An automated rearing chamber system for studies of shellfish feeding

aquacultural engineering ELSEVIER

Aquacultural

An automated

Engineering

17 (1998) 69-77

rearing chamber system for studies of shellfish feeding Barry C. Smith*, Gary H. Wikfors

NOAA, National Marine Fisheries Service, Northeast Fisheries Science Center; Milford Laboratory 212 Rogers Avenue, Milford, CT 06460, U.S.A.

Received 29 January 1997; accepted 18 July 1997

Abstract Producing large volumes of high quality microalgae to feed shellfish and other organisms is a limiting factor in the development of the aquaculture industry. Feeding regimes yielding the highest conversion efficiencies of algal feed to molluscan growth are required to maximize the return on algal-culture investments. In the past we have used 12 specialized, manually-controlled molluscan rearing chambers to study nutritional requirements and growth of oysters, clams, and scallops. A computer-controlled, solenoid-valve system was added to automate seawater flow, volume of microalgal food delivered, and feeding duration independently for each chamber. Labor was reduced from 7 h per week to 3 h, while adding flexibility. Each chamber represents a model for a programmed nursery system. Evidence that superior growth of bivalves can be achieved by feeding regimes made possible by this apparatus are provided by an experiment with juvenile bay scallops (Argopecterz ir&ians). Published by Elsevier Science B.V. Keywords:

Shellfish; Nutrition; Aquaculture;

Automation

1. Introduction The nutrition of economically important bivalve mollusks is poorly understood. Cultured phytoplankton are used for rearing bivalve mollusks and other organisms at research and production scales. Incomplete development of artificial feeds (Coutteau and Sorgeloos, 1993) necessitates the use of live feeds. An obstacle to *Corresponding author. Tel.: + 1 203 7834289, fax: + 1 203 7834217; e-mail: barry.smith@:noaa.gov 0144~8609/98/$19.00Published by Elsevier Science B.V. All rights reserved PI1 SO144-8609(97)00015-0

the expansion of the aquaculture industry is incomplete knowledge needed to produce large amounts of high quality algal biomass economically (Coutteau and Sorgeloos, 1993). The ability to produce algae economically is only one consideration; algae produced must also be used as efficiently as possible. The optimal conversion of algal biomass to growth of the product organism is very important. (1) nutritional Gross conversion efficiency of feed encompasses two components: and (2) optimal consumption. quality of the algae for the product organism, digestion, and metabolic use of that algal food. The aquaculture industry, in its present form, is a fledgling endeavor. Agricultural livestock animals were ‘domesticated’ long ago. This long experience with animals such as cows. pigs, and sheep has led to detailed knowlcdgc of their nutritional requirements and proper feeding regimes. For example, Church (1991) contains a detailed listing of feeding standards for agricultural livestock; such information is published by the National Research Council, U.S.A. (NRC, 19X2). Ukeles and Wikfors (1982) developed a manually-operated system of 12 specialized rearing chambers to study questions of feed quality and quantity in mollusks, This system has served well for the qualitative study of shellfish nutritional rcquircments for the eastern oyster, Crassostrea virginica (Wikfors ct al.. 1996), and the northern quahog, Mercenaria mercenaria (Wikfors et al., 1992). To study the effects of different feeding schedules on mollusks, however, the ability to feed at different times around-the-clock was needed. A less labor-intcnsivc system than the man ually-operated one was designed to accomplish this, using process control and automation technology that was readily available. The juvenile bay scallop, Argopecten b-radians, was the tirst bivalve employed as the test organism in the initial experiments using the automated molluscan rearing chamber system described in this report. In bay scallop culture, the economic benefits of different feeding regimes arc largely unknown, although related scallop species have been studied (Martinez et al., 1995).

