Things we do for class - Species pages

For most of the last semester, we have been working on these species pages for our taxonomy class. Eunice's page is none other than being focused on what she does best, ANTs. And so her target species is Proatta butteli, a really interesting ant. As for me, I have decided to focus on a bird species, the Common Hill Myna (Gracula religiosa). The reason for doing so is because I have a love for birds too (not just dung beetles) and this species is one of my favourites.

Screenshots of our species pages. TOP: Proatta butteli. BOTTOM: Gracula religiosa

Our pages are found at this website, http://taxo4254.wikispaces.com/, together with other species pages done by other students as well. Enjoy~

Cartography and Visualisation IV: Map Design

Visual Variables

Visual variables can vary in the following manner:

Size: the thickness/size of a symbol

Value: the lightness/darkness of a colour
Hue: shade of a colour (element on the colour wheel; a pure colour)
Saturation: purity of the colour; also known as chroma
Orientation: the direction of the symbol
Shape: the type shape used for symbolisation
Arrangement: the way in which the symbol is arranged
Texture

Colours 

Colours used limited by: 1) human vision, 2) colour specification of systems, 3) colours in map design

1) Human Vision

A beautiful video on the physics of colour

Electromagnetic spectrum: 400nm-700nm for the visible range

Two Theories on vision: 

Trichromatic theory: condition of possessing independent channels for conveying colour information, derived from three different cone types (cone cells). In reality there might be more than 3. (by Thomas Young, 18^th century)

Opponent-process theory: psychological model that accounts for wide range of behaviours, including colours. We perceive colours as three independent receptor types of opposing pairs: white v. black, blue v. yellow, red v. green. (by Ewald Hering in the late 17^th century)

A lecture on the Colour-Opponent Theory

It has been shown that both work hand-in-hand (physiological v. psychological).

Simultaneous contrast: appearance of a colour in a display depends on colour that surrounds it

Successive contrast: colours modified in the order they are seen 

A video illustrating simultaneous colour

2) Colour specification of systems

Things to note:
Printer-friendly
Colour-blind friendly
Black/white printer

3) Colours in map design

Colour conventions: e.g., blue for water, green for lush/thick vegetation, brown for land surfaces, red with warm/blue with cool temperature; red to advance, blue to retreat (because our eye lens bulge when we see red, similar to seeing objects close up)

Using it for figure-ground contrast

Schemes possible (i.e., http://colorbrewer2.org/)

• Qualitative schemes: represented by the difference in hues
• Binary schemes: represent with differences in value, holding hue constant, unless it is used to represent qualitative difference (then hue difference might be fine)
• Sequential schemes: represent data in sequence; generally represented with value difference, hue held constant
• Diverging schemes: focus on a mid-point and variations out from that mid-point

Colour Brewer. Allows you to select for sequential, diverging colour schemes. Not included: binary scheme.

Typography

Why text are required in a GRAPHIC map:

• Labelling: clear and unambiguous communication; ‘symbols for meaning’
• Organising: structure, visual hierarchy, location, spatial extent
• Explaining: graphics cannot explain everything, title/legends/explanatory text

Typography is the usage of design in text (type).

Letter form components:

X-height: height between base and mean-line; a font with a large x-height is said to be more readable (though a quick search on the internet says that this is a myth)

Serif: the line at the end of a letter

Type characteristics:

Type family: a group of type designs that reflect common characteristics

Typeface: combination of type of a particular style and family

Style: italics used more for natural features; also for identification of publication though it is harder to read, water features;

Font: a set of all alphanumeric and special characters of a particular type family, style and size

Spacing: (between letters) kerning, (between lines) leading; letter spacing for words in uppercase so it is more readable (i.e., outline is more visually dominant than inner space)

Type size: implies ordered relationships; larger of greater importance; small sizes should be avoided (4-5point)

Type weight: bold implies greater quantity; light type may not always be available in a mapping type

