**ABSTRACT NOT FOR CITATION WITHOUT AUTHOR PERMISSION. The title, authors, and abstract for this completion report are provided below.  For a copy of the full completion report, please contact the author via e-mail at otgorman@usgs.gov or via telephone at 715-682-6163. Questions? Contact the GLFC via email at frp@glfc.org or via telephone at 734-662-3209.**

 

A hyperbaric holding& transport vessel for collection of deepwater fishes for research and broodstock development 

 

Gorman, O.1 and T. D. Keyler2

1U.S. Geological Survey

Lake Superior Biological Station

Ashland, WI 54806

 

2Department of Biology

University of Minnesota

Duluth, MN 55812

 

March 2016

 

ABSTRACT:

 

Barotrauma is an array of physiological responses that are manifested when organisms are subjected to a rapid reduction in barometric pressure. Fish brought to the surface from deepwater (> 30 m) quickly succumb to the effects of barotrauma and the severity of barotrauma increases with depth of capture. In 2012, a program to collect deepwater fishes from Lake Superior was initiated to supply live fish for laboratory research on foraging ecology of siscowet lake trout. The challenge was to collect fish from depths > 100 m and keep them alive despite the effects of severe barotrauma. Protocols were developed to increase the short- and long-term survival of deep-caught fishes suffering from barotrauma, but without rapid recompression and controlled decompression (RRCD). Mortality was high in ciscoes and lake whitefish (100% within 2-5 days) but relatively low in more resilient species, e.g., siscowet lake trout and burbot (< 20% over 30 days), though recovery was prolonged (≥ 30 days). To improve survival and health of deep-caught fishes, a hyperbaric apparatus that performs RRCD on deepwater fishes was designed in 2013, constructed in 2013-2015, and tested in fall 2015. The hyperbaric apparatus for fish (HAfF) consists of two stainless-steel 50-gallon capacity pressure vessels mounted in a stainless-steel transport frame and a hyperbaric control system (HCS) to regulate RRCD in the vessels. The vessels are capable of rapid recompression to 7 atmospheres (equivalent to 70 m depth) and are insulated to limit temperature change to < 2C over 6 hours. Decompression is accomplished by manually adjusting pressure regulators in the HCS to decrease vessel pressure in steps (decompressions stops). The HCS allows custom mixing of oxygen, nitrogen, and air to achieve a desired level of dissolved oxygen prior to recompression of fish. Physical parameters (temperature, pressure, dissolved oxygen, conductivity, and pH) are measured inside each vessel by a multi-parameter instrument and remotely displayed and logged on a computer tablet. Video cameras mounted inside each vessel provide live images and record fish movement and behavior under infrared lighting. The HAfF can be moved and loaded onto a truck bed with a forklift capable of lifting 1500 kg and loaded onto a ship with a crane with similar lifting capacity. While in transit to a laboratory facility, conditions inside the HAfF vessels can be monitored remotely from inside the vehicle cab and adjustments to the HCS can be easily made during short vehicle stops to adhere to a decompression schedule. The HAfF was field tested during two deepwater fish collecting trips in October and November 2015. Fish treated with RRCD did not show improved survival compared to fish not decompressed, although treated fish showed reduced signs of barotrauma. 75% of lake trout and 60% of burbot survived long-term (> 30 days) when treated with RRCD but only 25% of sculpin and 10% of ninespine stickleback survived long-term and no coregonids (ciscoes and lake whitefish) survived beyond 3-4 days. Siscowet and burbot treated with RRCD recovered quickly compared to untreated fish (7 days vs. ~30 days). Our initial trials showed the HAfF worked as designed but additional research is required to refine protocols for live collection, RRCD, and recovery of deepwater fishes. We anticipate that the HAfF will be a useful research tool for understanding barotrauma and the physical limitations of diel migration in deepwater fishes, and may serve as a useful tool for live collection of deepwater ciscoes for broodstock development and wildstock propagation initiatives aimed at recovery of extirpated ciscoes in the Great Lakes.