Nile tilapia belongs to the class of the ray-finned fishes, to the order of Perch-like fishes and to the family of Cichlids and is therefore a relative of many ornamental fishes. Its origin are lakes, inland and coastal rivers of middle Africa and Near East. Although it is regarded as potamodromous (wandering in fresh water only) it lives as well in brackish water and can even adapt to salt water.
The members of this species dwell at the surface or in depth to 6 or even 20 meters and prefer water temperatures between 16 and 29 °C. In the active part of their day they swim in shoals whereas they retire to rest preferably during the night.
Nile tilapia prefers complex habitats with muddy or sandy or gravel bottoms where it finds shelter from predators (including elder conspecifics) but can be found also in open waters. It feeds near the bottom on phytoplankton (algae etc.) and invertebrates mainly.
Adults measure between 20 and 60 cm and weigh between 130 g and over 4 kg. Nile tilapia can live for up to nine years of age but reach maturity at the age of only 3 to 7 months, being as small as 7 cm and as light as 16-17 g. Courtship lasts several hours, the male gently bites or nudges the female, swims in front of her and leads her to the spawning site, a nest in shallow water that he built in firm sand. Mouthbreeder: After fertilisation the female carries up to 240 eggs in her mouth during 7 to 18 days until the larvae hatch.
The species is very prolific and spawns several times a year. Because it has been easy to reproduce and to farm since the ancient Egyptians it has been introduced in many countries, including Southern Africa, Southeast Asia, USA or Mexico.
As males grow faster and bigger, male-only ponds have become an industry standard since the 1970s. Hatcheries deliver male-only juveniles produced by feeding sex hormones to the fry or by hybridization when crossbreeding various tilapia species or strains. Success is however not guaranteed. High stocking densities may negate the growth advantage, high temperatures may reverse the sex, and the growth of YY males may not differ from that of XY males. Further research is needed to clarify whether all-male populations display higher aggressiveness than mixed-sex ones. Any other impacts of mono-sex shoals on the animals have not yet been studied.
One advantage of Nile tilapia farming would be that the biology of the species does not require fish components in its feed. But if you have a look at the criteria of the leading labels for sustainable aquaculture you will learn that fish meal and fish oil plays a role as growth promoter also in the Nile tilapia farming industry. Fish components are not only expensive but ecologically questionable as they mainly originate from specialized forage fishery that requires one fourth to one third of the global catch. This is in contradiction to sustainability and impairs the marine food chain and consequently the living of marine animals, thus animal welfare. Not to mention the welfare of about 450-1000 milliard* fishes caught for feed annually. Moreover, feeding fish meal and fish oil to tilapia gives a bad example for the widespread small and extensive tilapia ponds run for local supply in Africa and Asia.
* Milliard in FishEthoBase = a thousand millions
Today, Nile tilapia with its various strains is the second most farmed fish species worldwide, due also to its easy to fillet body and its consumer friendly taste and texture.
It is all the more amazing that a species farmed for such a long time, in so many regions of the world and in such quantities does not seem to have adequate priority for ethological research.
Hence recommendations on fish welfare for farmers are still limited, but the few that are certain rather challenge common practice. For example Nile tilapia need individual access to daylight as well as to darkness and to opportunities for withdrawal. Instead they are in some cases even kept in covered tanks without any structure.
Welfare problems could also occur with the space provided to the fish with regards to the species' hierarchicals and territorial behaviour. In experiments males established linear hierarchy, but given enough space, they did not display dominance while each one established its own territory. In other experiments, fighting between males put into the same tank lasts until hierarchy is established (up to three days).
Nile tilapia are intelligent individuals able to learn. In small groups, they establish carefully arranged hierarchies within hours and stick to them, which is not possible without individual recognition of conspecifics. They may suffer under high density resulting in increased mortality and in turn benefit from decreased density by increased growth.
Nile tilapia are used to substrate like sand or mud for feeding and nest building. While mating, males look for sand for nest building as a choice experiment revealed, and individuals may benefit from substrate by increased growth, as another study evidenced. In most farming systems, however, substrate is not provided at all.
Nile tilapia display inter-individual differences in daily rhythms and in coping with novel situations and stress. Thus, negative effects of overall aquaculture conditions may differ individually and even increase in some individuals.
There is a protocol for humane slaughter of Nile tilapia available, but of the 4 to 16 milliard* individuals slaughtered every year, still only a minority is efficiently stunned. This means that many individuals may undergo severe pain before death occurs by exhaustion or by filleting alive.
For the time being, labels (i.e. seals of approval) are not helpful for clients who care for the welfare of farmed fish. The guidelines of organic labels are the ones most inclined to grant animal welfare, yet they define no tangible instructions. All other labels address animal health at best, but do not acknowledge all-encompassing aspects of animal welfare. That is to say that even fishes farmed under labels like organic, ASC, or Friend of the Sea, often live under the conditions of intensive animal husbandry. However there is some hope as several labels are currently studying the feasibility of integrating fish welfare into their certification schemes.
If we want to change the disregard for animal welfare, we need more of two things: ethological research and pressure from concerned consumers who want to eat respectfully-farmed fish.