Marine-Fish.md

+The Marien fish section includes fish caught from the sea. Marine fish are essentially a 'free' resource in the model. The model can decide how much fish to take provide it is less then the marine fish constraint.   
+
+```mermaid
+graph TD;
+  MarineFishAV["Marine Fish Constraint"]-->MarineFish["Marine Fish"];
+  MarineFish["Marine Fish"]-->ProcTrans["Processing & Transport"];
+```
+
+# Data
+
+The marine fish section includes the following csv file.
+
+* Capture_Fish
+  * Marine fish caught per year in tonnes. 
+
+# Equations
+
+The marine fish section only includes one equation described below.
+
+## Marine Fish Constraint (1) 
+
+```
+EQUATION eCaptureFishAv(Country,Region,FishSpecies) "Constraint, marine fish is equal or less then marine fish available per country, region and fish species in Mg per year";
+         eCaptureFishAv(CR,FishSpecies)$MarineFish(CR,FishSpecies)..
+         vMarineFishMg(CR,FishSpecies) =L=  MarineFish(CR,FishSpecies) * ScenarioControlsModel('Util.MFish')
+;
+```
+Marine fish must be equal or less than marine fish constraint. This allows the model to select how much fish it would like to use. The **ScenarioControlsModel('Util.MFish')** can be set in Scenario_Controls.csv.
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