2. The manual system The original molluscan rearing chamber system was dcscribcd by Ukclcs ant: Wikfors (1982) and has had only minor alterations since then. The following is ;I description of the system before automation: seawater was provided from a running seawater system installed throughout the laboratory building. The ‘raw‘ seawater was filtered through a series of triplicate 20. IO. I. and 0.5 jtrn cartridge filters, passed through a final 0.5 pm ‘finishing’ filter and a UV unit. This filtered. UV-treated, seawater was piped into a head-tank where it was aerated and brought to experimental temperature (25°C) with thermal controllers and two 1000 W glass immersion heaters. The seawater was gravity-fed from the head-tank (1 .O m drop) to a 16valve manifold which supplied each of the I2 chambers (0.15 m drop) through 0.63 cm diameter silicone tubing (see Fig. 1 for general representation). Each chamber consisted of a 38.1 cm long by 16.5 cm diameter PVC schedule-80 pipe cut in half down its length. Semi-circular inserts in the ends of each piece oi

B. C. Smith, G. H. WikforslAquaculturul

Engineering 17 (I 998) 69- 77

TWO THERMAL REGULATORS

WATER TABLE WITH DMIN Fig. I.

Diagrammatic

representation

of the automated

molluscan

rearing

chamber

system

pipe-half formed the chamber (see Fig. 2 for basic structure). A 1 mm mesh screen in a PVC frame fitted between the pipe halves with weather stripping to make a watertight seal. Fifty juvenile shellfish were placed on this screen during experiments. A second basket-shaped screen was added beneath the original screen for experiments with scallops. The scallops were placed between these screens to prevent them from attaching, by byssal threads, to the chamber interior. ‘The chamber halves were clamped together with two large hose clamps and supported on a stand. All twelve such assemblies were placed in a water table. The filtered and UV-treated seawater ran through two ball valves into the top of each individual chamber at one end. The first ball valve was used to control rate of flow, which could be calibrated at the start of each experiment and adjusted as needed. The second ball valve was used to turn the flow on and off. Seawater flowed out of the chamber through an overflow pipe fitted to the bottom of the opposite end of the chamber. With this arrangement, the water continuously flowed past the shellfish on the screen and then out of the chamber. When a feeding period was started, the seawater was shut off and the chamber was drained through a ball valve on the bottom of the chamber. A measured volume of algal culture was added through a funnel at the top of the chamber, and the chamber was refilled with seawater. The animals were allowed to feed for 4 h with no seawater flow. At the end of the feeding period, the seawater flow for each chamber was resumed, and flow-rate was adjusted. Feedings were generally conducted every working day, five days per week. Every seventh day, the animals were removed, and shell height, live weight, and volume displacement were measured.

I?

R. C. Smith. G. H. WikforslAquuculturui Engineering I7 (199X) 6% 77

SEAWATER (NO) INFLOW VALVE

VALVE CONTROL, VIA COMPUTER

\

CHAMBER -_ BO?lOH HALF

OUTFLOW & WATER LEVEL CONTROL PIPE Fig. 2. Individual rearing chamber. The chamber valve ‘NO’ = normally open, ‘NC’ = normally closed.

k 3X.1 cm Ion,li ami IC,.i cm dlanietcr.

Nutrition requiring

manner

experiments conducted in this over an hour of staff time daily.

have

lasted

Solenoid

up to 24 weeks.

3. Automation To automate the molluscan rearing chamber system, the seawater feed system, the structure of the chambers, and their general arrangement were not modified significantly. Fig. 1 depicts the system in its current, automated configuration. Electronic valves controlled by a personal computer. have replaced manual valves to control feeding, draining and seawater flow. The control software selected was Labview (National Instruments, Austin, TX). a visually-oriented programming and control package installed on a 486, 33 MH7 computer. The software was programmed to control a 100 pin board with 96 digital In/Out pins (PC-DIO-96, National Instruments, Austin, TX). Each pin was configured to put out 5 V direct current (5 VDC) when required. This voltage controlled a relay, sets of four of which were plugged into a mounting board (Relay; CX240D5R, board; PB4P, Crydom Company, Long Beach, CA), used to actuate a 12 V alternating current (12 VAC) solenoid valve with a 3. IX mm oriticc (Burkert, Orange, CA. See below for part numbers). Each chamber assembly

