By Mor­gan Bender

With over 240 polar cod sam­pled, 30 weeks gone by, and 2.310 bags of pre­cise­ly pre­pared, weighed, chopped and labeled por­tions of calanus fish food, the long term chron­ic dietary expo­sure exper­i­ment has come a great dis­tance! Here is a small glimpse into what the sam­pling and exper­i­men­tal design has been like so far.

 Peri­od­ic mea­sure­ments on all fish in the exper­i­ment has allowed us to mon­i­tor growth through­out the repro­duc­tive devel­op­ment with­out remov­ing the fish from the exper­i­ment. It also gave us a chance to check up on our favorite indi­vid­ual fish progress over the span of many months.

 

This cold room at Kårvi­ka havbruk­stasjon out­side of Trom­sø has been the exper­i­men­tal grounds for the dura­tion of the project. The tem­per­a­ture of the water is now 3 degrees and the air isn’t much warmer, fol­low­ing the tem­per­a­ture vari­a­tions of Kongs­fjor­den on Sval­bard, where most of the fish are from.

Inside the cold room its polar night and has been since Novem­ber fol­low­ing a 79 degree North light regime. That means that work for us is also done in the dark. A total of ten tanks in this room are used for the dietary expo­sure exper­i­ments and are mon­i­tored con­tin­u­ous­ly by tech­ni­cians at the research station.

 Calanus cope­pods are one of the main food items for polar cod and we feed them a lot of it! The dif­fer­ent dos­es of crude oil are mixed with this bright orange zoo­plank­ton and fed to fish twice week­ly, the remain­ing food for the week is untaint­ed calanus. Feed­ing is done by tank and bio­mass of the tank is used to cal­cu­late how much food that tank receives. This amount is adjust­ed based on growth and sam­pling every 6 weeks.

 

 

 

 

 

 

 

 

 

 

Work has already been done in the lab look­ing at sex steroid hor­mones extract­ed from blood plas­ma. This will give us indi­ca­tions of hor­mone sig­nalling involved in repro­duc­tive devel­op­ment and pos­si­ble endocrine dis­rup­tion with chron­ic expo­sure to petro­le­um compounds.

 

 

Over the course of the exper­i­ment, small­er sam­pling points using unex­posed fish have allowed us to nar­row in on spe­cif­ic events in the repro­duc­tive process with regard to plan­ning full sam­pling events at crit­i­cal time points.

 

 

 

 

Sam­ples of gonads have under­gone his­to­log­i­cal analy­sis in pace with sam­pling to close­ly fol­low devel­op­ment. This meth­ods require deep con­cen­tra­tion as exem­pli­fied by Mas­ter stu­dent Libe Aranguren as she cuts 5 μm slices of tis­sue on a micro­tome using a very shape knife.

 

Our first results! His­to­log­i­cal analy­sis of female gonad sam­ples from ear­ly Decem­ber reveal that fish are near­ing spawn­ing. Yolk gob­ules are form­ing the cyto­plasm of the eggs as female fish invest more nutri­ents and ener­gy into the gonadal devel­op­ment. Tim­ing is most crit­i­cal for females thus we are fol­low­ing their devel­op­ment more closely.