Project Goals
The project, Development of Polyculture Systems for the Production of
Juvenile Reef Fishes Suitable for Stock Enhancement, accomplished its
primary goal of testing an enriched culture environment for the production
of juvenile fish behaviorally suitable for the restoration of marine
fish stocks. This
involved development of polyculture systems for marine fish and habitat forming
species, specifically seagrass and oysters, and testing the hypothesis that
fish reared in polyculture were behaviorally better adapted for release in
the wild than fish reared in conventional monoculture.
1) The
construction of a new type of experimental facility at the CCFHR, a greenhouse
for the polyculture of plants and animals.
Major milestones included:
- Student training through the development of new cultured fishes
stocks and their experimental evaluation.
- Pilot scale replicated rearing trials with representative
species of two dominant reef fish families (Pigfish, Orthopristis
chrysoptera, Linnaeus, family Haemulidae and Black sea bass, Centropristis
striata, Linnaeus, family Serranidae). Trials compared growth
and survival of fishes reared in conventional monoculture and in polyculture
with associated habitat species.
The execution and analysis of experiments comparing behavioral
characteristics of juvenile grunts and sea bass reared in monoculture
and polyculture systems.
Project Background
Reef fish stocks are generally in poor condition throughout US waters
(NMFS 1999) and stocks of some grouper species ( Nassau grouper, Goliath
grouper) are so low that their harvest is prohibited in US waters by
law. Ault et al. (2001) concluded that the fishing mortality
rate for groupers in the Tortugas region was 2 to 10 times the exploitation
level that would achieve Maximum Sustainable Yield (MSY). Unfortunately
over fishing is not limited to groupers and “serial over fishing”, where
the largest species are removed first followed by smaller, less desirable
species (Ault et al, 1998), has proceeded to the extent that even some
grunt populations are chronically over fished. Although increased
fishery regulation and the creation of marine protected areas (MPA) should
alleviate chronic over fishing of many stocks, particular species and
particular regions may be slow to respond to conventional management
techniques.
One management alternative is the stocking of hatchery reared juveniles. It
is important to distinguish such cases into those where intensive stock
enhancement programs may be effective and those where a smaller scale
but focused effort seems more likely to succeed. Intensive stock
enhancement generally applies to widely distributed stocks of particular
economic and cultural importance such as red drum and striped bass, in
the US, and Japanese flounder and red sea bream in Japan. The importance
of such stocks has insured the development of systems that can support
massive stocking programs and the ability to saturate systems with hatchery
reared juveniles stocked primarily to enhance the fishery. In contrast,
for stocks of smaller size and limited geographic range that have been
overexploited to the extent that the fishery is no longer viable, systems
for mass production of juveniles are unlikely to have been developed
and availability of brood fish may be limiting. In such cases,
an alternative goal is to reestablish an adult group of sufficient size
and in a suitable location to allow natural reproduction and transport
processes to allow or speed the recovery of the species throughout the
system. In such a situation a more focused effort is required and
the emphasis shifted from the quantity of fish stocked to their genetic
variability, retention in the system and survival through the reproductive
stage. Of critical importance to this type of restoration program is
the behavioral and physiological quality of stocked fish as a variety
of studies have demonstrated that cultured fish exhibit behavioral deficits
linked to low survival after stocking (Brown and Laland, 2001).
It is with this situation in mind that we conducted polyculture studies
of reef fish species and depending on their juvenile habitat association,
oysters or sea grass. Comparative studies of fish monoculture and fish/habitat
species polyculture were conducted with two fish species from families
that play dominate roles in coral reef systems. The schooling grunts
(represented by the pig fish, Orthopristis chrysoptera, Linnaeus,
family Haemulidae), can dominate reef fish communities in terms of biomass
and are considered of great ecological and commercial importance (Gaut
and Munro, 1983). The groupers (represented by the black sea bass, Centropristis
striata, Linnaeus, family Serranidae), are large territorial piscivores
and are considered apex predators within the reef fish community.
Experimental System
The facility in which these studies were conducted was constructed
from the ground up with funds provided by National Sea Grant through
the Office of Applied Research. The system was designed to integrate
with the existing mariculture experimental system at CCFHR and consisted
of two buildings, the greenhouse that housed the experimental culture
tanks and the water conditioning building (Fig. 1).
Figure 1. Schematic diagram of greenhouse culture facility and
recirculating and conditioning system.
