Use of rotifers-fed microalgal paste in the seed production of mangrove crab Scylla serrata in the Philippines

Despite the progress in the production of artificial diets for marine larvae, feeding during the early life stages of most aquaculture species still relies on live feeds such as rotifers. Advanced rotifer culture techniques are also available, however, in the Philippines, majority use batch cultures with fresh microalgae. These microalgae are prone to collapse resulting to inadequate supply of food for the rotifers that are fed to the larvae. Mangrove crab is one of the economically important aquaculture species in the country where mass seed production requires sufficient and steady supply of rotifers. Thus, here we examined the possibility of substituting fresh culture of green microalgae Tetraselmis tetrathele (FA) with flocculated T. tetrathele paste (FP) and commercially available Tetraselmis sp. (CP) as feed for rotifers (Brachionus rotundiformis) in the seed production of mangrove crab. Rearing of larvae was done until crab instar 1 (DOC 24) where growth and survival were taken to evaluate the viability of rotifers-fed microalgal paste. It was observed that the growth index (FA–6.93 ± 0.07; FP–6.91 ± 0.07; CP–6.96 ± 0.05) was similar for all treatments (P > 0.05) at termination. Comparable survival rates were noted for FA and FP at 1.08 ± 0.59% and 3.21 ± 2.09%, respectively (P > 0.05) while a significantly higher survival (P < 0.05) was recorded for CP at 7.73 ± 1.90%. These findings suggest that the algal paste tested are potential alternatives to fresh microalgae and this technique could benefit hatchery operators who lack the capital for setting up the facility and technical skills to maintain microalgae production.This research project was carried out with the support of SEAFDEC/AQD (study code NR-02-C2018T). The authors greatly appreciate the assistance of Phycology laboratory and Crab hatchery staff in the production of algae and rotifers, and in the larval rearing experiments, respectively

Grazing periodicity, grazing rate, feeding preference, and gut examination of early juveniles of abalone Haliotis asinina–fed five benthic diatom species

This study evaluated the suitability of five diatom species (Amphora sp., Cocconeis sp., Navicula ramosissima, Nitzschia sp., and Tryblionella sp.) as food to abalone Haliotis asinina early juveniles (5-mm shell length). Grazing periodicity, grazing rate, and feeding preference were measured; at the same time, abalone gut content was examined. Grazing incidence appeared to be continuous with significantly higher grazing intensity observed at nighttime from 6 p.m. to 10 p.m. (79%) than at daytime from 10 a.m. to 2 p.m. (40%) (p  0.05). Broken cells of Amphora sp. (22%) were significantly higher in the gut of H. asinina compared to Cocconeis sp. (2.8%), N. ramosissima, (1.8%), and Tryblionella sp. (0.2%) although the abundance of Nitzschia sp. (6%) was not significantly different from Amphora sp. (p > 0.05). Early juveniles showed significant preference for Cocconeis sp. (18.6%), followed by Nitzschia sp. (16.2%), N. ramosissima (13.9%), and Amphora sp. (13.4%), with the least preference for Tryblionella sp. (7.8%). Survival of H. asinina was similar in 4 diatom species (46–71%) except in Tryblionella sp. (8–12%). These findings suggest that diatom species Cocconeis sp., Nitzschia sp., Amphora sp., and N. ramosissima are the suitable live food for H. asinina early juveniles. Knowledge from this study would contribute to the development of a feeding protocol that would maximize production of H. asinina early juveniles in the hatchery.The Department of Science and Technology—Philippine Council for Agriculture and the Natural Resources Research and Development funded this study under the National Abalone Program of the Philippines, project on refinement of hatchery technology for the donkey’s ear abalone (Study code: NR04-M2009T), with the Aquaculture Department of the Southeast Asian Fisheries Development (SEAFDEC/AQD) as implementing agency

Production, feeding and storage of diatom Chaetoceros calcitrans paste by electrolytic flocculation with reduced Pb content

An innovative microalgae harvesting technique was carried out under various anode/cathode (2/2, 4/4 and 6/6) configuration and at different voltage treatment (3, 6 and 10 V) to efficiently electroflocculate Chaetoceros calcitrans. This study was conducted to determine the optimal configuration of electrode units (Pb and Al) and voltage settings that could improve the quality of harvested paste in terms of nutritional value and metal contamination for its later use in aquaculture. The use of 6/6 electrodes achieved the shortest harvest time of 48 ± 1 min and the lowest Pb content (83.7 ± 0.3 ppm). In terms of voltage treatment, harvest time was inversely proportional to the voltage used. However, Pb content was significantly lowest in the paste produced using 3 V (41.78 ± 0.12 ppm), when compared to those harvested under 6 V (304.35 ± 0.79 ppm) and 10 V (343.90 ± 0.91 ppm) treatment. Likewise, Pb residues in the resulting effluent are also lowest (0.245 ± 0 ppm) with 3 V treatments. C. calcitrans paste can be resuspended ≤6 months but with a lag phase of 3–4 days for use as starter culture. A 97% reduction in Pb content of C. calcitrans paste and 77% reduction in Pb content were obtained in Artemia (7.8%) fed C. calcitrans paste.This project was funded by the Aquaculture Department, Southeast Asian Fisheries Development Center (SEAFDEC/AQD) with Study Code Nr-01-Y2018T

Anti-luminous Vibrio factors associated with the ‘green water’ grow-out culture of the tiger shrimp Penaeus monodon

