Orian Tzadik

Graduation Year


Document Type




Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Marine Science

Major Professor

Christopher Stallings, Ph.D.

Committee Member

Ernst Peebles, Ph.D.

Committee Member

David Jones, Ph.D.

Committee Member

Steven Murawski, Ph.D.

Committee Member

Christopher Koenig, Ph.D.


Life history, nursery habitat, diet, stable isotopes, trace elements, fin-ray microchemistry


Diet and movements in fishes are often logistically challenging to study. Trace element and stable isotope analyses have advanced these fields considerably, but are still constrained by methodological impediments, such as the tendency towards lethal sampling. Studying endangered fishes is particularly challenging as representative samples are difficult to obtain. However, the information gained from such studies is often critical to the recovery of endangered fishes as knowledge of life history attributes has the potential to greatly influence the success of management strategies.

I tested the viability of using fin rays in fishes as a non-lethal approach to study diet and movement patterns over time. I then applied the methods I developed to study the life history of the critically endangered Goliath Grouper, Epinephelus itajara. Fin ray analyses have traditionally been used in age and growth studies, as well as in a limited number of projects that study the chemical constituents of the ray itself. Therefore, I first tested whether fin rays could be used as chronological recorders of chemical properties over time using a pseudo-experimental design. By using samples from various aquaria, I had documentation of the time of capture of every animal used. Based on the assumption that the otolith in fishes represents a conserved, chronological matrix, I compared trace element concentrations between the otolith and the fin ray of each individual. In addition I tested whether stable isotope values of δ13C and δ15N differed between the wild and captive life phases of each individual. Divalent ions and positively-charged transition metals (e.g., Fe, Co) in particular showed strong associations between the two structures, suggesting conservation of material. Stable isotope values of δ13C and δ15N differed between the wild and captive life phases in most of the fishes sampled, also suggestive of conserved matrices.

I then tested and modeled the differences in δ15N values over time between the populations of Goliath Groupers on the west and east coasts of Florida. In general, individuals on the west coast had lower overall values and a larger difference between juvenile and adult values. The mechanism that caused the differences between coastal populations may have been an artifact of the environment, rather than different feeding behaviors.

Last, I investigated different nursery habitats for Goliath Groupers in southwestern Florida. I characterized juvenile nurseries based on the chemical fingerprints of trace elements within the inorganic matrix of the fin rays. Groupings based on these fingerprints were surprisingly accurate and can be used to identify essential nursery habitat for the species in years to come.

This research demonstrated the efficacy of novel techniques that were used to gather information on the life history of a critically endangered fish in the state of Florida. The results can be used to influence management strategies in the future, particularly with regard to nursery habitat use.