Biosampling Basics

Purpose: Collecting large quantities of fish can have an undeniable effect on the populations strength and stability. This makes it vital for fishery management to have an accurate understanding of each species’ growth and maturity. Currently, relatively little is known about the growth and maturity of commonly caught coral reef species within Hawaiian waters. This is where biologists, such as us at Poseidon Fisheries Research, come into play. We are responsible for the collection, analysis and reporting of the life history traits that are specific to these species. Examples of life-history information would be investments an individual makes in growth and reproduction, the time at which they mature along with maximum age and sizes. Currently, there are little life history data available for many Hawaiian populations of many commercially and recreationally caught reef fish. The ongoing purpose of this study is to collect missing life-history information for Hawaiian populations of 9 species of reef fish. In doing so, we hope to obtain a better understanding of each species.

The Process: In order to conduct this study, we initially conduct a routine check of local fish vendors to get a monthly estimate on all the different reef species being caught and sold here in Hawai’i. However, we only do in-depth life history studies on around 9 species. In order to do this, we first start by measuring the weight and length of each fish. Afterwards, we dissect the fish in order to extract their reproductive organs and otoliths. 

    The process begins with the star of our study, the fish! We begin with the collection of fish from markets, fisherman or even try to catch them ourselves (often without luck). We can then transport the fish back to our lab where we have all the equipment necessary to dissect them and collect and store samples.


      Dissections: Dissecting fish can be tedious and messy at times. This is why we employ specific methods of dissection depending on the morphology of that species. For example, the gonads in a surgeonfish are located below the stomach and digestive organs, while in a table boss the gonads are positioned above the stomach. In order to make the dissection easier, we will cut these fish differently. 
      We use two different methods for extracting otoliths, including the “scalp” method which is executed by removing a section of the head just above the eye. This process removes the top of the brain casing and gives us access to the brain. We can then remove the the brain and pull out the otoliths which will be sitting in two small pockets beneath it. The second method involves removing the otoliths ventrally and entering the brain case from underneath. Both methods take a degree of practice and patience.
      In surgeonfish the gonads are removed by making a shallow vertical cut through the tissue, extending from the top of the head, down towards the anal fins. The spine is then cut and the head of the fish is pulled down and away from the body. If done right, the internal organs will separate from the body of the fish and all that will be left inside are the gonads.
     In the typical reef fish, the gonads are located above the gut. Therefore we can begin by making a ventral cut through the fishes’ belly. This is a commonly used practice when gutting fish. Then continue to pull out all of the internal organs, and the gonads will be sitting on top of the gas bladder.

       Aging: The otoliths are inner ear bones located beneath the brain that help the fish balance and orientate itself in the water. Each year, as the fish grows, their ear bones grow as well, depositing an annual layer of material. These deposits are the key to determining the age of the fish. By taking a thin cross section of an otolith and viewing it under a microscope (pictured left), you are able to see dark bands present on the bone, each band marking one year. Similar to reading rings on a tree!                                             Determining Maturity: The reproductive organs, called gonads, are used in determining the sexual maturity of the individual. First, gonads are removed in a method appropriate for that species. Depending on the physiology of the species, gonads can be   

located in different positions inside the body cavity. This determines how we cut the fish in order to have easy access to the gonads. After the gonads are removed and weighed, a section is cut from them and placed into a small plastic cassette. The samples are then processed by slicing them into very thin sections and fixing them to a microscope slide (pictured right). Maturity of each slide is then carefully analyzed to determine sex, maturity and stage of reproduction..

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