Determining ingestion of microbound diet particles by mud crab, Scylla serrata, larvae

This study evaluated 14C-labelling as a tool to investigate the suitability of microbound diet (MBD) particles for the various larval stages of the mud crab, Scylla serrata. The results showed that S. serrata larvae held in seawater containing 14C leachate from 14C-labelled MBD particles (after MBD particles had been removed) did not contain levels of 14C above background. However, dead S. serrata larvae held in water with 14C-labelled MBD particles had a significantly higher 14C content than background even after thorough washing. They suggested that MBD particles trapped on the body of crab larvae cannot be completely washed off, and they represent a source of error that needs to be corrected when using this technique to determine ingestion of MBD particles by crab larvae. Consequently, a control treatment consisting of dead larvae held with 14C-labelled MBD particles was used to correct larval ingestion data in subsequent experiments. To determine larval ingestion of MBD particles, each larval stage of S. serrata was fed 14C-labelled MBD over a five-hour period and their radioactive contents were determined hourly. MBD particles were readily ingested by all larval stages of S. serrata. Ingestion of MBD particles increased with larval development with megalopa consuming more than three times the amount of MBD than Zoea V and more than ten times that of Zoea IV larvae. Ingestion of MBD particles by Zoea I declined after four hours, whereas ingestion by Zoea II, III and megalopa did not differ significantly over the five-hour feeding period. Zoea IV and V showed greater levels of MBD ingestion after four and five hours than after one hour. The present results suggest that the time to reach maximal ingestion, as indicated by the time to achieve maximum larval 14C content, for Zoea I, II, III and megalopa is one hour, but is greater for Zoea IV and V. The results of this study allow fine-tuning of a technique with great potential for investigating aspects of the nutrition of S. serrata larvae and indicate clear potential for developing successful MBD for them

Grow-out of the tiger shrimp Penaeus monodon in floating net cages in Batan Bay, northern Panay

The effects of two stocking densities and two feed combinations on growth, survival and production of the giant tiger shrimp Penaeus monodon in floating net cages were studied in an attempt to refine the existing technology on cage culture of tiger shrimp for the benefit of small- and medium-scale fish farmers. Four treatments were tested, replicated in time: stocking density of 100 shrimp/m2, feeding with 70% commercial shrimp pellets P and 30% 'trash fish' F; 100 shrimp/m2 and 50% P + 50% F; 200 shrimp/m2 and 70% P + 30% F; and 200 shrimp/m2 and 50% P + 50% F. Harvested after 93–95 d, the shrimps at the lower density treatments were significantly larger and had greater proportion of good sizes (>18 g body weight). Although the combination of 70% P + 30% F resulted in better growth, the combination of 50% P + 50% F resulted in more good-size shrimps. Survival, production, and gross income were not significantly different among treatments. None of the treatments in this study was economically viable. Gross income was very low due to poor growth and survival, mostly due to luminous vibriosis, then a new disease that eventually wiped out many shrimp hatcheries and ponds around Panay Island

Evaluation of partial replacement of live and fresh feeds with a formulated diet and the influence of weaning Panulirus ornatus phyllosomata onto a formulated diet during early ontogeny

We have evaluated the potential of a formulated diet as a replacement for live and fresh feeds for 7-day post-hatch Panulirus ornatus phyllosomata and also investigated the effect of conditioning phyllosomata for 14–21 days on live feeds prior to weaning onto a 100% formulated diet. In the first trial, the highest survival (>55%) was consistently shown by phyllosomata fed a diet consisting of a 50% combination of Artemia nauplii and 50% Greenshell mussel, followed by phyllosomata fed 50% Artemia nauplii and 50% formulated diet and, thirdly, by those receiving 100% Artemia nauplii. The second trial assessed the replacement of on-grown Artemia with proportions of formulated diet and Greenshell mussel that differed from those used in trial 1. Phyllosomata fed a 75% combination of formulated diet and 25% on-grown Artemia and 50% on-grown Artemia and 50% Greenshell mussel consistently showed the highest survival (>75%). Combinations of Greenshell mussel and formulated diet resulted in significantly (P < 0.05) reduced survival. In trial 3, phyllosomata were conditioned for 14, 18 or 21 days on Artemia nauplii prior to weaning onto a 100% formulated diet, which resulted in survival rates that were negatively related to the duration of feeding Artemia nauplii. In the final trial, phyllosomata were conditioned for 14 days on live on-grown Artemia prior to weaning onto one of three formulated diets (one diet with 44% CP and two diets with 50%). Phyllosomata fed a 44% CP diet consistently showed the highest survival (>35%) among all treatments, while those fed a 50%-squid CP diet showed a significant (P < 0.05) increase in mortality at day 24. The results of these trials demonstrate that hatcheries can potentially replace 75% of live on-grown Artemia with a formulated diet 7 days after hatch. The poor performance associated with feeding combinations of Greenshell mussel and formulated diet, and 100% formulated diet as well as conditioning phyllosomata for 14–21 days on live feeds prior to weaning onto a formulated diet highlights the importance of providing Artemia to stimulate feeding

Ontogeny of feeding apparatus and foregut of mud crab Scylla serrata Forsskål larvae

The development of the feeding apparatus of the mud crab Scylla serrata larvae was studied using electron microscopy for mandibles and light microscopy for other paired mouthparts and the foregut. The six paired mouthparts, which consisted of the mandibles, maxillules, maxillae, first maxillipeds, second maxillipeds and third maxillipeds, were dissected from specimens representing each larval stage. The first five paired appendages were already present in newly hatched larvae while third maxillipeds appeared only at the megalopa stage. Mandibles displayed complex incisor and molar processes at early zoeal stages, which became simple in morphology at megalopa. Mandibular palp buds were observed at the zoea 5 stage and these became fully developed as three-segmented mandibular palps at the megalopa stage. Endopods of other paired mouthparts exhibited increased number of setae and size as the individual metamorphosed from zoeal stages to megalopa and crab instar. The foregut appeared as a continuous cavity at zoea 1 where the cardiopyloric valve was indistinct while the filter gland was clearly identifiable. Zoea 2 and succeeding zoeal stages exhibited a setose foregut; the gastric mill and its lateral and median teeth were prominent at zoea 3 stage. The significance of these morphological changes is discussed in terms of its implication in larval feeding management