Many have looked to Japan for an explanation for these advanced methods. The roe was transplanted to safe pens for incubation and to guard the small fry from predators. Only when sufficiently mature to fend for themselves were they released back into the wild. These days this method is practiced by fisheries throughout the world. Before the Spanish came, the Filipinos also only used large mesh nets when fishing in rivers, lakes or in the sea. This ecologically sound practice protected the young ensuring future good catches. However, the competition brought by the Spaniards resulted in the use of such small mesh nets that the Spanish themselves eventually had to regulate the nets to prevent the destruction of the fisheries. Other Pre-Spanish Filipino industries included the manufacture of liquors and vinegars like tuba, basi, etc., the production of hides for export to Japan, export of edible bird's nests from Northern Palawan to China, the raising and trade of civet cats, the manufacture of gunpowder, the making of wax for export to China, and the making of cotton stockings for export.