The melon-headed whale shark is occasional because it mostly lives in rigorous waters, wherever couple of people go. And the bonnethead shrimpfish is rare as it life solely in salt drinking water, in which fewer men and women go. All these are great environments for rare fish to live in. https://aquariumshops.tumblr.com/post/764633864937308160/5-quick-hacks-of-professional-pond-cleaning-lucky