Stephen D. Eddy

Microbiology of summer flounder Paralichthys dentatus fingerling production at a marine fish hatchery

Abstract The microbiology of summer flounder, Paralichthys dentatus, fingerling production was monitored over the course of 10 production cycles during 1996–1999 at a commercial marine fish hatchery. Samples of the rearing water, fish larvae and live feed were analyzed to quantify the total heterotrophic bacteria (marine agar) and total presumptive vibrios. Selected bacterial isolates were characterized to the group or species level. The tank water was compared between two larviculture methods to see if greenwater densities or the timing of fish movements could affect the tank microbiology. The extensive use of phytoplankton as rotifer enrichment and as greenwater reduced the incidence of vibrios as a percentage of total heterotrophs in the rotifers and water. Rinsed enriched Artemia had high levels of vibrios, and the fish larvae experienced increased mortality during the period of Artemia feeding although known bacterial fish pathogens were not detected at significant levels. The microbiota of the rearing water and fish intestine were similar to that of the live feed being utilized at the time of the sampling. A succession of bacterial phenotypes was observed in the rearing water and the fish intestine from day 1 to day 90 post-hatch, and the fish larvae showed evidence of the development of a stable indigenous microbiota during and after metamorphosis. Acinetobacter, Agrobacterium, Flavobacterium, Moraxella and Pseudomonas were the dominant bacterial groups in phytoplankton, rotifers and the early larval fish and tanks. However, Artemia and older larval stages and tanks showed a shift towards the microbiota with higher levels of Vibrio and Enterobacter. Bacillus was detected in juvenile fish but not in larval stages. The results provide a database for analyzing the role of the microbiota in health and disease of summer flounder and suggest that this microbiota may be amenable to probiotic type manipulations.

Nursery-phase Culture of Green Sea Urchin Strongylocentrotus droebachiensis using “On-bottom” Cages

Abstract Sea urchin hatchery techniques are well established, but cost effective grow-out strategies are still under development. Juvenile green sea urchins (Strongylocentrotus droebachiensis) with a test diameter of less than 15 mm are vulnerable to predation when released into the wild and mortality can be high; therefore a protected nursery phase is required. This study investigated the feasibility of a cost effective on-bottom nursery cage system to provide protection at this stage. Wild-caught juvenile urchins (average diameter 7.93 ± 0.65 mm) were held in specially designed high-density polyethylene (HDPE) mesh tubes, 50 per tube, at two lease sites in Penobscot Bay, ME. Replicate tubes were placed on 3 bottom types (mussel, cobble, and ledge) at the Sloop Island site and on cobble bottom type at the Job Island site. Groups of urchins were counted and measured 5 wk, 3 mo, and 6 mo after placement to gauge handling mortality, growth, and survival. Handling mortality after 5 wk was 5% with no significant difference between treatments. Final survival indicated that cobble bottom type supported the highest survival at Job Island (89%) and Sloop Island (71%), followed by Sloop mussel (59%) and Sloop ledge (56%). After 6 mo the average diameter reached 11.08 ± 1.49 mm. Final average test diameter was significantly larger at Sloop ledge (12.17 mm) and Sloop mussel (12.58 mm), than at Sloop cobble (9.83 mm) and Job cobble (9.66 mm). These results suggest on-bottom culture through the critical nursery phase is technically feasible and may represent an economical way to rear hatchery produced green sea urchin seed to the “planting out” size.

Solar-dried kelp as potential feed in sea urchin aquaculture

Over the past two decades, fishery landings for the highly valued green sea urchin (Strongylocentrotus droebachiensis) have decreased significantly in the Gulf of Maine. Methods for sea urchin aquaculture have been developed in the region, but further growth of the industry is inhibited by the expense of formulated feeds. A potential low-cost solution to this issue is to take advantage of the region’s developing sea vegetable aquaculture industry. A feeding trial was conducted with juvenile hatchery-reared urchins comparing somatic and gonadal growths when fed either fresh wild Saccharina latissima, dried S. latissima, fresh laboratory-reared Porphyra umbilicalis, or the formulated Nofima diet. Somatic and gonadal growths of urchins fed dried S. latissima were intermediate to those fed fresh macroalgae (S. latissima or P. umbilicalis) and the formulated Nofima diet, with significantly faster growth observed in urchins fed the formulated diet and significantly slower growth seen in those fed the fresh macroalgae diets. In light of these results, we propose that dried kelp could suffice as a potential feed in sea urchin aquaculture.