Case: lower case for easier word recognition, uppercase for mountain ranges, lower cases for other natural features; more important/ larger features with the usage of uppercase

Type face and lettering harmony: one typeface should be used across the map; multiple variants of a type face can be used

Masking: background (“highlight”)

Hallow: border around text

Callout: with speech bubble

Type is important to convey the message you wish to give to your audience.
As much as possible, it should be light in shading, enough kerning between the letters.
Capitalisation should be avoided unless its for a major area.
Finally, the most important thing is readability. :)

History of Typography

 

What is typography

Layout

*this section is still work in progress

Planar Organisation

Balance

Rudolf Arnheim’s visual principles of balance: weight & direction

Variables that confer more/less weight
Location: at structural net (via golden ratio)/ not at structural net, right/left, top/bottom, away from centre/near centre
Shape: regular/irregular, compact/not compact
Colour/ Interest/ isolation: type of colour (red/blue, bright/dark, white/black), instrinsic interest/none, isolated/surrounded
Size: large/small

Variables that confer direction or not
Location: isolated/ 'is surrounded'/ 'is in centre'
Shape: can direct with axes
Subject matter: can direct based on interest

Internal organisation

WHAT: An ordered map arranges the graphic and/or intellectual elements into a composition that develops a clear visual expression
HOW: Through alignment in two steps: 1) Intraparallelism - aligning map elements with each other to simplify the map 2) Alignment corrections via continual separations between groups of elements
WHY: Reduces tension

source: http://www.gitta.info/LayoutDesign/en/html/DefOrgMapEle_learningObject3.html

Hierarchical organisation

Figure: important objects that should stand out against the background

Ground: less important objects that form the background

Perceptual grouping: the map viewer spontaneously combines elements in the visual field that share similar properties, resulting in new forms or ‘wholes’ in the visual experience; this can be done so by shape, size or proximity

Contrast: visual differences between the map features that allow us to distinguish one from another, achieved through considering line/ texture/ colour (value and hue)

-> Line contrast: edges

-> Texture contrast: pattern of small symbols repeated in such a way that the eye can perceive individual elements

-> Value contrast: e.g., using a dark colour as the background and lighter colour as the foreground (Arnheim’s rule)

Closure: the tendency for perceiver of the map to complete unfinished objects

Vignetting: graphic emerging from an edge or border resulting in a continuous gradient of brightness (for land-water contrast)

Cartography and Visualisation III: Map Elements

This is gonna be a short post. It'll cover the essential elements of a map - what most maps should have within the "area". However, it is subject to the requirements of the publication/ report.

This is Part III of the four-part instalment on: 

1) projections,
2) geographical phenomenon and data representation,
3) map elements,
4) map design (colour, typography, planar organisation and hierarchical organisation)

Just a teaser to begin with: WHY MAPS ARE COOL

Ok back to business:

Map was made by myself for an assignment.

Title/Subtitle: for a concise description of the map’s theme (not wordy, no abbreviations). This can be replaced with a caption, if in the case of a report.

Legend: defines all of the thematic symbols of a map; symbols that are self-explanatory or not directly related to map’s theme are normally omitted

Frame line: encloses the entire map and neat line: encloses the mapped area

Data source, credits: where the data for the thematic map is obtained, base information normally omitted

Scale: representative fraction of the map to reality and could be a verbal or bar scale. However, whether to use a scale might depend on whether the map is equal-area or not. If it is not equal area, then putting the scale bar is meaningless.

Orientation represented by north arrow, graticule. However, whether to use a north arrow might depend on whether the angles varies throughout the map. If it does significantly, then adding the north arrow is pointless.

Inset: a smaller map included within the context of a larger map

Place names/ labelling

Cartography and Visualisation II: Geographic Phenomenon & Data Representation

In this second instalment, I will cover Geographic Phenomenon & Data Representation.

