black fish
n.— «Share fishermen, who are classified self-employed, receive a share of the profits or gross earnings of a fishing boat but research from HM Revenue and Customs (HMRC) has revealed that share fishermen often don’t save for tax and national insurance, and this can cause difficulty when the tax bill finally arrives. There have been several prosecutions brought over what has been labelled “black fish’ caught without any tax being paid.» —“Tax help for share fishermen” Whitehaven News (Whitehaven, Cumbria, United Kingdom) May 24, 2007. (source: Double-Tongued Dictionary)
Further reading
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