Your friend is an amateur aquarist learning to breed clownfish. She had one successful clutch of eggs, and moved the mother and fry with their anemone to a separate tank leaving only male fish behind. Now, she is surprised to find that a new female fish has appeared in the original tank. What is the most likely explanation for this?

Question

A.  Some anemone species secrete pheromones that control the sex of fish as a way to regulate predation. Removal of the anemone allowed a new female to develop.
B.  In urban areas, tap water is polluted with contamination from endocrine disruptors such as BPA and PCBs. When she removed some of the tank water for the new tank, she should have replaced it with bottled water.
C.  Clownfish are protandrous hermaphrodites that respond to social cues. Removal of the dominant female allowed the second-largest fish to transform into a female.
D.  Clownfish synchronize their mating based on seasonal cues indicated by salinity. When she replaced some of the tank water, the lower salinity caused the fish to change into a female.

Clarify Question
What is the key concept addressed by the question?

What type of thinking is required?

Gather Content
What do you already know about the reproductive modes of fish? What other information is related to the question?

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?


Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  Clownfish are protandrous hermaphrodites that respond to social cues. Removal of the dominant female allowed the second-largest fish to transform into a female.

Clarify Question
What is the key concept addressed by the question?
     · The concept of gender in fish is addressed in this question.

What type of thinking is required?
     · Evaluate level:
       o This question is asking you to weigh and judge, or evaluate, the presence of a female fish from a previously male individual.


Gather Content
What do you already know about the reproductive modes of fish? What other information is related to the question?
     · A dominant female fish can prevent the development of other fish in the same area.
     · If the dominant female fish is removed, another fish can develop into a reproductive female.
     · Sequential hermaphroditism occurs when an individual is one gender at one point in life, and then can reproduce as another gender at a later point in life.
     · Protandry is a form of  sequential hermaphroditism in which an individual reproduces as a male first, then reproduces as a female later.


Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
     · The events in this example can only be explained by protoandry. An individual was initially male, but was later able to reproduce as a female.
     · Clownfish are protandrous hermaphrodites. This is the only known mechanism that allows a mature adult male to change into a female.


Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
     · Evaluate level:
       o Answering this question correctly depended on your ability to weigh and judge, or evaluate, sex determination in fish. If you got an incorrect answer, did you remember that fish can be sequential hermaphrodites, or the that this change can be initiated by the removal of a female fish from a group? Did you have trouble weighing the merits of reproductive modes with environmental cues to determine the correct answer?