B. C. Smith, G. H. WikforslAquacultural Engineeting 17 (1998) 69- 77

73

included three valves: seawater, algal feed, and drain. All 36 valves had PVC schedule-SO bodies, Viton diaphragms, and were rated for submerged operation. They were attached to the chambers with PVC close nipples. The 12 VAC current was stepped down from regular 120 V service with transformers (T-1-81050, Acme Electric, Lumberton, NC). All 12 seawater-feed solenoid valves were three-way with one-way normally open (# 124-F-l/8-F-PP-1/4-12/60-08-0-F-000, Biirkert, Orange, CA). Using this configuration, no current was drawn during normal flow, and an air vent is opened when the seawater flow is stopped. All the other solenoid valves - 12 drain valves and 12 algal feeding valves - were two-way, normally closed valves (# 124-Al/8-F-PP-1/4-12/60-08-0-F-000, Biirkert, Orange, CA). Again, no current was drawn most of the time, saving electricity and reducing valve wear. Each computercontrolled solenoid valve replaced a manually-operated ball-valve (Fig. 2). Further, the algal-feeding-funnel was replaced with a 4 1 aspirator bottle and a length of silicone tubing. Gentle aeration, from air stones (# 12520, Lee’s Aquarium Products, San Marcos, CA), was used in these jars to keep the microalgae in even suspension. The air had first been filtered through a Millex-HV 0.45 pm filter unit (# SLHV025NS, Millipore Corp, Bedford, MA). No suitable 5 VDC valves were found and no suitable circuit boards were found that would put out more voltage; therefore, relays were necessary. Twelve VAC was the lowest voltage found for the required valve and was selected for safety purposes - minimizing the risk of injury from shock. Further, each valve circuit was protected with a 3 A fast-blow fuse. If all components had been available in the same voltage, the relays would not have been needed and the circuits could have begun and ended at the circuit board. This would have allowed verification of valve operation by monitoring the integrity of the circuit through the valve. A 96 pin I/O board was selected of which 36 pins have been used; the remaining pins are available for expansion and modification. The next smaller board available had 24 pins at about 66% of the cost. Future modifications will replace bubble-mixing with a stir-plate beneath each of the algal feed jars for more thorough and uniform mixing. A thirteenth chamber will also be added to allow four triplicate tests and an unfed control to be conducted simultaneously.

4. Normal operation The three valves on each of the 12 chambers can be operated independently of all others. It is possible to operate less than 12 chambers in an experiment and to operate each of them on individual schedules. Feeding interval, feeding duration, and the amount of algae for each chamber are entered into a table displayed on the computer’s monitor screen. Once started, the system repeats the programmed feeding sequences until stopped. Most of the time the system will be in ‘normal running mode’ wherein seawater flows through the chambers, and all the valves are off. When it is time to feed the

shellfish, ‘draining mode‘ begins. During this phase. the seawater valve closes to stop the seawater flow, and the drain valve opens to drain a prescribed volume from the chamber. The volume drained from the chamber is then replaced partially when the algal-feed valve opens for a timed interval. The algal valve then closes and the seawater valve opens for the time required to till the chamber. Feeding mode then begins for a pre-determined time period. during which the seawater valve is the only valve operating (i.e. drawing current). When the shclltish have fed for the programmed time, current to the scawatcr valve is shut off. it opens, and ‘normal running mode’ is resumed until the next feeding period.

5. Testing by experiment The system was calibrated with a 100 ml graduated cylinder and stopwatch to measure the actual flow through each valve at the beginning of each experiment. These values, in ml s ‘, were then used to calculate the time each valve had tcl open in order to deliver the required volume of liquid. These times were input to the software, which the manufacturer maintains is accurate to 50 ms, to opcratc the valves. Algal cultures for feeding were grown in the Milford Laboratory’s scmicontinuous mass algal culture system (Ukeles, 1973) under bacteria-free conditions. The algal food culture used in this experiment was ~T&mehis clzui strain PLY 429. The first experiment conducted with the automated system was deslgned to text the effect of four different feeding regimes on the growth of juvenile scallops. Four individual chambers were programmed to feed cvcry 3. 6, 12. or 24 h, each of which was fed at noon. with the multiple feedings separated uniformly over 24 h In these treatments the total feeding time and food volume per day were the same for all experimental regimes (Table 1) but the number of times the food was administered was different between treatments. The food volume. or daily ration. was 0.012 ml packed algal cells per animal per day. A fifth chamber served as arl unfed control. following the flow cycle of the 3 h feeding rcgimc but without an!

