Ed Noga has done groundbreaking research on a variety offish. 



Specific immunity protects against a single 

 pathogen. Thus, in some ways, nonspecific 

 immunity can be considered a "natural broad- 

 spectrum protectant." 



"These HLPs were found in the spleen, 

 skin, and gills and are probably in other tissues 

 of catfish," says Noga. "So these HLPs appear to 

 be everywhere. This is significant because it 

 suggests that HLPs may be important in 

 protecting against many diseases. We also found 

 these types of antibiotics in rainbow trout and 

 hybrid striped bass." 



In the study, catfish were exposed to 

 chronic stress — from overcrowding and 

 elevated ammonia — for several weeks. This 

 stress caused a significant decline in HLP levels 

 in the skin without any visibly apparent change 

 in the health of the fish. This indicates that HLPs 

 could alert farmers when their fish are at risk for 

 becoming sick, but before any visible clues are 

 apparent. 



"This suggests that monitoring HLP levels 

 in the skin — especially during early stages of 

 stress — can help farmers to detect problems 

 before they become catastrophic," says Noga. 



The identification of a stress test usable in 

 the field would be important for the aquaculture 

 industry where fish are reared under very high 



stocking densities, offering potential for disease 

 outbreaks. 



The channel catfish industry is the largest 

 aquaculture sector in the United States, 

 generating over $400 million annually, 

 according to Noga. 



In North Carolina, the total estimated value 

 of catfish aquaculture in 2000 was nearly $3.5 

 million, according to the N.C. Department of 

 Agriculture & Consumer Services. 



"One of the major goals of a successful 

 aquaculture enterprise is to avoid a disease 

 epidemic," says Noga. "This typically involves 

 stress reduction in fish stocks." 



However, there are no practical tests 

 available for fish farmers to use in detecting fish 

 stress, according to Noga "All the stress tests for 

 fish are too expensive, labor-intensive, or not 

 very useful in assessing health in the field," he 

 adds. "We are hoping to develop a test for fish 

 farmers that can done on-site in less than 30 

 minutes." 



Hodson says this research has important 

 implications for the marine aquaculture industry. 

 "There are few antibiotics to treat fish," he adds. 

 "This test might give growers a chance to detect 

 health problems earlier — and thus avoid the 

 need for drug intervention." 



SEA 



SCIENCE 



FRG Project 



Through a N.C. Fishery Resource Grant 

 (FRG), Noga is working with veteran crabber 

 Robin Doxey of Merritt and Bill Gordon of 

 Bethyl Labs in Texas to develop a blood test for 

 peelers — crabs that are about to shed their 

 shells. The FRG program is funded by the N.C. 

 General Assembly and administered by North 

 Carolina Sea Grant. 



Noga's goal is for shedders and fishery 

 managers to administer a simple test. 



"This test is based on the same principal as 

 the one for channel catfish," says Noga "The 

 blue crab has a potent antibiotic in its blood. 

 Crabs from highly stressed environments have 

 less of this antibiotic compared to crabs that are 

 less stressed. Crabs with shell disease have even 

 less of this antibiotic." 



In North Carolina blue crabs, including 

 soft and peeler crabs, are a valuable fishery. 

 From 1999 to 2000, the value of soft-shell crabs 

 jumped from about $2.1 million to $3.3 million, 

 according to the N.C. Division of Marine 

 Fisheries. 



"Mortality is a serious concern in shedding 

 operations and has in many instances caused 

 considerable economic losses," adds Noga. 



Shedding operations use high-density, 

 recirculating systems that can increase the risk 

 of disease and mortality, according to Noga. 

 Now, crabbers rely on observation and 

 measures of water quality, including dissolved 

 oxygen and ammonia levels, to determine the 

 health of crabs. 



"Simply observing a crab is a very 

 inaccurate indicator of health or survivability, 

 unless the crab is near death," says Noga 

 "While maintaining high dissolved oxygen and 

 low ammonia levels is important for shedding, 

 problems often occur when these levels are 

 normal because you cannot measure all water 

 quality factors that adversely affect blue crabs." 



With the test, crabbers will be able to 

 quickly and precisely determine when crabs are 

 stressed so that corrective measures can be taken 

 before mortality occurs. 



"We hope that these types of tests will 

 become one of the most useful tools that we 

 have for health management of aquatic 

 populations," Noga says. □ 



COASTWATCH 25 



