Friday, March 15, 2013

The Opakapaka Pens

There is a theme I have noticed whenever we introduce the opakapaka pens during the HIMB tours, and that is the utterance of "yum."  It isn't always "yum."  Sometimes it's, "Honey, I told you we should have reserved the beach house for lunch."  No matter how it's phrased, the recurring sentiment expressed by many visitors is a fondness for the flavor of these fish.  Fortunately for consumers, chefs, and the species, the opakapaka at HIMB are serving a much greater purpose than being food.

Drawing by Leon Weaver
The Deep 7
Opakapaka, also known as pink snapper, ruby snapper, and Pristipomoides filamentosus, are members of a compilation of benthic fishes known as the Deep 7.  This septet comprises more than 60% of the bottom fish fishery[1].  In 2005 the bottom fish fishery of the Main Hawaiian Islands (MHI) was identified as being over fished by the Secretary of Commerce. Two years later, due to excessive fishing pressure, the bottom fishery was officially closed for the first time.  That same year the bottom fish fishery reopened throughout the Hawaiian Island Chain with new restrictions and a newly impossed closed season[2].  In 2011, the bottom fishery in the North Western Hawaiian Islands (NWHI) became closed though the Hawaii Bottomfish Fishery website still says it is OK to eat Deep 7 fish caught in the NWHI . . . although this makes limited sense.

deep 7 bottomfish
a) `ula`ula koa`e or onaga (Etelis coruscans); b) `ula`ula or ehu (Etelis carbunculus); c) kalekale (Pristipomoides sieboldii); d) `opakapaka (Pristipomoides filamentosus); e) `ukikiki or gindai (Pristipomoides zonatus); f) hapu`u (Epinephelus quernus); and g) lehi (Aphareus rutilans)
Into Action
In an effort to aid the declining wild population, Dr. Clyde S. Tamaru led a group of researchers and students seeking a way to produce juvenile opakapaka in captivity.  The bottomfish research at HIMB had three main goals: to assess the restricted fishing zones using tagged juveniles, to determine if a sufficient number of offspring raised in and released from captivity could enhance the wild population, and to determine the feasability of producing juvenile opakapaka on a commersial scale[4].

In 1999, juvenile opakapaka were caught from the wild and kept in the floating net cages at HIMB.  The group must have done something right, because in 2001 the brood stock began spawning naturally, and have continued to do so ever since. 

It would seem to me that the hard part was over with and it would be smooth sailing from there, right?  I would be wrong.  Any parent knows that keeping a child well nourished requires an exorbitant amount of time and energy. The minuscule opakapaka offspring were no different.  Just finding the right "baby formula" of copepod nauplii required extensive experimentation.  As larval opakapaka grew, their tastes changed and they needed new foods, which also had to be determined by experimentation.

Pictomicrograph of a two week post-hatched ‘ōpakapaka larvae [4].
Photo by Clyde Tamaru
Despite the challenges, the researchers were successfully able to grow the offspring up to the size their parents had been when they were collected in 1999.  The juveniles were tagged and released in the same location their parents had been collected from. 

The HIMB Education Department, headed by Dr. Malia Rivera, continues to monitor the spawning behavior of the opakapaka.  Documenting what time of the year spawning begins and ends is essential for determining seasonal fishery closures to prevent the cropping of spawning adults.  The spawning period of opakapaka is also of interest to Dr. Rivera and the Education Department because it is utilized in a laboratory exercise that introduces high school students to marine fish aquaculture. 
The material covered in the hatchery lab is very interesting and directly applicable.

Did you know that opakapaka eggs are infused with a touch of fresh (less salty) water just before spawning?  Fresh water is less dense than the salt heavy sea water, so the buoyant eggs float to the surface.  Participating students are able to collect the eggs from the surface of the water for analysis in the lab.  By manipulating the salinity and density of the egg-containing water sample, students can affect the buoyancy of the eggs, allowing easy removal of excess debris within the sample.  Afterwards the eggs can be quantified and examined for percent fertilization.  The eggs take only 31 hours to hatch after being fertilized.  By identifying the embryonic stage of development, it is possible to estimate when the eggs will hatch.  Upon completing this exercise, students are able to quantify approximately how many eggs will hatch, when hatching will occur, and how much food is necessary to sustain the larvae; just like a professional hatchery.

Looking Forward
With the closure of the NWHI bottomfish fishery, fishing pressure has increased in the Main Hawaiian Islands. Due to consumer demand for the delectable opakapaka, there is serious economic pressure to increase yield.  While increasing the scope of marine protected areas and placing additional restrictions on bag-limits and open seasons would aid in wild stock recovery, overly zealous protective measures would be detrimental to the fishing industry and consumers.  Using aquaculture to enhance wild stocks or to directly produce fish for market seems like a reasonable solution for fish, industry, and consumers alike.  With luck, the bottomfish researchers at HIMB will develop a method in which they can repetitively raise juvenile opakapaka in captivity.


Kupu/Americorps Intern
Community Education Program

For more information on the bottomfish research and the content of the Marine Fish Aquaculture Lab, follow the "Introduction to Marine Fish Aquaculture: Spawning and Larval Development of Opakapaka" link listed below.

1. The Center for Tropical and Subtropical Aquaculture: "Update on the Hatchery Production of the Opakapaka, Pritipomoides filamentosus"

2. Hawaiian Bottomfish Fishery

3. Hawaii Department of Aquatic Resources (DAR):

4. Hawaii Institute of Marine Biology Education Program "Introduction to Marine Fish Aquaculture: Spawning and Larval Development of Opakapaka"

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