This is Part II of the four-part instalment on:

1) projections,
2) geographical phenomenon and data representation,
3) map elements,
4) map design (colour, typography, planar organisation and hierarchical organisation)

What is geographic phenomenon?

It is a data that is spatially distributed. It can hence be abrupt or smooth in nature (with reference to whether there is a break in the data, usually between enumeration units), and can also be continuous or discrete (with reference to the number of decimal places on the number).

Data can be qualitative (=deals with apparent qualities [subjective properties]), or quantitative (=type of information based on quantities [objective, measureable]).

Qualitative data -> nominal
Quantitative data -> ordinal (ranking), interval (arbitrary 0), ratio (non-arbitrary 0)

There are a total of FIVE common mapping methods.

How can geographic phenomenon be represented?

It is usually represented in a thematic map, which is made up of a basemap and a thematic layer. A thematic map usually shows a specific theme connected with a geographic area. This is as opposed to a general purpose map (=General purpose map: many types of information on one map; most atlas maps, wall maps, road maps fall into this category; the map aims to give a broad understanding of location and features of an area (e.g., location of urban places, type of landscape, major transportation routes).

Different types of data can be represented in different types of 'conventional methods'.

Choropleth: having enumeration units (e.g. area) bounded by isolines to represent a distinctive colour/shading to represent a particular geographical phenomenon; values represented can be derived or totals; areas represented are usually administrative areas or statistical areas

Choropleth map with different classification methods

Dasymetric: using ancillary information to map enumeration units at a finer scale; corrects for ‘ecological fallacy’ that occurs with choropleth mapping; uses standardized data but places areal symbols that take into consideration actual changing densities within the boundaries of the map

-> Enumeration units: (in the case of a choropleth map) a uniform unit representing a single data point and is bounded by lines

-> Classification methods: grouping data into various classes by a certain method (e.g., 1) equal interval; 2) standard deviation; 3) Quantiles; 4) Natural breaks (Jenks); 5) Arbitrary)

• Equal interval: each class occupies an equal interval along the number line
• Standard deviation: class boundaries are defined by standard deviation
• Quantiles: assures an equal number of values in each class
• Natural areas: idiographic data classification that classify data into distinct groups based on a histogram distribution; via visual inspection or Jenks optimization
• Arbitrary schemes: using arbitrarily-set classes; using regular rounded numbers having no relevance as distributional classes

Dot mapping: using dots to represent absolute numbers within an enumeration unit; the placement of dots can be uniform, geographically weighted (i.e., spatial autocorrelation) and geographically based (on ancillary information)

-> Ancillary information: complementary information that includes existing topographic maps, remote sensing data, meterological data, policies etc.

Isoarithmic: (e.g., isometric -> true point data to isoplethic -> conceptual point data) planimetric graphic representation of a three-dimensional volume via a system of line symbols to represent a 3D volume or mental construct; requires interpolation between control points

-> Interpolation: joining of points (i.e. control points) via a manual or automated process to form a continuous line representing a particular value

-> Manual interpolation: via methods of joining neighbouring control points with straight lines, to create lines of contours (isolines), in assuming that distribution of mapped changes in a linear fashion

-> Automated interpolation: via automated methods such as Delaunay triangles (via triangulation, triangle-based) Theissen polygons (via triangulation, polygon-based), Inverse-distance (gridding: making use of a grid and interpolating distances between nodes to get an estimation), Kriging 

Proportional symbol: a type of thematic map where data represented by a point symbol whose size varies with the data attribute values (goal of the map to show relative magnitudes [e.g., true point data or conceptual point data] of phenomena at specific locations); can be used for ordinal, interval and ratio data (quantitative data)

Proportional symbols, with range-grading (Dent).

