Alarm substance recognition and predator avoidance by chinook salmon (Oncorhynchus tschawytscha) following exposure to an organophosphate pesticide.

The sense of smell in fish is thought to be important for behaviors associated with alarm scent recognition and predator avoidance. Olfactory function of juvenile chinook salmon was evaluated in two separate experiments following 2-h immersion exposures to 0, 1, 10, or 100 microg diazinon/L. In the first test system, groups of 10 salmon were transferred to the prechoice zone of a Y-maze fluviarium with parallel streams of water. A dilute alarm scent composed of either chinook skin extract or L-serine was pumped into the water supply of one arm. Fish were allowed to choose either upstream arm by raising a containment screen for 10 min, then their positions were photographed and the screen lowered. In the second test system the relationship of diazinon exposure to predation susceptibility was directly examined by transferring groups of 20 salmon (10 diazinon-exposed, 10 control) to troughs containing a protective cover. These salmon were given two olfactory warnings by delivering conspecific skin extract to both their transfer container and the predation tank they entered. After a 2-min prey acclimation period, larger predator rainbow trout were allowed access to the downstream section of the tank containing the test salmon. The combined fish were observed until approximately 50% of the prey fish had been consumed. Statistical comparisons indicated that although the salmon did avoid the water streams containing alarm scents, none of the diazinon exposure levels resulted in significantly different outcomes from the controls (alpha=0.05) in either the two-choice maze study or the predation study. Possible environmental and population implications are discussed in light of related olfaction and diazinon studies.

Extremophile extracts and enhancement techniques show promise for the development of a live vaccine against Flavobacterium columnare.

The effects of temperature, ionic strength, and new cryopreservatives derived from polar ice bacteria were investigated to help accelerate the development of economical, live attenuated vaccines for aquaculture. Extracts of the extremophile Gelidibacter algens functioned very well as part of a lyophilization cryoprotectant formulation in a 15-week storage trial. The bacterial extract and trehalose additives resulted in significantly higher colony counts of columnaris bacteria (Flavobacterium columnare) compared to nonfat milk or physiological saline at all time points measured. The bacterial extract combined with trehalose appeared to enhance the relative efficiency of recovery and growth potential of columnaris in flask culture compared to saline, nonfat milk, or trehalose-only controls. Pre-lyophilization temperature treatments significantly affected F. columnare survival following rehydration. A 30-min exposure at 0 degrees C resulted in a 10-fold increase in bacterial survival following rehydration compared to mid-range temperature treatments. The brief 30 and 35 degrees C pre-lyophilization exposures appeared to be detrimental to the rehydration survival of the bacteria. The survival of F. columnare through the lyophilization process was also strongly affected by changes in ionic strength of the bacterial suspension. Changes in rehydration constituents were also found to be important in promoting increased survival and growth. As the sodium chloride concentration increased, the viability of rehydrated F. columnare decreased.

Immunocompetence of juvenile Chinook salmon against Listonella anguillarum following dietary exposure to Aroclor 1254.

Controlled laboratory challenges with pathogenic Listonella (formerly Vibrio) anguillarum bacteria were used to examine potential effects of dietary exposure to polychlorinated biphenyls (PCBs) on the growth and immunocompetence of juvenile Puget Sound (WA, USA) Chinook salmon (Oncorhynchus tschawytscha). Salmon were fed four levels of the PCB congener mixture Aroclor 1254 for 28 d to bracket likely exposure to PCBs in the lower Duwamish waterway near Seattle, Washington, USA. Fish were transferred to five replicate tanks per dose, exposed to L. anguillarum, and monitored for 14 d. Half the PCB-dosed fish were vaccinated against L. anguillarum, and specific immunity was allowed to develop in this group for three weeks prior to challenge. All mortalities following challenge were individually sampled for bacteria to identify the cause of death. The data indicate that dietary PCB exposure, even at relatively high levels, did not have a significant effect on growth, innate disease resistance, or acquired immunity to L anguillarum. The controlled laboratory experiments in this study suggest that the immune system of Chinook salmon is not sensitive to orally delivered PCBs at environmentally relevant concentrations.

Immunocompetence of juvenile chinook salmon against Listonella anguillarum following dietary exposure to polycyclic aromatic hydrocarbons.

Juvenile chinook salmon (Oncorhynchus tschawytscha) were fed a mixture of 14 polycyclic aromatic hydrocarbon (PAH) compounds that reflected the PAH composition of salmon stomach contents in an urban estuary of Puget Sound, Washington (USA). Following a 28-d dietary exposure, a standardized Listonella anguillarum challenge model was used to determine whether PAH exposure (16, 64, and 252 mg/kg wet wt feed) causes reduced disease resistance under the conditions examined in this study. To assess innate immunity, five replicate groups of fish per dose were acclimated for one week, exposed to a lethal concentration 60 of bacteria, and monitored for 14 d. In a parallel experiment, the effects of PAH exposure on the acquired immune response were examined by immersion vaccinating fish against L. anguillarum and allowing specific immunity to develop for three weeks prior to challenge. All mortalities were aseptically sampled to confirm L. anguillarum infections. No significant differences in fish length, weight, or coefficient of condition were observed. These controlled laboratory experiments suggest that dietary exposures to an environmentally relevant mixture of PAH compounds do not alter the immunocompetence or growth of juvenile chinook salmon.