1. Field Studies in Fish Feeding Deterrent Activities
of Selected Aldehydes:)
Amanda Moore, Chelcey Doss, and Bülent Terem
Chaminade University
Introduction
Materials and Methods
Results
Conclusion
References and Notes
1. Faulkner, D. J.; Ghiselin, M. T. Mar. Ecol.: Prog. Ser. 1983, 13, 295-301.
2. Ritson-Williams, R.; Paul, V. J. Mar. Ecol.: Prog. Ser. 2007, 340, 29-39.
3. Cimino, G.; Ghiselin, M. T. Chemoecology. 1999, 9, 187-207.
4. Scheuer, P. J.; Terem, B. Tetrahedron. 1986, 42, 4409-4412.
5. Scheuer, P. J.; Schulte, G. R. Tetrahedron. 1982, 38, 1857-1863.
6. Wainwright, P. C.; Bellwood, D. R. In Coral Reef Fishes: Dynamics and Diversity in a Complex
Ecosystem; Sale, P. F., Ed.; Academic Press: San Diego, 2002, 33-55.
7. Average pellet weights
8. Values estimated
Nudibranchs are soft-bodied mollusks which lack any means of physical defense
such as a shell, and thus rely on secondary metabolites as defense chemicals to deter
predators.1
Over the last few decades many compounds isolated from nudibranchs were
reported in literature as defense chemicals due to their feeding-deterrent properties
against fish, although experiments carried out to determine such activity are often
varied, in terms of methods utilized, and not always reproducible.2,3
We report here the preliminary results of a field-assay we have designed based on
previous work carried out with ichtyodeterrent constituents of the nudibranchs
Chromodoris youngbleuthi (Glossodoris rufomarginata) and Chromodoris
albopustulosa (Goniobranchs albopustulosus).4,5
Our long-term objective is to characterize minimum structural features of related
compounds which display such activity. We also believe that it might be possible to
utilize the field-assay in activity-guided separation schemes.
It has been postulated that the 1,2-dialdehyde functionality of the sesterterpene and
the sesquiterpene metabolites is responsible for the fish-deterrent activity. The
stereochemistry of the dialdehyde moiety is an additional contributing factor to the
extent of activity observed.4,5
We tested the following commercially available aldehydes at different doses as
model compounds, as well as an extract of C. youngbleuthi.
Acknowledgements
• This project was supported by grants from the National Center for Research Resources
(5P20RR016467-11) and the National Institute of General Medical Sciences (8 P20 GM 103466-11)
from the National Institute of Health. The content is solely the responsibility of the authors and do not
necessarily represent the official views of the National Institute of Health
• We would like to thank Dr. Henry Trapido-Rosenthal for helpful discussions, Ms. Brandi Sasaki for her
help in setting up aquaria, and Mr. Gary Triggs for his assistance in diving.
Future Studies
• Field-assays will be repeated to ensure reproducibility and statistical significance.
• Further commercially available dialdehydes will be used as model compounds.
• Further experiments in dose v.s. deterrent activity relationships will be carried out
for each model compound in an attempt to determine ED50 (Effective Dose)
values.
• Derivatives of 2-cyclohexene-1,2-dicarboxaldehyde (4) will be synthesized and
their fish feeding deterrent activities will be determined in field-assays.
Model compounds were incorporated into commercially available “sinking” fish
pellets (Aqueon Bottom Feeder Tablets: weight range 210 mg to 290 mg; diameter
12 mm): dichloromethane (DCM) solutions of model compounds at various
concentrations were added to the pellets drop wise making sure not to saturate the
pellets. Pellets were left on the bench-top for a period not less than one hour until the
dichloromethane evaporated completely.
Materials and Methods Continued…
Since the work reported here is a preliminary investigation and focused on method
development, a full statistical analysis of the results was not carried out.
• The potentially complex field-assay was purposefully designed to have simple
parameters so that each test could be completed in a short time while maximizing
the number of fish involved.
• Pellets treated with higher doses of model compounds resulted in higher numbers
of rejections.
• Pellets treated with benzene-1,2-dicarboxaldehyde (o-phthalaldehyde), (3), even
at lower doses, resulted in higher number of rejections compared to mono
aldehyde model compounds.
• In view of the rapid approach of fish to the pellets offered, followed immediately
by a bite, it is unlikely that olfactory cues played any part in fish-deterrent
activity.
Model Compounds
0
10
20
30
40
50
60
70
80
90
100
Rejections(%)
Aldehydes Tested
Field Assay: Percent Rejection of Test Samples
Compound 1 Compound 2 Compound 3 Nudibranch Extract
n=20
n=20
n=20
n=6
n=18
n=19
n=5
Chromodoris youngbleuthi
(Glossodoris rufomarginata)
Chromodoris albopustulosa
(Goniobranchus albopustulosus)
Model
Compounds
Pellet
Weights
(mg)7
Weight of
DCM per Pellet
(mg)
Weight of
Model Samples
per Pellet (mg)
Number
of Pellets
Made
Rejections /
# of Pellets
Used
Percent
Rejected
1 250 250 10 20 0/20 0.0%
1 250 125 125 20 13/20 65.0%
2 250 250 10 20 1/20 5.0%
2 250 125 125 6 5/6 83.3%
3 250 5008 20 18 11/18 61.1%
3 250 5008 40 19 17/19 89.5%
Nudibranch
Extract
250 650 60 5 5/5 100.0%
Feeding Experiments: Feeding assays were conducted using SCUBA at a location
popularly known as “Waikiki Turtle Canyon” (GPS: N 21° 16' 25.0", W 157° 50'
21.7") at a depth of -10 m.. The site was selected due to the presence of dense
populations of reef fish. Pellets treated with model compounds were placed in zip-
lock bags (3-4 pellets per bag) to keep them dry until a school of fish (15 or more
individual fish) was within the immediate vicinity of the diver. Pellets, one at a time,
were offered to the fish and the feeding behavior of the following species was
monitored closely: Melichthys niger (Hawaiian Black Trigger or humuhumu 'ele
'ele). It took less than a minute for the fish to capture the pellet offered. Suction
feeding, which is believed to be the main method of prey capture with trigger fish,6
was observed during the dives. “Unpalatable” pellets were quickly rejected by the
fish by spitting out the whole pellet. A pellet was considered rejected even when it
was pursued by other fish after it was expelled, as long as the original fish did not
attempt to bite it for a second time.
Data