Three Methods:

-> Absolute scaling: direct proportional scaling with the values it represents

-> Apparent-magnitude scaling: based on perception, with Flannery’s adjustment factor

-> Range-grading: (based on Dent 1999 or Meihoefer 1969) dividing data into groups, each group represented by a distinguishable proportional symbol; recommended to use five adjacent circles on a small scale map

Extra terminology:

Small scale map: large area

Large scale map: small area

Cartography and Visualisation I: Projections

I am writing a post about the terminologies in relation to Cartography and Visualisation, and in specific, how cartographic projections (i.e., the maps we hold in our hands) come about.

This is Part I of the four-part instalment on:

1) projections,
2) geographical phenomenon and data representation,
3) map elements,
4) map design (colour, typography, planar organisation and hierarchical organisation) 

The aim of this post is to be as concise as possible, adding definitions and diagrams to aid in your understanding of how projections came about, and also partly to help in my revision for the examinations (heh heh). The definitions are adapted in my own words from the online resources that I have read and my Cartography and Visualisation lecture notes.

Just a teaser to start:

Adapted from GE2227 notes. Redrawn by Eunice Soh.

Geoid: a hypothetical surface representing the form the earth’s oceans would take if there was no land and the water were free to respond to the earth’s gravitational and centrifugal forces; can vary up to 75 metres above/ 100 metres below the ellipsoid (i.e., orthometric height)

Here's a geoid viewer: http://geomatica.como.polimi.it/elab/geoid/geoidViewer.html

A video on geodesy

How all the cartography terminology are linked. First, one starts off with an ellipsoid which is a mathematical representation of the geoid. The ellipsoid is defined by its geodetic datum, with the following parameters: origin, semi-major axis and semi-minor axis. 

Reference spheroid/sphere/ellipsoid: a mathematically-defined surface that approximates the geoid, the truer figure of the earth, or other planetary body (e.g., WGS1984)

Datum:  a set of values that act as a base to which a geoid is referenced at a single point; (as geodetic datum): a model that describes the location, direction and scale relationships with respect to an origin on the Earth’s surface (i.e., semi-major axis [a], semi-minor axis [b], flattening ratio [b/a], origin); Singapore’s datum is SVY21 which is based on the WGS84 datum except for the difference in origin

A geographic coordinate system is a coordinate system that enables every location on the Earth to be specified by a set of numbers or letters.

Prime meridian: a longtitude which is defined as 0^o; it is arbitrary, unlike the equator (vertical)

Equator: a latitude which is defined as 0^o_, at the axis of rotation of the earth (horizontal)

What is a rhumbline (loxodrome)

Projected Coordinate Systems and their various properties. The black box are the actual names of the projection.

A projected coordinate system is a coordinate system projected from a geographic coordinate system, where a map projection is the systematic transformation of the curved, three dimensional surface of the planet into flat, two dimensional plane, resulting in distortion.

For a great video on projections, look here: http://education.nationalgeographic.com/education/media/selecting-map-projection/ and a cute cartoon about map projections: http://xkcd.com/977/

Another video on projections

How did the Mercator projection (azimuthal) come about 

Distortion: any projection that distorts the earth in some way (e.g., conformal -> angles preserved, areas distorted; equal area -> area preserved, angles distorted)

Certain projections can be a "compromise" (figure above).

A good read would be http://en.wikipedia.org/wiki/Map_projection

Decisions of a projection would depend on

• Properties of the projection
• Characters (scale, interrupted, aspect)
• Deformation across mapped area
• Projection centre
• Familiarity

Properties of a projection

Major factors

• Equivalence: Equal area 
• Conformality: Equal angles 

Minor factors

• Distance: Equidistance 
• Direction: e.g., Azimuthal

Things we do for class - Bivalve dissection

Chama pacifica Chamidae

Just last week we did another dissection practical. This time, for bivalves! We got to dissect a Meretrix sp. ("La La", a heterodont), Nuculana sp. (which was really tiny, a protobranch), Anodonata sp. ("Mussel", family Mytillidae, a pteriomorph), Anadara sp. ("Blood Cockle", a heterodont).

