Ancient Hawaiian aquaculture

Before contact with Europeans, the Hawaiian people practiced aquaculture through development of fish ponds (loko ia), the most advanced fish-husbandry among the original peoples of the Pacific. While other cultures in places like Egypt and China also used the practice, Hawaii's aquaculture was very advanced considering the much smaller size of the area of Hawaii compared to other aquacultural societies. Hawaiian fishponds were typically shallow areas of a reef flat surrounded by a low lava rock wall (loko kuapa) built out from the shore. Several species of edible fish (such as mullet) thrive in such ponds, and Hawaiians developed methods to make them easy to catch.

The Hawaiian fishpond was primarily a grazing area in which the fishpond-keeper cultivated algae; much in the way cattle ranchers cultivate grass for their cattle. The porous lava walls let in seawater (or sometimes fresh or brackish water, as in the case of the "Menehune" fishpond near Līhue, Kauai), but prevent the fish from escaping. Fishponds were located next to the mouth of a stream, so by opening a sluice gate the pondkeeper provided the fish with water rich in nutrients that had passed through inland, terraced pondfields and returned to the stream. At the time of Captain James Cook's arrival, there were at least 360 fishponds producing 900,000 kg of fish per year.

Types of fishponds
There were four basic types of fishponds developed within the Ahupua'a known in ancient Hawaii. The four types of fishponds were freshwater taro fishponds (loko i'a kalo), other freshwater ponds (loko wai), brackish water ponds (loko pu'unone), and seawater ponds (loko kuapa).

Taro fishponds (loko i'a kalo) were usually seen inland and were used to cultivate Taro as well as grow fish, such as mullet, silver perch, Hawaiian gobies, Freshwater prawn, and green algae. Taro fish ponds were usually located close to the sea and contained surplus of fish. Fish were also able to directly enter the taro patch-fishponds from the sea through newly created artificial estuary. Fish in these ponds thrived and were able to survive the transition from seawater to freshwater. They also helped the taro in these ponds by feeding on insects and ripe leaf stems of taro. The taro would help prevent silt by catching it before it would go downstream into the ocean. Planting between the wetland areas would also help provide green manure, medicines and other products.

Loko wai are other freshwater ponds that are seen inland and usually were excavated by hand from natural depressions like lakes or ponds and were supplied from naturally created water supplies (i.e., streams, rivers, springs, etc.). These ponds contained native species of freshwater prawn and fishes that migrate from the sea and into freshwater (i.e., mullet, milkfish. etc.). Fishes in these ponds were often harvested when spawning fish moved seaward, usually during full moons in the spring.

Brackish water ponds (loko pu'unone) were seen very close to the ocean and excavated by hand from natural bodies of water that have been stranded by sea-level change, or by creating an earth embankment with mud, sand, and coral. This made a wall that separated the pond from the ocean. However, these ponds were still connected to the ocean via small canals which would allow seawater fished to enter the fishpond during the rising tide. These brackish-water ponds were very productive and was filled with many different types of species.

According to B.A. Costa-Pierce, seawater ponds were the "ultimate aquaculture achievement of native Hawaiians and a valuable contribution to native engineering and subsistence food production." These ponds were constructed by a seawall, usually made of coral or lava rocks, with lengths of these walls ranging from 46 to 1,920 m. Coralline algae was gathered and used as a natural cement to hold and strengthen the walls. These ponds were very diverse, usually containing about 22 species of marine life. One of the most important features of these ponds were canals that was connected directly to the sea and had a grate made of wood and ferns that sat in the middle of these canals. These innovative grates allowed for very small fish to enter the pond and prevented bigger and mature fish from leaving. Harvesting timing and methods were usually determined by the behavior of the fish. For example, during migration seasons for fishes such as milkfish and mullet that migrate to the ocean to spawn, keepers of the fishpond would set out nets on the pond side of the grates and watch as the fishes trapped themselves as they tried to reach the sea.

Restoration
Several fishponds have been restored in recent years. Although fishponds were developed on most islands, the largest number were found in Keehi Lagoon, Pearl Harbor, Maunalua Bay (known as the largest on Oahu prior to it being filled for housing development), and Kāneohe Bay on Oahu, and along nearly the entire south shore of Molokai. Few remain today, although Molokai offers the best opportunities to view a Hawaiian loko.

Three different styles of fish ponds are being reconstructed at the Kaloko-Honokōhau National Historical Park on the Big Island of Hawaii. The non-profit Aoao O Na Loko Ia O Maui is restoring Kalepolepo Fishpond also known as Koie - i.e. in Kīhei on Maui - using a mixture of volunteers and skilled stonemasons. On Oahu, the private non-profit organization Paepae o Heeia ("Threshold of Heʻeia") is rehabilitating the roughly 600-to–800-year-old Heeia Fishpond, which is a walled (kuapa-style) enclosure in Heʻeia covering 88 acre of brackish water. The Kāneiolouma Complex, an ancient village on the south shore of the island of Kauai, has a fishpond within the 13 acre that includes taro patches, heiau, and a makahiki sporting arena.

These fishponds have been found to increase overall fish stocks in nearby waters, serving as a nursery that protects fish from predators.