Oceanographic Basis of a DMS-Related Atlantic Cod (Gadus morhua) Fishery Problem: Blackberry Feed

Abstract

Atlantic cod (Gadus morhua) caught along the Labrador and Newfoundland coasts and in the Strait of Belle Isle often smell strongly of sulfur, a problem locally called "blackberry feed". Early studies have shown that the sulfurous-smelling cod had fed almost exclusively on the pteropod Limacina helicina and that dimethylsufide (DMS) was responsible for the odor. In August 1991, we conducted a cruise in the northeastern Gulf of St. Lawrence and in the Strait of Belle Isle in order to confirm the algal origin of dimethylsulfoniopropionate (DMSP, the precursor of DMS) and to determine the factors responsible for its transfer in the food web. A significant correlation was found between the distribution of DMSP and the abundance of microflagellates, dinoflagellates, cryptomonads, and prymnesiophytes (mostly Chrysochromulina spp.). The concentration of DMSP in L. helicina and in particles were also linearly related, suggesting rapid accumulation of DMSP in pteropod. The weight-specific DMSP content of L. helicina was always high (1–21 mg DMSP/g) and apparently sufficient to create blackberry feed symptoms in cod. Results from bioassay experiments demontrated that L. helicina may significantly influence the DMSP–DMS dynamics in subarctic waters.

Metabolism of dimethylsulfoniopropionate (DMSP) by juvenile Atlantic menhaden Brevoortia tyrannus

“…Even the relatively small meal we provided resulted in tissue DMSP concentrations higher than those that have been observed to cause offensive tastes and odors via DMS production (Ackman et al 1966, Levasseur et al 1994. Menhaden are key forage items for piscivorous table fish such as bluefish, striped bass, and bonito (Ahrenholz 1991, Walter & Austin 2003.…”

“…DMS, however, has a potent taste and odor, which are offensive at high micromolar concentrations. When DMSP that has passed up food chains accumulates in the tissues of fish used as human food, postmortem breakdown to DMS can impart repellent tastes and odors to the fish (Ackman et al 1966, Levasseur et al 1994, even to the extent of sometimes forcing large quantities of fish or fish products to be discarded. Menhaden are a principal forage species for commercially important piscivores such as bluefish Pomatomus saltatrix, striped bass Morone saxatilis, and bonito Sarda sarda (Ahrenholz 1991, Walter & Austin 2003.…”

Exceptional accumulation and retention of dimethylsulfoniopropionate by molluscs

“…With respect to the open ocean, certainly herbivorous pteropods 29 (planktonic molluscs) have the potential to be major phytoplankton and DMSP consumers at the 30 times and places of their blooms. [8] In short, there is every reason to believe that molluscs often 31 process a sizable fraction of local phytoplankton DMSP production, poising them to exert strong 32 effects on local DMSP/DMS dynamics.…”

“…Levasseur et al [8] report, for example, that when free-living Western Atlantic cod 247 populations become enriched with tissue DMS(P) to a commercially detrimental extent, the 248 problem lasts only 2-3 weeks.…”

“…Distinctively tight retention, as we are arguing is common in Pteropods (planktonic molluscs) are well documented to be principal vectors for 388 commercially detrimental accumulations of DMS(P) in fish such as chum salmon (Oncorhynchus keta) and cod (Gadus morhua). [8,17,18] The pteropods feed directly or indirectly 390 on DMSP-producing phytoplankton, and the fish obtain DMSP when they feed on the pteropods.…”