An evaluation of the feeding regime for larval mahimahi (Coryphaena hippurus Linnaeus 1758) and cobia (Rachycentron canadum Linnaeus 1766)

Abstract

A series of five trials were conducted with an aim to evaluate the effects of different feeding regimes on the growth performance and survival of mahimahi and cobia larvae. The five feeding regimes were (1) delayed first feeding to mahimahi larvae, (2) rotifer and probiotic inclusions in live feeding regimes as practiced by industry on mahimahi larvae, (3) delayed first feeding to cobia larvae (4) copepods, Artemia and probiotic inclusions in live feeding regimes on cobia larvae, and (5) early weaning of cobia larvae to microdiets.Delayed first feeding for 0, 1, 2, 3 days and totally starved mahimahi larvae as well as delayed first feeding for 0, 1, 2, 3, 4 days and totally starved cobia larvae significantly influenced (P<0.05) the first feeding response, growth performance and survival of mahimahi and cobia larvae. Mahimahi and cobia larvae withstood starvation and maintained their high first feeding response for 2 and 3 days, respectively, after the day the yolk-sac was exhausted (2 day post hatch (DPH)), but the first feeding response significantly decreased (P<0.05) at the later stages. Delayed first feeding negatively affected the larval survival of both mahimahi and cobia larvae after 7 and 6 DPH, respectively. Negative influences in both larval species were also found in the growth performances in terms of length, wet weight, specific growth rate length and weight (SGRL and SGRW), head height, width, eye diameter, mouth depth and mouth width after 7 DPH. However, no influence on mahimahi and cobia larvae was observed when these larvae were fed 0 and 1 day delayed first feeding, except in cobia larval survival after 9 DPH (P>0.05).Provision of rotifers, enriched Artemia, and the combination of rotifers and enriched Artemia as the first feeding and Sanolife Mic probiotics added to water did not influence (P>0.05) the growth performance (length, wet weight, SGRL and SGRW), body indices (Head weight index and dry matter content) and survival of mahimahi larvae during the first 28 DPH. At 28 DPH, the survival of mahimahi larvae was 4.3- 6.0%. Meanwhile, the length, wet weight, SGRL and SGRW were 25.2-26.7 mm, 170- 190 mg, 6.1-6.3% and 21.7-22.0%, respectively.Dietary copepods and copepods plus Maz-zal added to water resulted in significantly higher (P<0.05) survival of cobia larvae (4.7 and 4.3%, respectively) than dietary enriched and un-enriched Artemia supplementation (3.0 and 1.4%, respectively) at 37 DPH (P<0.05). The effect of copepods, enriched and un-enriched Artemia inclusions in live feeding regimes on the growth performance (length, wet weight, SGRL and SGRW) of cobia larvae were significantly different (P<0.05) based on the larval stages. For example, at 16 DPH the growth performance of cobia larvae fed copepods was higher than larvae fed enriched and un-enriched Artemia, but lower values were observed at 23 DPH. At the end of the trial (37 DPH), the lowest wet weight and SGRW were observed in cobia larvae fed un-enriched Artemia (1717 mg and 22.7%). There was no influence of probiotic inclusion on the survival of cobia larvae though the total Vibrio count in water was significantly reduced during the rearing period. Similarity, the length, wet weight, SGRL and SGRW of cobia larvae fed copepods and copepods plus probiotics added to water were similar at 35 DPH (87-90 mm, 2016-2204 mg, 8.4- 8.5% and 23.2-23.4%, respectively).Early weaning of cobia larvae to microdiets resulted in lower survival due to cannibalistic mortality, but higher growth performance was achieved. The survival of 30 DPH cobia larvae fed first microdiets at 16 DPH was 3.5% and significantly lower (P<0.05) than those of larvae fed first microdiets at 19 and 22 DPH (5.6 and 5.9%, respectively). In contrast, the growth performances (length, weight, SGRL and SGRW) of 30 DPH larvae given first microdiets at 16 DPH were significantly higher (P<0.05) than those of larvae given first microdiets at 19 and 22 DPH. Early weaning to microdiets at 16 DPH increased the cannibalistic mortality of cobia larvae in third and fourth weeks by around 200% than larvae fed first microdiets at 19 and 22 DPH. No significant difference (P>0.05) in the growth performance and survival were observed when cobia larvae were first provided microdiets at 19 and 22 DPH. In summary, later weaning of cobia larvae to microdiets (19 and 22 DPH) did not influence the growth and survival, and early provision of microdiets to cobia larvae (16 DPH) increased the growth performance but decreased the survival due to cannibalistic mortality.