Table

I

Experimental

chamber

four fed treatments.

system feeding regimes.

The first treatment

Feeding

Feed

interval (h)

duration

(h)

Note

that teed quantity

per da> ~a\

the SUIIC in the

was an unfed control Feed quantityiintcrval

l~eed quantity:da)

(ml packed cells/

(ml packed aells,

scallop/feeding)

scallop;day)

B. C. Smith, G. H. WikforsiAquacultural

Engineering I7 (I 998) 69- 77

15

algal food added. The remaining seven chambers were devoted to testing opentank cultured algal diets, the results of which will be reported elsewhere. Groups of 50 juvenile scallops were placed between the screens in each of the 12 chambers. Scallops averaged 38.8 Ifr0.6 rng, live weight each, at the start of the experiment. Animals were removed from the chambers every seventh day between feedings, and live weight was measured.

6. Results and discussion The valve-control system performed dependably, delivering measured rations of algal food within 3% accuracy except chamber 11 which had a sample variance of 4.9. It is suspected that this level of error was due to the measuring method which. using a 100 ml graduated cylinder, becomes less accurate above a 100 ml volume (see Table 2 for calibration data). Differing flow rates between algal valves was mainly attributable to variations in the size of the tubulation on each aspirator bottle. No component malfunctions or failures occurred during this experiment. More operating time is needed to test the durability of the system. Survival of scallops in all fed chambers was good; no more than three animals died per chamber (94% survival) except in the unfed control which had a 66% survival through week 4 and then complete mortality by the end of the next week., with no growth. Scallops fed every 6 h had growth rates superior to those fed at the other time intervals tested (ANOVA, P = 0.0194). Scallops fed every 6 h averaged an 11.8% increase in weight per day while scallops fed every 3 h increased 9.8% per day. Scallops fed every 12 h had an average weight increase of 6.3% per day and scallops fed once per day increased an average of 2.3% per day. This suggests that a significant increase in growth can be achieved by splitting the daily algal ration into four equal feedings per day instead of one. A nursery system could benefit with no expansion in algal production, but merely modifying the feeding schedule. Automating the chambers not only allowed the ability to feed on experimentally-varied schedules, continuously, but also reduced labor time considerably

Table 2 Experimental chamber valve in 10 s

system calibration

data.

