The effects of early weaning on the behaviour, growth and survival of Atlantic cod (Gadus morhua) and fat snook (Centropomus parallelus) larvae

Alves, Tarcisio (2003) The effects of early weaning on the behaviour, growth and survival of Atlantic cod (Gadus morhua) and fat snook (Centropomus parallelus) larvae. Masters thesis, Memorial University of Newfoundland.

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Abstract

Live food production is one of the most costly activities during the intensive culture of the larval stages of marine fish. But the culture of marine fish larvae requires extensive use of live food to produce healthy larvae. However, the process of weaning larvae from a live to a dry diet results in loss of growth and increased in mortality. Combining live feed and manufactured diets (co-feeding) at an early developmental stage has been shown to improve growth and survival of larvae compared to the use of live feed only. Moreover, it helps to condition the larvae to more easily accept the manufactured diet when live feed is withdrawn, resulting in a shorter weaning period. -- In this thesis, I conducted weaning trial~ to improve the larviculture protocols of two marine species, the Atlantic Cod (Gadus morhua), a temperate marine species, and Fat Snook (Centropomus parallelus), a tropical marine fish. Several combinations of live and inert food were examined as feeding protocols, to determine the earliest point at which larvae of these species can be successfully weaned from Artemia onto a dry diet. -- Two weaning experiments were conducted with Atlantic cod larvae. In the first experiment, 25 day post hatch (DPH) larvae were assigned to one of four treatments using Artemia as live food for 3, 5, or 10 days and a treatment without Artemia (larvae co-fed with rotifers for 7 days). By 45 DPH, larvae reared with Artemia for 10 days had significantly (P<0.05) better growth, had the highest survival and ingested more dry food pellets compared to all other treatments. In the second experiment, three treatments were developed in which larvae were co-fed with dry diet and Artemia on 25, 30 and 35 DPH for 10 days. A fourth treatment was assigned as a control in which larvae were fed only Artemia. Weaning age did not significantly (P>0.05) affect either growth or survival of larvae. However, larvae in the control treatment were larger and had a significantly (P<0.05) higher frequency of Artemia ingestion. Results from both experiments indicate that Atlantic cod larvae can be completely weaned by 35 DPH. -- Feeding trials were conducted with fat snook larvae. Fat snook larvae of30 DPH were assigned to five feeding trials in which larvae received Artemia for 5, 10 and 15 days (co-fed with a locally prepared dry diet), Artemia for 10 days (co-fed with a commercial dry diet), and only Artemia (control treatment). Larval survival was not significantly affected (P>0.05) by treatment. Fat snook larvae were successfully weaned by 35 DPH, but larvae weaned by 40 DPH displayed higher growth rates and were significantly (P<0.05) larger by the end of the experiment. There were no significant differences in any growth parameter between larvae weaned by 40 and 45 DPH. However, comparisons between treatments using different dry diets revealed a significant difference (P<0.05) in the frequency of dry diet ingestion, although it did not influence the growth of larvae. -- The results of the present study will benefit the intensive culture of both species, sharpening the current larviculture protocols and lowering costs on its large scale production.

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