Can Ulva reticulata replace Gracilariopsis heteroclada as natural food for the abalone Haliotis asinina?

Abalone are among the most important fishery resources with high commercial values worldwide, with Haliotis asinina being the most in demand and widely studied species in the Philippines. Abalone culture in the country mainly depends on the red alga, Gracilariopsis heteroclada, as food for cultured stocks. This however, is not sustainable as this alga is also being farmed both for agar production and human consumption. Hence, other sources of natural food need to be explored for large-scale culture of abalone. This study investigated the viability of Ulva reticulata as food for abalone. This green alga is common in the intertidal zones of the Philippines but of no commercial value. H. asinina early juveniles (N = 60, shell length 2.12-3.07 cm, body weight 1.7-5.9 g) obtained from the Abalone Hatchery of SEAFDEC Aquaculture Department were randomly distributed (n = 10) in three replicate containers and fed with G. heteroclada and U. reticulata for 15 days. After 15 days, abalone fed with G. heteroclada were significantly larger and heavier (2.82 +/- 0.04 cm and 4.64 +/- 0.19 g) than those fed with U. reticulata (2.62 +/- 0.03 cm and 3.45 +/- 0.14 g). Abalone fed with U. reticulata also exhibited weakness, hardfoot, and easily detached from the walls of the culture containers. Based on these results, despite its availability in large quantities, U. reticulata could not be solely used as an alternative natural food to G. heteroclada for abalone culture. However, its potential as a partial substitute to G. heteroclada may be further examined.

Automated summary

Abalone, particularly the Haliotis asinina species, is an important and highly studied fishery resource in the Philippines. The traditional reliance on Gracilariopsis heteroclada as food for abalone is not sustainable, prompting the investigation of alternative food sources like Ulva reticulata. However, the study found that while Ulva reticulata is not a suitable sole substitute for Gracilariopsis heteroclada, its potential as a partial substitute warrants further exploration.