Bivalves are molluscs that are laterally compressed and have a hinge, enclosing two hinged parts. The shell is made up of calcium carbonate secreted by the mantle lobes and mantle. The calcium carbonate can be either aragonitic (nacreous inner layer - sheet or lenticular, prismatic, cross lamellar structure - simple or complex) or calcitic (outer foliose, prismatic). The calcium carbonate of a shell is never entirely calcitic though, mostly it is a mix of aragonite and calcite. Certain bivalves though, like oysters have almost all calcitic. On the contrary, some families are entirely aragonitic.

Lima vulgaris Limidae with wholly aragonitic shells

They have a D-larva split into two stages, Prodissoconch I and Prodissoconch II which have the velum to help it with motility with the exception of the Paleoheterodonts which have glochidium/ lasidium larvae.

They are generally split into different clades based on gill type, presence of palps, type of stomach, fusion of mantle & siphon position (higher taxa); hinge teeth type (higher or lower taxa); foot size, position of adductor muscles (lower taxa):

(photographs were identified by Tan Siong Kiat in 2011 as part of Project Semakau: bivalve page)

- Protobranch (small group, 3 orders, considered 'ancient', small in size, bipectinate lamellae (simple) gills with palp probocoides (for Nuculidae and Nuculanidae), foot frilled with papillae, do not filter feed but scrape detritus or symbiotic with sulphur oxidising bacteria in gills (only Solemyida))

e.g. Nuculana

- Paleoheterodont (mostly in the family Unionidae but there are 6 other families; mostly are freshwater except one of which is salt-water - Trigoniidae)

- Heterodont (unequal hinge teeth, eulamellibranch gills, mantle edges are fused at the posterior end as an inhalant tube) and Anomalodesmatans (typically lack hinge teeth, aragonitic shells, long siphons, fourth pallial aperture, vestigial gill filaments; Septibranchia is carnivorous with a type II stomach)

e.g. Heart Cockle (Cartiidae), La La Siput (Veneridae), Meretrix (Veneridae)

Cordissum cardissa Cartiidae

Dosinia amphismoides Veneridae

Teredo sp. Terenidae

Tellina virgata Tellinidae

- Pteriomorphs  (reduced foot, filibranch gills (Oysters (orders Ostreida, Pectinida) are exceptions - they have eumellibranch gills with the exception of Plicatuloidea (superfamily)), mantle edges generally not fused, taxodont or dysodont hinge teeth)

 e.g. Green Mussel Perna sp. (Mytilidae), Hammer Oyster (Isognomonidae), See Hum Anadara sp. (Arcidae), File Shell (Limopsidae), Scallops (Pectinidae), Spiny Oysters (Spondylidae)

Lithophaga teres Mytilidae

Isognomon isognomon Isognomidae

Pinna bicolor Pinnidae

Spondylus niobarensis Spondylidae

A related species to Spondylus, the Comptopallium radula

Notes:

- filibranch is ancestral to eulamellibranch gills

- heterodont/schizodont/isodont/dysodont teeth is more derived than taxodont teeth

Important parts of the bivalves are:

Of the valves

- Hinge teeth: either cardinal or lateral; isodont/schizodont/heterodont/dysodont/taxodont

Taxodont hinge of Anadara antiquata Arcidae

- Umbo: a knobbly protuberance (determines dorsal)

- Lunule (typically anterior but the mouth position determines anterior/posterior)

- Estucheon (typically posterior)

- Periostracum - either secreted by the mantle edge or foot

- Pallial line, where the mantle edge is

- Pallial sinus, a groove where the siphons are retracted into

Anatomy

- Ligament: inner (lamellar), outer (fibrous); can be alivincular, duplivincular, parivincular, multivicular, either amphidetic (either side of the umbo; usually only for alivincular or dulivincular only) or opisthodetic (anterior of umbo; usually for parivincular or multivincular only); e.g. opisthodetic parivincular are typically of the heterodonts, multivincular opisthodetic are typically of the Isognomidae ("Hammer Oysters"), duplivincular amphidetic (Arcidae), alivincular amphidetic (Limopsidae),

