Sport Fishing - - FISH FACTS - — Ben Dig­gles

We run sport-fish­ing tours out of the re­mote rivers in the New Bri­tain prov­ince of Pa­pua New Guinea. Be­sides catch­ing the no­to­ri­ous PNG black bass (our main tar­get), we also catch th­ese in­ter­est­ing grouper on lures while cast­ing at snags or other struc­ture in lower rivers. I’ve al­ways won­dered what they are. Some have white dots, and oth­ers are just black. Are those the same species? I have caught them more than 2 feet long in the fresh wa­ter of rivers from the mid­dle reaches down to the river mouth.

Ric­card Reimann

Baia Wilder­ness Bass Fish­ing Lodge Pa­pua New Guinea

What you have been catch­ing there, Ric­card, are white-dot­ted grouper ( Epinephelus polystigma). Also known as white-spot­ted rock cod, this species oc­curs in es­tu­ar­ies and rivers from the Philip­pines south through eastern In­done­sia, PNG and the Solomon Is­lands to north­ern Queens­land, Australia. It ap­pears to have two main forms, ei­ther with white dots or a dark­brown or black blotchy color pat­tern. In some parts of their range, white-dot­ted grouper are known by na­tives as “lazy fish,” easy to spear when they ag­gre­gate near man­groves in shal­low wa­ter at night, rest­ing on the bot­tom with their backs out of the wa­ter. Be­cause of this be­hav­ior, the species quickly be­comes rare around ar­eas in­hab­ited by humans. E. polystigma is a rea­son­ably small grouper, grow­ing only to 20 inches or so; thus, the big­gest ones you have been catch­ing at 24 inches ap­prox­i­mate their max­i­mum size. You must be fish­ing in some re­mote ar­eas to catch them that big. Sci­en­tists know very lit­tle about this species, though it’s usu­ally un­der­stood to be soli­tary — the shal­low-wa­ter ag­gre­ga­tions are prob­a­bly spawn­ing be­hav­ior, as they oc­cur mainly on new-moon phases and the fish taken dur­ing this time are run­ning ripe. White-dot­ted grouper sam­pled be­tween 8 and 15 inches long proved to be ma­ture fe­males, and all fish above 18 inches long were ma­ture males, sug­gest­ing that th­ese fish may, like other ser­ranids ( groupers), ma­ture first as fe­males be­fore chang­ing sex into males.

White-dot­ted grouper

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