Nicholas P. Brown

Flatfish Farming Systems in the Atlantic Region

The farming of flatfish in the Atlantic region is increasing steadily, and members of this group of fish are well represented in the lists of “new species for aquaculture”. This sector is currently dominated by the farming of around 5000 MT/year of European turbot (Scophthalmus maximus). Other species of importance include the Atlantic halibut (Hippoglossus hippoglossus), sole (Solea solea, S. senegalensis), and the summer flounder (Paralichthys dentatus). Various systems, both sea-based and land-based, are used to grow these species to harvest weight. Flatfish are well suited to land-based farming and can be grown in a variety of tank types. Some species, particularly European turbot and Atlantic halibut, can be held at high densities (50 to 75 kg/m2), and the use of multiple layers within tanks further improves productivity for halibut. Cage systems for flatfish are generally adapted from those used to raise round fish and incorporate rigid bases. Surface cages are more widespread, but the use of submersible cages for farming flatfish offshore is under investigation. This article provides a summary of the species of interest, the conditions under which they are grown, the types of systems currently in use, and the major factors that determine their suitability.

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.