- Gills: made up of lamellae with cillia (Protobranchs); when fused, form demibranches connected by tissue between lamella but not always so; might have cillary junctions (filibranch; Pteriomorphs); when filaments are fused with adjacent filaments, form interfilament junctions, exclusively NO cillary junctions (eulamellibranch; Heterodonts); typically one pair of ctenidia on each side of the visceral mass; each ctenidia with a descending and descending lamella for the eulamellibrach condition; Septibranch condition is a poorly-developed septum with vestigial gills but has tentacles on inhalant siphons to suck small prey up

- Adductor muscle - present most of the times in the anterior and posterior position (isomyarian/heteromyarian/monomyarian); typically one pair of adductor muscle(s) on each valve; for example, Green Mussels (Perna viridris) only has posterior adductor mussel, scallops have one large adductor (central) muscle (monomyarian)

Saccostrea cucullata Ostreidae with an adductor muscle scar

- Other retractor muscles 

- Mantle (inner, mid, outer folds; outer - secretory, may be sensory; mid - sensory, have tentacles, sometimes eyes; inner - muscular and attached to shells) with type A/B/C fusion

- Visceral mass which contains heart (2 auricles, 1 ventricle; open circulatory but certain families have haemoglobin and is 'bloody'), digestive organs (esophagus/ stomach - crystalline style, typhosole, sorting area/ intestines/ anus), reno-pericardial complex, gonads

- Periocardial complex

- Two ganglia (cerebro-pleural ganglia innervates palps, anterior adductor muscle, otocysts, part of mantle and visceral ganglia innervates gills, heart, pericardium, posterior adductor muscle, most mantle regions, siphons and pallial sense organs) 

- Byssus - secreted by foot typically

- Eyes - pallial (marginal or siphonal, innervated by mantle) or cephalic (inner demibranchs of ctenidia, innervated by cerebral ganglia)

- Siphon - for respiratory purposes/ suspension feeding

- Labial palps (2 pairs)/ palp probosoides (not always present)/ mouth; sometimes labial palps can be hypertrophied (such as in Scallops) to helps food items not 'fall out' while swimming

That was a spam of essential terms. Anyway, here're some photographs by Xin Rui during the practical.

Meretrix sp. ("La La") which is a heterodont. Photo source: Ong Xin Rui

The internal anatomy of the Meretrix sp. ("La La"), the same as above. For our practical session, we were required to draw the anatomy. Please note that the posterior and anterior ends should be exchanged. Photo source: Ong Xin Rui

Further reading
[1] About Glochidium/Lasidium larvae: http://mussel-project.uwsp.edu/evol/syst/larvae.html
[2] About hinge types: http://paleo.cortland.edu/tutorial/Bivalves/bivalvemorph.htm
[3] Pictures of bivalves: http://www.nmr-pics.nl/index.htm

I shall update this page again, after I have dug up my bivalve photographs. Everything makes more sense now after this class...

Please correct if you spot any errors. Information taken and summarized from Bivalve lecture notes.

Things we do in class - Fish dissection

Figure 1 - The Tilapia (Osteichthyes: Actinopterygii: Teleostei: Perciformes: Cichlidae: Tilapiine), before dissection. Instruments of the trade

Today marks the first time dissecting an animal during a practical session in "Topics in Aquatic Biodversity". Have watched people do it, and have heard people do it but have never done it myself before because it was never compulsory during biology classes in Junior College and in university, until now. It was quite an interesting experience, albeit frightening at first because it was fish but it really was not so bad.

*****

Fishes, a general introduction

Fishes are a diverse group of animals, that both live in marine and freshwater environments.

