Now materials, floor, backdrop, lights, camera.

import bpy

def newmat(name):
    m=bpy.data.materials.new(name); m.use_nodes=True
    return m, m.node_tree.nodes["Principled BSDF"], m.node_tree

# ---- BODY: goldfish orange with scale pattern (procedural) ----
mb,bsdf,nt=newmat("GoldfishSkin")
out=nt.nodes["Material Output"]
tex=nt.nodes.new("ShaderNodeTexCoord")
mapping=nt.nodes.new("ShaderNodeMapping"); mapping.inputs['Scale'].default_value=(6.0,3.0,4.0)
wave=nt.nodes.new("ShaderNodeTexWave"); wave.inputs['Scale'].default_value=1.0
wave.inputs['Distortion'].default_value=2.5; wave.wave_profile='SIN'; wave.bands_direction='Z'
noise=nt.nodes.new("ShaderNodeTexNoise"); noise.inputs['Scale'].default_value=8.0; noise.inputs['Detail'].default_value=6.0
ramp=nt.nodes.new("ShaderNodeValToRGB")
ramp.color_ramp.elements[0].color=(0.85,0.18,0.02,1)
ramp.color_ramp.elements[1].color=(1.0,0.55,0.08,1)
mixs=nt.nodes.new("ShaderNodeMixRGB"); mixs.blend_type='MULTIPLY'; mixs.inputs['Fac'].default_value=0.35
# gradient belly->back lighter
grad=nt.nodes.new("ShaderNodeTexGradient")
sep=nt.nodes.new("ShaderNodeSeparateXYZ")
gmap=nt.nodes.new("ShaderNodeMapping"); gmap.inputs['Location'].default_value=(0,-0.5,0); gmap.inputs['Scale'].default_value=(0,0.45,0)

nt.links.new(tex.outputs['Object'], mapping.inputs['Vector'])
nt.links.new(mapping.outputs['Vector'], wave.inputs['Vector'])
nt.links.new(tex.outputs['Object'], sep.inputs['Vector'])
nt.links.new(sep.outputs['Z'], gmap.inputs['Vector']) if False else None
nt.links.new(tex.outputs['Object'], gmap.inputs['Vector'])
nt.links.new(gmap.outputs['Vector'], grad.inputs['Vector'])
nt.links.new(wave.outputs['Fac'], mixs.inputs['Color1'])
nt.links.new(grad.outputs['Fac'], ramp.inputs['Fac'])
nt.links.new(ramp.outputs['Color'], mixs.inputs['Color2'])
nt.links.new(mixs.outputs['Color'], bsdf.inputs['Base Color'])
bsdf.inputs['Roughness'].default_value=0.28
bsdf.inputs['Subsurface Weight' if 'Subsurface Weight' in [i.name for i in bsdf.inputs] else 'Subsurface'].default_value=0.15

# ---- FINS: translucent orange ----
def finmat(name):
    m,bs,nt=newmat(name)
    bs.inputs['Base Color'].default_value=(1.0,0.42,0.10,1)
    bs.inputs['Transmission Weight'].default_value=0.7
    bs.inputs['IOR'].default_value=1.1
    bs.inputs['Roughness'].default_value=0.25
    bs.inputs['Alpha'].default_value=0.9
    return m
finm=finmat("FinMat")
tail.data.materials.append(finm); dorsal.data.materials.append(finm)
for p in ("PectoralFin.L","PectoralFin.R"):
    bpy.data.objects[p].data.materials.append(finm)

# ---- EYES ----
eye=bpy.data.materials.new("Eye"); eye.use_nodes=True
eb=eye.node_tree.nodes["Principled BSDF"]
eb.inputs['Base Color'].default_value=(0.01,0.008,0.006,1)
eb.inputs['Roughness'].default_value=0.05
eye.node_tree.nodes["Principled BSDF"].inputs['Coat Weight'].default_value=1.0
for n in ("Eye.L","Eye.R"):
    bpy.data.objects[n].data.materials.append(eye)

# ---- FLOOR: big disc (a circle any child names) ----
bpy.ops.mesh.primitive_cylinder_add(radius=14, depth=0.2, location=(0,1.5,-1.65))
floor=bpy.context.active_object; floor.name="FloorDisc"
fm=floor.modifiers.new("bev","BEVEL"); fm.width=0.06; fm.segments=4
floor.data.materials.append(bpy.data.materials.new("Floor"))
fl=floor.data.materials[0]; fl.use_nodes=True
fb=fl.node_tree.nodes["Principled BSDF"]
fb.inputs['Base Color'].default_value=(0.16,0.30,0.34,1)
fb.inputs['Roughness'].default_value=0.35

# ---- WATER BACKDROP: world volume-ish via background + big sphere shell ----
w=bpy.data.materials.new("Water"); w.use_nodes=True
wn=w.node_tree
wn.nodes.clear()
em=wn.nodes.new("ShaderNodeEmission"); em.inputs['Color'].default_value=(0.05,0.28,0.36,1)
em.inputs['Strength'].default_value=1.0
bg=wn.nodes.new("ShaderNodeBackground"); bg.inputs['Strength'].default_value=1.0
bg.inputs['Color'].default_value=(0.05,0.28,0.36,1)
outn=wn.nodes.new("ShaderNodeOutputWorld")
wn.links.new(bg.outputs['Background'], outn.inputs['Surface'])
bpy.context.scene.world=w

# light shafts / god rays hint via volumetric in world? keep simple: add subtle volume to world
vol=wn.nodes.new("ShaderNodeVolumeScatter")
vol.inputs['Color'].default_value=(0.4,0.75,0.8,1)
vol.inputs['Density'].default_value=0.010
wn.links.new(vol.outputs['Volume'], outn.inputs['Volume'])

result={"ok":True}


Traceback (most recent call last):
  File "<repo>\.runner\blender-mcp-v1.0.0\addon\mcp_to_blender_server.py", line 230, in _execute_code
    exec(code, namespace)
    ~~~~^^^^^^^^^^^^^^^^^
  File "<string>", line 48, in <module>
NameError: name 'tail' is not defined