Volume

of algal food flowing through

each algal feed

Chamber

1

2

3

4

5

6

7

8

9

10

II

12

Volume

89 89 88 91

87 87 87 89

8Y 89 89 91

84 84 84 86

91 92 91 93

89 90 90 90

80 79 81

80 80 80 81

99 96 97 96

81 81 81 83

100 101 101 105

01 ‘IO 90 92

Mean

89.25

87.5

X9.5

84.5

91.75

89.75

80

80.25

97

81.5

101.8

90:75

I

1

1

0.92

0.25

I

0.25

2

4.9

0.02

Sample variance

1.58

I

compared to the manual once-per-day, five-days-per-week feeding regime. A 57% time (labor) savings was calculated, indicating that operating costs can be greatly reduced by automating a shellfish rearing system. The majority of the labor savings was experienced in the way the algal food was delivered. With the manual system. one had to measure and deliver the algae to each chamber as well as stop and start the water flow before and after every feeding. This required a minimum of 5 h per week. With the automated system, the aspirator bottle can hold over a weeks supply of algae which is distributed by the control system. Thus, one need only attend to the chambers once a week for an hour or less. The filtration system, which was not modified, requires an avcragc of 2 h per week for cleaning. Other, researchers have observed benefits when adding technological advancements to culture systems (Kanamaki and Shirojo, 1994; Lee, 1994). Electrical power consumption increased less than 776 W. The solenoid valves operate at 1.5 W and, with the operating sequence described, no mom than 24 valves operated at a time and for no more than 100 s. Only I2 valves, the water flow valves, operated up to 4 h at a time during the feeding period. The valves were off between feedings. The twelve variable speed stir plates used a maximum of 18 W each and were set at 10% of maximum speed. The personal computer was equipped with a standard 200 W power supply which supplied the computer, monitor, circuit board, and relays. The manual system used a total of 2077 W, having two 2000 W heaters and a 77 W UV lamp. This brings the total energy usage to less than 2853 W at any time for the automated system. Each chamber can be considered a small version of a shellfish rearing system. Process-control of production-scale rearing systems may be similar to this experimental model especially when retrofitting existing manual systems where the operating variables, for the particular system, are already known. All components of the system described here are readily available. The total cost of automating this research system, including the purchase of the personal computer, software, and all components, was $11550.90. Computer control is necessary for experimental replication at a high level of precision, but simplified timers could he used with electronic valves in a commercial nursery at considerably lower cost. There are a great number of options, ranging from low cost light timers (about $20.00 and up) to computer-programmed process control (about $2000.00 and up). with which commercial hatcheries could realize the benefits of optimized, automated feeding of shellfish.

Acknowledgements This project was funded partially by a collaborative agreement with the University of Connecticut, Marine Sciences and Technology Center. WC thank A,jit Gokhale of National Instruments, Austin, TX for software advice, Chris Vcnditti for AUTO-CAD drawings used in the figures, and Jennifer Alix and Mark Dixon for assistance with experiments. Mention of specific trade names does not imply endorsement by the National Marine Fisheries Service.

R. C. Smith, G. H. Wikfor~slAquaculturaIEngineering 17 (1998) 69- 77

77

References Church, D. C. (1991) Livestock Feeds and Feeding, 3rd edn. Prentice Hall, New Jersey. Coutteau, P. and Sorgeloos, P. 1993. Substitute diets for live algae in the intensive rearing of bivalve mollusks - a state of the art report. World Aquaculture, 24(2), 45-52. Kanamaki, S. and Shirojo, Y. 1994. Laborsaving systems and the technometric management of the rearing environment for the mass production of larval fish. Bulletin of the National Research Institute of Aquaculture, (Suppl. 1), 97-103. Lee, P. 1994. Computer automation and intelligent control for aquaculture. Bulletin of the National Research Institute Aquaculture, (Suppl. I), 105-110. Martinez, G., Caceres, L. A., Uribe, E. and Diaz, M. A. 1995. Effects of different feeding regimens on larval growth and the energy budget of the juvenile Chilean scallops Argopecten purpuratus Lamark. Aquaculture, 132(3/4), 313-323. NRC (1982) United Slates-Canadian Tables of Feed Composition, 3rd edn. National Academy Press. Washington, D. C. Available at the internet web site: www.nas.edu Ukeles, R. (1973) Continuous culture - a method for the production of unicellular algal foods. In Handbook of Phycological Methods. ed. J. R. Stein, pp. 233-254. Cambridge University Press, London. Ukeles, R. and Wikfors, G. H. 1982. Design, construction, and operation of a rearing chamber for spat of Crassostrea virginica (Gmelin). Journal of Shellfish Research, 2(l), 35-39. Wikfors, G. W., Ferris, G. E. and Smith, B. C. 1992. The relationship between gross biochemical composition of cultured algal foods and growth of the hard clam Mercenaria mercenaria L.. Aquaculture, 108(1/),2 135-154. Wikfors, G. W., Patterson, G. W., Ghosh, P., Lewin, R. A., Smith, B. C. and Alix, J. H. 1996. Growth of post set oysters, Crassostrea virgirzica, on high-lipid strains of algal flagellates Tefraselmi~s spp. Aquaculture, 143(3/4), 411-419.