducible SH2-containing protein (CISH) and SOCS-5. The trout SOCS-2 subfamily was expanded to three members by cloning SOCS-2b and SOCS-2bRel in addition to SOCS-2a. I revealed for the first time that four paralogues in a SOCS subfamily exist in a teleost by cloning trout CISHa2, CISHb1 and CISHb2 in addition to the known CISHa1. In vivo and in vitro expression of the CISH paralogues suggest possible subfunctionalisation in immunity and development. Attempts to produce trout recombinant proteins of potentially anti-inflammatory cytokines in transiently transfected mammalian cells primed exploitation of these molecules in functional studies.

A new medium, designated Ribose Ornithine Deoxycholate agar (ROD), was developed and used in field trials at two fish farms where fish were known to have ERM. The medium indicated that Yersinia ruckeri could occur in faeces four to six weeks before appearing in the kidney. Fxurther epidemiological studies dealing with fish condition, performance, disease signs and water isolation are presented. These factors are discussed in relation to husbandry and management practices. The minimum uihibitory concentration (MIC) values for 124 strains of F. ruckeri were detemuned. The effect of oxolinic acid, oxytetracycline and a potentiated sulphonamide, on growth patterns over a 72 h period, was also determined. Results showed the bactericidal or bacteriostatic nature of each antimicrobial agent. It was possible to increase the MIC for oxoUnic acid, oxytetracycline and a potentiated sulphonamide usmg an in vitro technique. Attempts to decrease resistance to oxolinic acid were unsuccessful. However, it was possible to reduce the MIC's for o^etracycline and a potentiated sulphonamide. The recovery of Y. ruckeri, after artificial challenge, was less from the faecal and kidney material of a vaccinated group of fish compared with a non-vaccinated group. An E L I S A technique indicated that although there was no detectable serum antibody there was a local mucosal response i n vaccinated fish. Uptake of F. ruckeri antigen was demonstrated in vaccinated and non-vaccinated fish using an immunoperoxidase technique. However, only vaccinated fish appeared to take up the antigen by an active process. A survey of salmonid farms showed that there was a tendency for those sites where ERM had been diagnosed, irrespective of vaccination, to be larger table farms with production ranging up to over 200 tonnes p:a. Certain environmental and husbandry factors were reported as coinciding with the appearance of F. ruckeri. A slight tendency to consider that vaccines had failed i n some way was also indicated. This and the use of antimicrobial agents are discussed.

Graduate

No description available.

No description available.

No description available.

Salmincola edwardsii is an ectoparasitic copepod typically found on the gills of brook trout (Salvelinus fontinalis). Laboratory experiments were conducted to determine: (i) the effects of temperature and photoperiod on early life cycle events, and (ii) the rate of larval development to adult. Egg incubation time, duration of copepodid swimming activity and copepodid survival time all decreased with increasing temperature. Different photoperiods had no effect. Hatching duration and hatching success were not influenced by either temperature or photoperiod. Copepodids remained alive and active for up to 16 days at 8$ sp circ$ and 5 days at 20$ sp circ$C. Adult male copepods were observed at 3 to 8 days after host exposure. They lived for up to 3 days. Adult females became permanently attached to hosts between 11 and 16 days post-infection.

Triploid rainbow trout produced by heat shock and control (diploid) siblings were raised separately at similar density, feeding and water quality regimes. No significant differences in body weight or condition factors were observed; however the weight of the eviscerated carcass was on average 20% higher (P<0.05) in triploid fish compared to diploid fish at 20 and 44 months post-hatching. The effects of triploidy on males were most evident during the final stages of spermatogenesis; in contrast, the gonadal development of triploid females was affected during its early stages, with the majority of the oogonia (30-70%) remaining within the oogonial clusters. A major finding was the presence of male-differentiating areas in most triploid females examined, which by the end of the sampling period appeared as gonadal hermaphrodites. Testicular weight, gonado-somatic index, sperm cell density and spermatozoa motility were significantly lower in triploid than in diploid male siblings, although some triploid males produced viable progeny when crossed to normal (diploid) females. Characterisation of this progeny by image analysis of nuclear DNA revealed the presence of a near-triploid genome. A single 5 month-old juvenile had developed testes in meiotic phase, providing a first evidence for the generation of limited numbers of viable progeny by autotriploid rainbow trout males. A cytogenetic analysis was carried out on monosex diploid and triploid populations of Nile tilapia. Synaptonemal complex analysis in diploid genotypes revealed the presence of an incompletely paired segment in the terminal region of the longest bivalent in heterogametic (XY) genotypes, which was not observed in homogametic genotypes. This unpaired region provides cytological evidence for the chromosomal basis of sex determination in O. niloticus. Meiotic analysis in triploids revealed the presence of longer (P<0.0001) synaptonemal complexes in heterogametic (XXY) than in homogametic (XXX) genotypes, with a significantly different (P<0.0001) nature of pairing evident between both groups. A model to explain the different progress in gametogenesis observed between male and female teleosts is discussed.

Graduation date: 1970

Graduation date: 1971