Fish shape for pgf

gistfile1.tex

\documentclass[tikz]{standalone}

\makeatletter
\pgfdeclareshape{fish}
{
  \savedmacro\fishpoints{
    \pgfextract@process\centerpoint{%
      \pgf@x=.5\wd\pgfnodeparttextbox%
      \pgf@y=.5\ht\pgfnodeparttextbox%
      \advance\pgf@y by-.5\dp\pgfnodeparttextbox%
    }
    \pgfextract@process\innerradius{
      \centerpoint%
      \pgfmathsetlength\pgf@yb{\pgfkeysvalueof{/pgf/inner ysep}}%
      \advance\pgf@y by\pgf@yb%
      \pgfmathsetlength\pgf@xb{\pgfkeysvalueof{/pgf/inner xsep}}%
      \advance\pgf@x by\pgf@xb%
      % Adjust to minimum dimensions.
      \pgfmathsetlength\pgf@yc{\pgfkeysvalueof{/pgf/minimum height}}%
      \ifdim\pgf@y<.5\pgf@yc%
        \pgf@y=.5\pgf@yc%
      \fi%
      \pgfmathsetlength\pgf@xc{\pgfkeysvalueof{/pgf/minimum width}}%
      \ifdim\pgf@x<.5\pgf@xc%
        \pgf@x=.5\pgf@xc%
      \fi%
    }
    \pgfextract@process\outerradius{
      \innerradius%
      \pgfmathsetlength{\pgf@xb}{\pgfkeysvalueof{/pgf/outer xsep}}%  
      \advance\pgf@x by\pgf@xb%
      \pgfmathsetlength{\pgf@yb}{\pgfkeysvalueof{/pgf/outer ysep}}%  
      \advance\pgf@y by\pgf@yb%
    }
    \pgfextract@process\tip{
      \innerradius
      \pgf@xc1.5\pgf@x
      \pgf@process{\centerpoint}
      \advance\pgf@x\pgf@xc
    }
    \pgfextract@process\finmidpoint{
      \innerradius
      \pgf@xc-2.75\pgf@x
      \pgf@process{\centerpoint}
      \advance\pgf@x\pgf@xc
    }
    \pgfextract@process\upperfin{
      \innerradius
      \pgf@yc\pgf@y
      \pgf@process{\finmidpoint}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\lowerfin{
      \innerradius
      \pgf@yc-1\pgf@y
      \pgf@process{\finmidpoint}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\findent{
      \innerradius
      \pgf@xc-2.5\pgf@x
      \pgf@process{\centerpoint}
      \advance\pgf@x\pgf@xc
    }
    \pgfextract@process\upperfincontrol{
      \innerradius
      \pgf@yc0.2\pgf@y
      \pgf@process{\findent}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\lowerfincontrol{
      \innerradius
      \pgf@yc-0.2\pgf@y
      \pgf@process{\findent}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\rightbodycontrol{
      \innerradius
      \pgf@xc-.75\pgf@x
      \pgf@process{\centerpoint}
      \advance\pgf@x\pgf@xc
    }
    \pgfextract@process\upperrightbodycontrol{
      \innerradius
      \pgf@yc4\pgf@y
      \pgf@process{\rightbodycontrol}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\lowerrightbodycontrol{
      \innerradius
      \pgf@yc-4\pgf@y
      \pgf@process{\rightbodycontrol}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\leftbodycontrol{
      \innerradius
      \pgf@xc-1\pgf@x
      \pgf@process{\centerpoint}
      \advance\pgf@x\pgf@xc
    }
    \pgfextract@process\upperleftbodycontrol{
      \innerradius
      \pgf@yc-1\pgf@y
      \pgf@process{\leftbodycontrol}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\lowerleftbodycontrol{
      \innerradius
      \pgf@yc\pgf@y
      \pgf@process{\leftbodycontrol}
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\northeast{
      \innerradius
      \pgf@xc\pgf@x
      \pgf@yc\pgf@y
      \pgf@process{\centerpoint}
      \advance\pgf@x\pgf@xc
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\southeast{
      \innerradius
      \pgf@xc\pgf@x
      \pgf@yc\pgf@y
      \pgf@process{\centerpoint}
      \advance\pgf@x\pgf@xc
      \advance\pgf@y-\pgf@yc
    }
    \pgfextract@process\northwest{
      \innerradius
      \pgf@xc\pgf@x
      \pgf@yc\pgf@y
      \pgf@process{\centerpoint}
      \advance\pgf@x-\pgf@xc
      \advance\pgf@y\pgf@yc
    }
    \pgfextract@process\southwest{
      \innerradius
      \pgf@xc\pgf@x
      \pgf@yc\pgf@y
      \pgf@process{\centerpoint}
      \advance\pgf@x-\pgf@xc
      \advance\pgf@y-\pgf@yc
    }
    \addtosavedmacro{\tip}
    \addtosavedmacro{\centerpoint}
    \addtosavedmacro{\upperfin}
    \addtosavedmacro{\lowerfin}
    \addtosavedmacro{\findent}
    \addtosavedmacro{\upperfincontrol}
    \addtosavedmacro{\lowerfincontrol}
    \addtosavedmacro{\upperrightbodycontrol}
    \addtosavedmacro{\upperleftbodycontrol}
    \addtosavedmacro{\lowerrightbodycontrol}
    \addtosavedmacro{\lowerleftbodycontrol}
    \addtosavedmacro{\northeast}
    \addtosavedmacro{\southeast}
    \addtosavedmacro{\northwest}
    \addtosavedmacro{\southwest}
  }
  \anchor{center}{
    \fishpoints
    \centerpoint
  }
  \anchor{east}{
    \fishpoints
    \tip
  }
  \anchor{west}{
    \fishpoints
    \findent
  }
  \anchor{north east}{
    \fishpoints
    \northeast
  }
  \anchor{south east}{
    \fishpoints
    \southeast
  }
  \anchor{north west}{
    \fishpoints
    \northwest
  }
  \anchor{south west}{
    \fishpoints
    \southwest
  }

  \backgroundpath{
    \fishpoints
    \pgfpathmoveto{\tip}
    \pgfpathcurveto{\upperrightbodycontrol}{\upperleftbodycontrol}{\upperfin}
    \pgfpathcurveto{\upperfincontrol}{\lowerfincontrol}{\lowerfin}
    \pgfpathcurveto{\lowerleftbodycontrol}{\lowerrightbodycontrol}{\tip}
    \pgfpathclose
  }
}
\makeatother

\begin{document}
\begin{tikzpicture}
  \node[inner sep=0, draw=blue, fill=red, fish] (tuna) {tuna};
  \node[draw=blue, fill=red, fish] at (1, 1) (barb) {barb};
  \draw[gray] (tuna.north east) -- (tuna.south east) -- (tuna.south west) -- (tuna.north west) -- cycle;
  \draw[gray] (barb.north east) -- (barb.south east) -- (barb.south west) -- (barb.north west) -- cycle;
\end{tikzpicture}
\end{document}