The ability of the “green water” grow-out culture of the tiger shrimp Penaeus monodon to prevent outbreaks of Luminous Vibriosis was investigated by screening associated isolates of bacteria, fungi, phytoplankton and fish skin mucus for anti-luminous Vibrio metabolites. Among the 85 bacterial isolates tested, 63 (74%) caused +∼+++ inhibition of the Vibrio harveyi pathogen after 24–48 h co-cultivation. The variation in growth inhibition rates of +, ++, and +++ were demonstrated by 15 (18%), 13 (15%), and 28 (33%) isolates, respectively, 24 h after treatment. Eight bacterial isolates showed consistently sustained maximum inhibition of luminous Vibrio after 24 to 48 h exposure. The majority of these luminous Vibrio inhibiting bacterial isolates were obtained from tilapia mucus and gut. In tests with fungi, 4 of 20 (20%) yeast isolates showed intracellular metabolites inhibitory to luminous Vibrio. Among filamentous fungi, 5 of 45 (11%) isolates yielded intracellular metabolites while 3 of 41 (7%) isolates had extracellular metabolites inhibitory to luminous Vibrio. These fungal isolates were identified as Rhodotorula sp., Saccharomyces sp., Candida sp., Penicillium sp., mycelia sterilia, and two unidentified species. The microalgae, Chaetoceros calcitrans and Nitzchia sp., consistently demonstrated complete inhibition of luminous Vibrio from 24 h and 48 h post exposure, respectively, and during the 7-day experiment. Leptolyngbia sp. caused a 94–100% reduction of the luminous Vibrio population from 104 to 101 cfu/ml 24 h post exposure which was sustained throughout the 10-day observation period. In contrast, the inhibitory effects of Skeletonema costatum on luminous Vibrio was bacteriostatic throughout the 7-day exposure while Nannochlorum sp. did not significantly inhibit luminous Vibrio. The skin mucus of jewel tilapia, Tilapia hornorum, had no resident luminous bacteria and inhibited this bacterial pathogen in 6–48 h, which was proportionate to the 103 and 105 cfu/ml test concentrations of luminous Vibrio. This study provides a scientific explanation that the effectiveness of the “green water” culture of tiger shrimp (P. monodon) in preventing outbreaks of luminous Vibriosis among P. monodon juveniles in grow-out ponds can be attributed to the presence of anti-luminous Vibrio factors in the bacterial, fungal, phytoplankton microbiota and the skin mucus of tilapia associated with this novel technique of shrimp culture.Appreciation is due to SEAFDEC-AQD and the Japanese Trust Fund Fish Disease Project for funding support. We also thank Drs. Yasuo Inui and Kazuya Nagasawa for encouragement and guidance, Dr. Leobert de la Peña for the Vibrio harveyi isolate, Deogracias Reyes, Jr. for the algal cultures, Catherine Lago for assisting in some experiments, and F. Y. Domingo for access to his jewel tilapia

Production, feeding and storage of Tetraselmis tetrathele paste by electrolytic flocculation

An innovative microalgae harvesting technique using electroflocculation was carried out at different voltage treatments (4, 7, and 9 V) using a fabricated voltage regulator and compared with harvesting by electroflocculation at 12 V using a car battery to efficiently electroflocculate Tetraselmis tetrathele. This study was conducted to determine the ideal voltage settings that could improve the quality of harvested paste in terms of nutritional value and metal contamination for its later use in aquaculture. The use of 7 V achieved low Pb content producing the best harvest biomass (1.4 kg, 87 min) which is comparable to the harvest biomass (1.7 kg, 68 min) using a 12 V car battery. Storage of T. tetrathele paste is best done in a chiller (2 ± 1 °C) rather than a freezer (-20 ± -4 °C) for ease in reactivation and maintaining higher cell viability for later use as a starter in aquaculture. Storage in a chiller allows T. tetrathele paste to be resuspended after six months and used as a starter culture.This study was funded by the Aquaculture Department, Southeast Asian Fisheries Development Center (SEAFDEC/AQD) Study code: Nr-01-Y2018T

Microalgal paste production of the diatom Chaetoceros calcitrans using electrolytic flocculation method at optimum culture conditions

The optimum culture conditions of the local strain Chaetoceros calcitrans were determined to improve biomass and reduce cost of production. Under outdoor culture conditions, higher cell density was attained when the cultures were enriched with Tungkang Marine Research Laboratory (TMRL) medium composed of cheap technical grade reagents and cultured at 25 g L−1 salinity. The cultures were lighted with two 40 W cool-white GE fluorescent tubes (24–35 μmol photon m−2 s−1). Using semi-continuous culture system under established optimum culture conditions, C. calcitrans can be re-cultured thrice and concentrated at each culture cycle using electrolytic flocculation method to produce 4.6 kg m−3 of diatom paste. The viability of concentrated C. calcitrans after 3 months of storage was comparable to live diatom cells. Simple preservation technique by low-temperature storage is convenient for storing algal concentrates for use as starter cultures and for feeding invertebrates. The paste costs USD 8.24 kg−1 inclusive of the assets and flocculation materials for culturing and harvesting the diatom, respectively. This study established the suitable conditions for mass culture of C. calcitrans and produced concentrated diatoms in paste form that is readily available for aquaculture hatcheries at a lower cost.This study was funded by the Aquaculture Department, Southeast Asian Fisheries Development Center (SEAFDEC/AQD) Code 5103-20T and Department of Science and Technology (DOST) under the auspices of the Philippine Council for Agriculture, Forestry and Natural Resources Research and Development (PCAARRD). The methods of this study were based on the results of the research code NR-02-C2005T funded by SEAFDEC/AQD