Alberto J.P. Nunes

Size-related feeding and gastric evacuation measurements for the Southern brown shrimp Penaeus subtilis

Studies attempting to optimise feeding methods in penaeid aquaculture have often relied on results of growth, survival performance and food conversion ratios. At present, data relating to maximum ration, ingestion rates (IRs), faecal production rates (FPs), foregut evacuation and appetite revival are lacking for Penaeus spp. despite their relevance to the development of models aimed at maximising food use in shrimp culture systems. Size-related feeding and gastric evacuation (GE) measurements were determined for Penaeus subtilis by conducting laboratory-based feeding trials on individual animals. A total of 3482 samples of feed and (or) faeces were collected for quantitative analysis derived from 307 shrimp. Food ingestion was a function of shrimp body weight (BW). Feeding intensity increased progressively with shrimp size, but inversely in percentage terms, resulting in a larger faecal production per BW for smaller shrimp. On average, P. subtilis food ingestion was equivalent to 2.3% of its BW per hour, but consumption in shrimp with empty stomachs reached 4.9% BW/h. Foregut clearance rates (13%) peaked 3 h after food recovery, with the bulk of faeces being produced within 1 h. Food load occurred progressively as more feed was given and evacuated from shrimp stomachs, while feeding continued at reduced levels. Data indicated that control of feeding intensity and resumption of food intake by P. subtilis were not markedly affected by the level of their stomach fullness or by longer food administration intervals. The daily administration of food in shorter feeding intervals, although at continually reduced amounts, may be advantageous in the culture of P. subtilis.

Effects of the Southern brown shrimp, Penaeus subtilis, predation and artificial feeding on the population dynamics of benthic polychaetes in tropical pond enclosures

In less intensive shrimp culture systems, polychaetes are known to be a major food item of several penaeid species. Under these conditions, very little is known about their population dynamics and the possible interactions with penaeid predation and artificial feeding. This work examined the effects of Penaeus subtilis, predation, stocking density and supplemental feeding on the population dynamics of polychaetes in pond enclosures. The work was conducted in a shrimp pond, where forty-five 9-m2 open-bottom enclosures were built. The study consisted of four treatments: enclosures with feed and shrimp (i.e., FS); enclosures without feed and shrimp (NFNS, control); enclosures with shrimp and no feed (NFS); and, enclosures with feed, but no shrimp (FNS). For enclosures with shrimp, four initial shrimp stocking densities were used (i.e., 5, 10, 15 and 20 shrimp/m2). Benthic polychaetes were collected 2 days prior to shrimp stocking and were sampled every 10 days over the complete rearing cycle. A total of 1,631 substrate samples of 20.43 cm2 containing 20,283 polychaetes were collected for analysis. Overall, polychaete density and dry biomass over the production cycle varied from 956 to 11,921 polychaetes/m2 and 1.17 to 2.58 g/m2, respectively. Six polychaete families were identified and ranked relative to their numerical occurrence and frequency (Cn) as follows: (1) Spionidae (Cn=52.3%), (2) Capitellidae (Cn=37.9%), (3) Eunicidae (Cn=6.8%), and (4) Nereidae (Cn=2.7%), Pilargidae (Cn=0.3%) and Sabellidae (Cn<0.1%). P. subtilis final body weight varied from a minimum of 4.2 g to a maximum of 9.3 g, with final survival ranging from 42 to 69%. Shrimp predatory pressure produced a reduced polychaete growth in NFS and FS enclosures when compared to other treatments. Polychaete numerical abundance and biomass were greatly affected by higher shrimp stocking densities, while their population patterns appeared to be governed by other environmental and endogenous cues. Artificial feeding promoted higher polychaete levels even when shrimp were present, but it was not effective in alleviating P. subtilis grazing pressure at increased stocking densities (i.e., 15 and 20 shrimp/m2). Results showed that P. subtilis predation, shrimp stocking density and external food supply are major factors to be considered when establishing sustainable limits for polychaete use as a naturally occurring food source in aquaculture systems.

Food handling efficiency and particle size selectivity by the southern brown shrimp penaeus subtilis fed a dry pelleted feed

This study investigated the feed handling efficiency and size selectivity of four size groups of Penaeus subtilis fed three commercial feed particle sizes. Shrimp feeding behaviour was recorded with a video‐camera, installed below a glass aquarium, where one shrimp at a time was introduced and allowed to feed. A total of 163 specimens of P. subtilis were examined. Results indicated that over 59% of all food particles placed in the mouth by shrimp were completely or partially consumed, regardless of size. Large pellets however were less preferred than small ones. Manipulation capacity and capture success were also greater when shrimp were fed small particles. Shrimp size had no significant effect on manipulation efficiency, indicating that within the feed size range examined, food handling by juvenile shrimp was as efficient as adults. These results suggest that in aquaculture systems, the use of crumbles and broken pellets may be preferable to large pellets.

Bioavailability of crude protein and lipid from biofloc meals produced in an activated sludge system for white shrimp, Litopenaeus vannamei

The present study compared the bioavailability of crude protein and lipid from biofloc meals generated with an activated sludge system using two water sources: wastewater from shrimp experimental culture (BFL-W) and, artificially, using clean seawater (BFL-C). The sludge system operated by chemical and organic fertilization three times per week. Sampling of bioflocs occurred every two days during 81 days. To evaluate digestibility, each type of biofloc meal was incorporated into a reference diet (REF) at 300 g/kg. Another diet acted as a negative control (NEG) by using fish waste meal. The apparent digestibility of bioflocs was estimated by the indirect method using chromic oxide (Cr2O3) as the inert marker at 10 g/kg of the diet. Juvenile L. vannamei of 5.09±0.79 g (n = 440) were stocked at 10 shrimp/tank in 44 tanks of 61 L each that operated under a water recirculating regime. Biofloc meals contained a high ash content (591.0-649.2 g/kg) combined with a low crude protein content (95.9-137.3 g/kg). After 26 days, shrimp achieved a final survival of 93.2±0.8% and a biomass gain of 37.1±1.8 g/tank. Final shrimp body weight ranged from 9.01±0.15 to 9.45±0.13 g. The apparent digestibility coefficient (ADC) of crude protein in the biofloc produced from BFL-W, BFL-C and fish waste meal (NEG) reached 26.0, 25.7, and 64.1%, respectively. Similarly, the lipid ADC was 78.9, 67.9, and 85.8%, respectively. This study indicated that biofloc meals had a low protein availability for L. vannamei. However, although low levels of lipid were present, it proved to be available for the species. The dietary inclusion of biofloc meal appears to have a growth-promoting effect on shrimp, which may be associated with trace minerals, or other nutrients not identified in this study.