Research Highlights

Aquaculture/Fisheries Center Research Highlights

Baitfish

Identification of key nutrients in baitfish broodstock diets to improve egg and larval quality
Rebecca Lochmann and Nathan Stone

Baitfish farmers now have the technology to spawn fish indoors. However, survival rates of baitfish spawned indoors are highly variable before exogenous feeding is initiated. During this critical period larvae are totally dependent on stored nutrients originating primarily from the mother. Maternal broodstock nutrition is known to affect egg and larval quantity and quality in fishes. Diet lipid and protein composition can be manipulated in other species to improve the reliability of spawning and the quality of offspring produced.

A series of feeding trials are being conducted over a 5-year period with fathead minnows and golden shiners. Dietary lipids and proteins are being manipulated in an attempt to optimize egg production and fry survival.

Dietary lipids affected the fatty acid composition of the eggs but the lipid sources had similar effects on egg production, egg size and fry size and hardiness equally. There were no clear advantages of using one lipid source over another. Egg diameter and number declines over time during the spawning season in fathead minnows regardless of diet. Results are still pending for golden shiners fed similar diets. Stress tests in which fry are exposed to high pH show some dietary influence, but the data is variable and the results are not definitive. This work is potentially applicable to many areas of the US, as these fish are grown indoors in temperate climates. There are currently no dietary recommendations for baitfish broodstock – however, there is no apparent advantage to use of marine fish products in the diets, which may reduce diet cost and enhance sustainability of the industry.
The effects of isopropylmethylphosphonic acid on golden shiners
Rebecca Lochmann and Steve Lochmann

Chronic toxicity tests were conducted in channel catfish and golden shiners exposed to sublethal levels of IMPA in tanks. Channel catfish fry of 0.75–1.00 g size were acclimated to experimental conditions in tanks adjacent to the recirculating system for 2 weeks. During this time the fish were fed a commercial 36%-protein catfish diet twice daily while the temperature was gradually adjusted to 25 oC and the light cycle was maintained at 12h light/12h dark. Near the end of this period, each independent recirculating system was dosed with a different sublethal concentration of IMPA (0.0 (control), 0.1, 1.0, 10.0 or 75 mg/L). During the experiment fish continued to receive the 36%-protein diet twice daily. Fish were weighed by tank every two weeks to track growth. The analyzed IMPA concentrations for growth trial 1 were 0, 0.33, 0.82, 7.83, and 55 mg/L. Growth, survival and liver glycogen in channel catfish were all affected by IMPA concentration, although there was not a clear dose-response relationship for any of these parameters. Although pH decreased with increasing IMPA concentration in the water, the responses of fishes exposed to intermediate doses of IMPA seemed to differ most from the control.

A similar protocol was followed for golden shiners with an average individual initial weight of 1.06 g. The exposure concentrations of IMPA were 0.0, 0.1, 1.0, 10.0 and 75.0 mg/L. Growth was affected by IMPA concentration, although no dose-response relationship was observed. Overall survival was not affected by IMPA dose, although the rate of mortality during the study was affected by IMPA. Again, there was no clear dose-response relationship. Fish exposed to 0.1 mg IMPA/L showed the greatest contrast in patterns of growth and survival compared to fish maintained at the other concentrations.