Evaluation of Off-Season Spawning Techniques & Larval Diet Supplementation of Yellow Perch
Mark Rath - (Master's thesis 2004)

At a 2001 roundtable meeting attended by over half of Maryland's foodfish producers, shortage of supply and high cost of yellow perch fingerlings were cited as a major bottleneck in successful perch production. The ability to produce multile crops of fingerlings annually could solve both of these difficulties. Using the available knowledge of perch physiology and culture techniques, and off-season spawning techniques that have been successful in other species of fish, an experiment was designed to try and address these difficulties. Specific research objectives include: 1. Investigate off-season spawning of yellow perch broodstock in batches to produce multiple crops of fry annually. 2. Evaluate effects of live food enrichments on fry survival.      In the off-season spawning research component, eighteen month old fish (mean weight: 250 g) were stocked in a 1:1 male to female ratio. Fish were divided into four groups (one for each season, Spring, Summer, Fall & Winter) & acclimated to the same conditions. The temperature & light cycle of each group was manipulated independently to shift seasonal conditions & induce spawning. Some fish from Summer, Winter and Spring(2) Groups were injected with HCG or implanted with LHRH. Fish were allowed to tank spawn, but fertilization rates were higher when fish were strip spawned. Eggs were hatched & larvae were monitored daily to observe feeding behavior & development.

Cumulative Number of Egg Ribbons Released In All Spawning Periods

Preliminary conclusions of this research include:
1. Shifting the photo-thermal regime out of phase has resulted in successful off-season spawning.
2. Tank spawning resulted in poor fertilization; strip spawning and use of hormone injections are recommended.
3. Compared to other species, yellow perch are more difficult to successfully spawn indoors. Advanced techniques & highly trained staff are required .
4. Problems with observed poor egg ribbon matrix quality should not prevent yellow perch producers from adopting this off-season spawning technique.
5. Larval survival can be improved by using an enrichment product to increase the essential fatty acids in traditional live foods.
6. Larvae can be weaned onto manufactured diets to further improve survival and reduce production costs.

Striped bass health and Mycobacterium  

      HPL has been working in conjunction with the Sarbanes Cooperative Oxford Laboratory (SCOL) since 1997 on issues of fish health in the Chesapeake Bay. HPL's role has been to supplement SCOL monitoring efforts with the collection of physiological data, and design and implementation of experiments aimed at furthering our understanding of the causes, progression, transmission, and outcomes of fish diseases. In 1999, nearly 50% of Chesapeake Bay striped bass exhibited internal symptoms of chronic bacterial disease and the percentage of infected fish continues to grow. The mycobacteria responsible for these infections in striped bass can also cause persistent skin infections in humans. The fate of infected fish is unknown, but it is presumed that mortality is the end result of the disease. Information on progression and fate of these fish is needed for management of the fishery. This disease appears to be a significant chronic threat to the health and sustainability of the striped bass population in Chesapeake Bay. There are critical needs for rapid, non-destructive diagnostic methods, estimation of mortality rates, identification of mode of transmission, and evaluation of management measures that could reduce the disease's overall impact. We continue to provide assistance in monitoring the prevalence of ulcerative dermatitis in Chesapeake Bay and assessing the nutritional health of striped bass.

           Other research activities related to this project include:

• Sample striped bass spawning stock on the Choptank and Nanticoke River spawning grounds during the month of April for the presence of external abnormalities.
• Spawn captured broodstock, rear larvae and fingerlings and maintain juvenile fish for experiments to be performed at Oxford.

• Assisting MDNR with surveys of the prevalence of disease (Ulcerative Dermatitis and Mycobacteriosis).
• Surveys of the external condition of Choptank and Nanticoke River spawning stock captured by electrofishing.
• Investigating the possibility of vertical disease transmission (from parent to offspring) by sampling gametes from spawning stock of the Choptank and Nanticoke rivers.
• Relation of nutritional condition of striped bass to disease status.
• Caging studies with menhaden in suspected areas of Pfiesteria activity