Water is conditioned in a recirculating system that includes
mechanical and biological filtration and temperature control. The
80 m² greenhouse (Van Wingerden Greenhouse Co.) was constructed on a
raised concrete pad poured to provide three floor gutters to allow the
outflow of re-circulated water to a return sump tank or to our system
outfall. Eight culture tanks constructed from concrete burial vaults
were set on the pad and supplied with re-circulated water and aeration. The
addition of this system to the CCFHR mariculture facility significantly
expanded capabilities to include the culture of plants under controlled
conditions.
Training
The training aspect of this project was accomplished through an agreement
with the Aquaculture Technology Program of Carteret Community College to provide internships
for undergraduate students and by the participation of an Oak Ridge Institute for Science and Education (ORISE) fellow, James Morris. In
addition, students from the University of North Carolina at Wilmington and Smith College participated as interns. Students received hands on
training in various aspects of aquaculture while providing critical labor
towards accomplishing the goals of the project. James Morris received
extensive training in the development of hatchery stocks, systems and
experimental design. He continues to work at the Laboratory where
he is now responsible for operation of the seawater system and studies
the invasive Lionfish (Pterois volitans) and red porgy (Pagrus
pagrus). The greenhouse facility has and continues to provide
various teaching opportunities with local universities and colleges including
class tours and demonstrations for students from Elizabeth City State University, East Carolina University, and Carteret Community College Aquaculture Technology
program.
Project Results and Discussion
Comparative studies with these behaviorally distinct species demonstrate
that polyculture produces fish that perform significantly better than
monoculture fish in behavioral challenge experiments designed to test
feeding (example Fig 2) and sheltering abilities. These results
are not surprising as the physical and biological complexity of polyculture
rearing systems would be expected to foster greater behavioral flexibility
and better performance in challenge experiments.
Figure 2. Mean times in seconds (+SE) required
to locate food in the dark by black sea bass cultured at four densities
in monoculture and in polyculture with oysters.
Improvements in behavioral quality were not made at the expense of
overall production. Survival of both species was similar in monoculture
and polyculture systems. Growth of black seabass juveniles was
similar in polyculture and monoculture, while, pigfish grew faster in
polyculture than in monoculture (Fig 3).
Figure 3. Length weight relationship of pigfish (Orthopristis
chrysoptera) cultured in four paired monoculture and polyculture
rearing tanks.
A consistent difference in experiments for both fish stocks was production
of a greater size range in polyculture than in monoculture systems. Greater
size variability appears to reflect the expression of a greater range
of behavioral phenotypes and can be viewed as a fundamental advantage
in the culture of fish for release to the wild. Cohorts in the wild retain
a wide range of size, presumably in response to temporal and spatial
variability in natural conditions and in behavior. High spatial and temporal
variability in the wild may allow survival of both shy (slow growing)
and bold fish (fast growing). Some habitats and time periods may
provide a selective advantage for aggressive fish while under different
conditions shy fish survive better. Polyculture appears to allow
expression of both shy and bold phenotypes while monoculture favors expression
of aggressive behavior.
Behavioral superiority of polyculture fish appears to be rooted in
differences in sensory abilities of fishes. Behavioral trials suggest
that polyculture fish had more acute olfaction and better vision in low
light conditions than monoculture fish. Direct evidence for differences
in neural development between fish groups, such as difference in brain
size or the extent of neural connection, have not been investigated and
will be a priority in future studies. Future work should also investigate
differences in the environment that the two systems provide. Preliminary
investigations of oxygen dynamics in the two systems suggest significant
differences between them in water quality (Fig. 4). Oxygen differences
must be related to the inclusion of plants in polyculture systems and
are likely to be reflected in other water quality parameters and ultimately
important to fish health. An outbreak of a parasitic dinoflagellate
in our grunt experiment provided evidence that grunts reared in polyculture
had higher resistance than monoculture fish and we suspect that this
was due in part to differences in water quality between the systems. The
costs in labor and material for the two systems should also be considered. Our
experience suggests that although materials and set up labor are greater
for polyculture systems.
Figure 4. Dissolved oxygen as percent saturation from two
sets of paired tanks monitored for four day periods with a hydro lab
water quality meter.
routine maintenance costs are greater for monoculture as it requires
time consuming daily cleaning. Production of habitat forming species,
such as oysters from the black seabass polyculture system could improve
the economics of polyculture systems.
In summary, comparative studies detailed in this report provide evidence
that polyculture represents a promising technique relative to conventional
monoculture for the production of fish behaviorally suitable for stocking. This
report supports future development of polyculture systems and more detailed
investigation of their impact on physiological development and health
of cultured fish, the physical dynamics of the culture environment and
the economics of aquaculture.