They are generally split into these extant groups:

• Hagfishes (Myxiniformes)
• Lampreys (Pteromyzontiformes)
• Jawed Fishes
  - Cartilagenous fishes
  - Bony fishes [ray finned - split into Sacropterygii and Actinopetrygii and lobe finned] 

Note: the Sacropterygii are further split into lungfishes, Tetrapods and Coelacanth; Actinopterygii further split into Neoptergyii and Chondrostei (bichirs, surgeons: which have some what ossification but are generally cartilagenous). Neopterygii is further split into gars (swim bladders function as lungs; heteroceral tail, ganoid scales), bowfins (similar to gars; which are actually able to breathe air, storing the air in its swim bladder connected to its digestive tract) and Teleostei

They are, however, paraphyletic, because any animal that "has a cranium, gill-bearing and lack limbs with digits" are lumped to this clade whereas the 'Tetrapods' are nested within this clade. Thus, it is not monophyletic.

Though, that is, besides the point. Most would be interested in fish as a commodity because it is important for food, which leads to problems of overfishing and is popular in the pet trade, which can lead to the proliferation of invasive animals, in the context of Singapore.

****

Morphology: the exterior and interior

note: the information presented here is learnt during lessons by Dr Tan Heok Hui

Just looking at the morphology of a fish can yield lots of interesting information. One can never divorce morphology from taxonomy and classification of fishes.

By looking at its exterior morphology (Figure 2), one can infer life history traits, habitat and food preferences about the fish based on certain generalizations -- but of course, there are always exceptions! Further, there are specialised structures, indicating some form of adaptations (e.g. barbels for sensory purposes).

1. Position of mouth: superior, terminal, inferior (and a whole suite of in-betweens)

2. Shape of body: torpedo, streamlined like the Tuna; oval shaped/ compressed laterally like the Mola Mola

3. Dentition: the type of teeth/ teeth plates (hooked, grazer-type, flesh-cutting, grinding; fused that is beak-like), the arrangement of the teeth (cartilagenous fishes have rows of teeth, unlike bony fishes), presence of pharyngeal teeth (to act as grips, not masticatory) which is located in the skull

4. Fins: shape of the five fins (ventral fins: pelvic, anal; dorsal fin(s); caudal fin, pectoral fins), whether it is fused or not; caudal fins can be truncate, emarginate, forked, deeply forked, rounded; pelvic fins can be fused; there can be one or two pectoral fins
5. Lateral line: can be complete or incomplete, from the top of the operculum to the (mid-) end of the peduncle; hyped-up lateral line systems with strong/weak voltage, the former for defense/finding prey and the latter for navigation.
6. Buccal cavity adaptations: in mudskippers it is used to store water, projectile expulsion in archer fishes, egg brooding in Osphronemidae/ Cichlidae/ Apogonidae/ Ariidae
7. Scales: Ctenoid/Cycloid (usually for higher fishes like the Teleostei; Ctenoid have a toothed outer edge, fishes with spiny rays as opposed to soft rays); Ganoid (garfishes, bichirs); Placoid (dermal/epidermal origins for Cartilagenous fishes)

Further, dissection to look at the internal morphology of the fish can further confirm the inferences (based on external morphology) such as the diet (gut content, length of gut), gender (male or female, by the gonads) and age (from otoliths in temperate fishes). Also, one can look at the gill rakers.

Figure 2 - Anatomy of a female fish. In a male fish, the ovary is replaced by the testicles.The bones are dorsal to the organs.
Source: http://en.wikipedia.org/wiki/Fish_anatomy

Figure 3 - Bamboo sharks (Chondrichthyes: Orectolobiformes: Hemiscylliidae), a male and a female. The males have a pair of claspers at the anal fins.

Figure 4 - Xin Rui's neat dissection area. She found two little crabs and one fish in the stomach of the predatory fish (second fish from the left).