The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water.
Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.

Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.

In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous).

Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species appear to be born sexually mature, although they are not fully grown.

Some fishes are hermaphroditic, an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.

Successful reproduction and in many cases defense of the eggs and young is assured by rather stereotyped but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.

Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in gravel beds where they themselves hatched (anadromous fishes). Others undertake shorter migrations from lakes into streams or in other ways enter for spawning habitats that they do not ordinarily occupy.

EVER wondered why Fido and Muffy prefer the toilet bowl to the water dish? Well, the truth could be that they’re just airheads.

A Swedish research scientist has discovered that the current generation of pedigree dogs, normally social and curious creatures by nature, are disinterested, shy and less responsive to commands than their ancestors.

The study found show-quality and “handbag” pooches were the most likely to lack the instincts of previous generations, which were bred for their strength, hunting and working abilities, rather than their looks.

Stockholm University ethologist Kenth Svartberg said personality changes could be seen in dogs that are only a few generations removed.

“Modern breeding practices are affecting the behaviour and mental abilities of pedigree breeds, as well as their physical features,” he said.

NSW University senior lecturer in genetics, Dr Alan Wilton, said it was a classic situation of “if you don’t use it, you lose it”.

“You can have lap dogs that are very intelligent. It’s just that, if they’re just sitting around doing nothing and you breed for many generations without selecting for intelligence, it is possible that their intelligence over time will diminish,” he said. “That’s what we expect is happening to some breeds.”

Selective breeding was also having an affect on dogs’ physical health.

The issue came to light last year in a British documentary, Pedigree Dogs Exposed, which detailed health problems among heavily interbred show dogs.

The show pressured the UK’s Kennel Club to consider changing its guidelines, in favour of less pronounced breed characteristics.

Master Dog Breeders and Associates CEO Julie Nelson agreed that many breeders valued appearance over skills, but said some breeds simply didn’t need them.

“The chihuahua was originally bred as a lap dog; all it needs to do is hang around the house. Same with dogs like pugs; they were never, ever intended to have any purpose, really, except to hang off people, to be companions,” she said.

According to the American Dental Society, 80% of dogs and 70% of cats show signs of oral disease by age three. This can lead to even more serious health problems including heart, lung and kidney disease. Ensuring your pet receives proper dental care from an early age is critical.

In addition to oral examinations and dental cleanings performed by your veterinarian, there are several things you can do to ensure the mouth of your dog or cat stays healthy.

Brushing at Home

Brushing your pet’s teeth daily helps prevent a multitude of oral and other health problems. It is best to introduce dental home care early with your new puppy or kitten. During your first veterinary visit, request a demonstration of how to properly and effectively brush your pet’s teeth.

Below are step-by-step instructions on how to brush your pet’s teeth at home.

1. Start with a healthy, comfortable mouth by having your veterinarian perform a dental cleaning. Existing problems may cause pain leading to an uncooperative dog or cat.
2. Start slowly by letting your pet become comfortable with you working inside their mouth with your finger. Gently rub along the gumline. Start at the front and move toward the back upper and then lower teeth and gums.
3. Pull his lip up to rub the outside of the teeth and gums.
4. Pull his head back gently to encourage him to open his mouth so you can clean the inside of his teeth.
5. Repeat on the opposite side of the mouth.
6. After your dog or cat becomes comfortable with your finger, place gauze over your finger and rub their teeth in a circular motion.
7. When your pet can handle the gauze, introduce a toothbrush during the next brushing session. It is important to make this switch because a bristled toothbrush cleans below the gumline where gauze or pads cannot reach.
8. Apply the bristles at a 45 degree angle to the surface of the tooth. Using small, circular motions, brush around the outside of the teeth ensuring the bristles get under the gumline. Brushing the sides of the teeth is not as important, as dogs and cats typically do not have tartar build-up between teeth like humans do.
9. Gradually add toothpaste designed for dogs or cats. Do not use people toothpaste or baking soda as both can upset your pet’s stomach.
10. Place your hand over your pet’s muzzle gently squeezing from the top.
11. Help keep your pet calm by praising your pet, speaking reassuringly and keeping the brushing sessions short. Remember, you will not always have a perfect teeth brushing session, but it’s important to be consistent and keep trying.

Other Considerations for a Healthy Mouth

Hard food and teeth cleaning biscuits can help keep your pet’s mouth clean in between brushings.

You should also be sure to regularly examine your pet’s mouth for signs of periodontal disease. Brownish teeth, consistently bad breath, swollen or bleeding gums and pus between the teeth and gums are all warning signs. If your dog or cat has these symptoms, consult your veterinarian.