Abstract:
In the wild, green mandarinfish, Synchiropus splendidus, feed principally on a range of zooplankton, however, rearing zooplankton under captive conditions remains problematic. While Artemia are used intensively in aquaculture for rearing finfish, they have the benefit of being fast growing and readily available and therefore may serve as an alternative live feed for S. splendidus, however, the right size and density of Artemia to present to the fish needs to be determined. In addition, Replacement of live feeds with artificial diet remains investigation. The current experiment set to determine what stages and density of Artemia were appropriate for maintaining growth, leading to successful spawning events. To investigate this, a 4×3 completely randomised design (CRD) was used to test various live Artemia diets presented to the F1 progeny of green mandarinfish reared under artificial conditions. The experimental treatments were: 1) live adult Artemia fed at 3 individuals (ind) L-1; 2) newly hatched (NH) Artemia fed at 0.5 ind. ml-1; 3) adult Artemia at 2 ind. L-1 plus NH at 0.25 ind. ml-1; and, 4) adult Artemia at 1 ind. L-1 plus NH at 0.25 ind. ml-1. The Artemia used in all treatments, were fed on a daily diet of dry Spirulina platensis prior to enrichment with a mixture of live algae, i.e., either Tetraselmis gracilis and Isochrysis galbana or T. gracilis and Nanochrolopsis oculata. The initial, 1.2 year old S. splendidus used for the experimental trials, were raised in 45 × 120 × 50 cm glass tanks containing 270 l of 32-34 ppt seawater. The experimental tanks were separated into 2 parts; rearing (180 l) and egg collecting areas (90 l). After 8 months of feeding the fish the experimental diets twice per day, there were no significant differences (p0.05) in the growth performances when same sex fish were compared between treatments; male were always of a larger size. Only a single pair of S. splendidus fed on the adult Artemia began to display breeding behaviour when they were aged 1.7 years old and just three months before the termination of the trial. This pair of fish went onto successfully to spawn multiple times. This result, although observed for only this single pair of fish, leads to the assumption that the size and age at which S. splendidus reaches maturity under aquaculture conditions is when male fish reach 5.54 cm in total length (TL) and females reach 5.39 cm TL. The number of eggs in each batch of eggs that were laid ranged from 48 253 eggs. The study found that there appears to be an improvement in egg quality with each successive batch of eggs that are produced irrespective of the number of eggs produced in a batch. After hatching, the pro-larvae were transparent associated with large yolk sac and had undeveloped eye pigment and lacked a mouth. The digestive system was seen as a simple straight tube. In the second trial, various live Artemia and artificial diets will be fed on the green mandarinfish progeny (F1) and the effect on their reproduction will be investigated.