Species diversification in aquaculture is an increasingly important risk mitigation strategy that enables practitioners to navigate changing global scenarios. Emperor (Family: Lethrinidae) are recreationally, commercially, and culturally important fish species critically under-represented in aquaculture production. In this paper, we build on current regional diversification initiatives involving Lethrinids by exploring the aquaculture potential of grass emperor, Lethrinus laticaudis.
Wild L. laticaudis broodfish were collected in November-December 2020 and acclimated in flow-through seawater systems. More than 240 volitional spawning events without hormone intervention were recorded between one month after capture and February 2023, yielding > 51 million fertilised eggs. Spawning occurred across a range of temperatures (21 – 28 oC), salinities (24 – 38 ppt) and photoperiods (11.5 – 14.7 h). Individual fish, water quality parameters, and lunar cycle were associated drivers of spawning.
Initial larval rearing trials were characterised by poor survival and behaviour, with one attempt in 2021 producing 219 post-metamorphic juveniles. In October 2022, an approach for the commercial larviculture of Lutjanids was successfully adapted, resulting in the production of 8400 juveniles by transfer to nursery systems (50 days post hatch, dph). Larval development (Figure 1) was similar to that described previously for L. nebulosus and L. lentjan. Survival percentage and spatial productivity (2.9 juveniles/L) were each up to 10 times greater than our larval rearing attempts for L. laticaudis and other attempts for Lethrinus spp., respectively. Growth modelling of 2021 and 2022 cohorts infer marketable size is attainable following 12 months in grow-out systems.
L. laticaudis is a prolific, serial batch-spawning fish producing larvae that can be reared using simple intensive approaches, putting the species within technical reach of practitioners. Future research on seed quality, nutrition, and parametrisation of nursery and growout systems is needed to confirm compatibility with commercial aquaculture settings.