Very simple-I look it up in the Bible:
Which Animals Does the Bible Designate as 'Clean' and 'Unclean'?
God reveals which animals—including fish and birds—are suitable and unsuitable for human consumption in Leviticus 11 and Deuteronomy 14. Although the lists aren't exhaustive, He reveals guidelines for recognizing animals that are acceptable for food.
God states that cud-chewing animals with split hooves can be eaten (Leviticus 11:3; Deuteronomy 14:6). These specifically include the cattle, sheep, goat, deer and gazelle families (Deuteronomy 14:4-5). He also lists such animals as camels, rabbits and pigs as being unclean, or unfit to eat (Leviticus 11:4-8). He later lists such "creeping things" as moles, mice and lizards as unfit to eat (verses 29-31), as well as four-footed animals with paws (cats, dogs, bears, lions, tigers, etc.) as unclean (verse 27).
He tells us that salt and freshwater fish with fins and scales may be eaten (verses 9-12), but water creatures without those characteristics (catfish, lobsters, crabs, shrimp, mussels, clams, oysters, squid, octopi, etc.) should not be eaten.
God also lists birds and other flying creatures that are unclean for consumption (verses 13-19). He identifies carrion eaters and birds of prey as unclean, plus ostriches, storks, herons and bats.
Birds such as chickens, turkeys and pheasants are not on the unclean list and therefore can be eaten. Insects, with the exception of locusts, crickets and grasshoppers, are listed as unclean (verses 20-23).
Why does God identify some animals as suitable for human consumption and others as unsuitable? God didn't give laws to arbitrarily assert control over people. He gave His laws (including those of which meats are clean or unclean) "that it might be well" with those who seek to obey Him (Deuteronomy 5:29).
Although God did not reveal the specific reasons some animals may be eaten and others must be avoided, we can make generalized conclusions based on the animals included in the two categories.
In listing the animals that should not be eaten, God forbids the consumption of scavengers and carrion eaters, which devour other animals for their food.
Animals such as pigs, bears, vultures and raptors can eat (and thrive) on decaying flesh. Predatory animals such as wolves, lions, leopards and cheetahs most often prey on the weakest (and at times the diseased) in animal herds.
When it comes to sea creatures, bottom dwellers such as lobsters and crabs scavenge for dead animals on the sea floor. Shellfish such as oysters, clams and mussels similarly consume decaying organic matter that sinks to the sea floor, including sewage.
A common denominator of many of the animals God designates as unclean is that they routinely eat flesh that would sicken or kill human beings. When we eat such animals we partake of a food chain that includes things harmful to people.
As nutritionist David Meinz observes: "Could it be that God, in His wisdom, created certain creatures whose sole purpose is to clean up after the others? Their entire 'calling' may be to act exclusively as the sanitation workers of our ecology. God may simply be telling us that it's better for us believers not to consume the meat of these trash collectors" (Eating by the Book,1999, p. 225).
The following list, based on Leviticus 11 and Deuteronomy 14, identifies many of the animals God designates as clean and unclean. The list uses their common names.
Mammals That Chew the Cud and Part the Hoof
Cattle (beef, veal)
Sheep (lamb, mutton)
Fish With Fins and Scales
Black pomfret (or monchong)
Herring (or alewife)
Mahimahi (or dorado, dolphinfish[not to be confused with the mammal dolphin])
Perch (or bream)
Pike (or pickerel or jack)
Pollack (or pollock or Boston bluefish)
Sardine (or pilchard)
Silver hake (or whiting)
Smelt (or frost fish or ice fish)
Snapper (or ebu, jobfish, lehi, onaga, opakapaka or uku)
Trout (or weakfish)
Tuna (or ahi, aku, albacore, bonito
Turbot (except European turbot)
Birds With Clean Characteristics
Sparrow (and other songbirds)
Types of locusts that may include crickets and grasshoppers
* In the King James Version, Leviticus 11:18 and Deuteronomy 14:16 list "swan" among unclean birds. However, this seems to be a mistranslation. The original word apparently refers to a kind of owl and is so translated in most modern Bible versions.
Animals With Unclean
Pig (hog, bacon, ham, lard, pork, most sausage and pepperoni)
Llama (alpaca, vicuña)
All insects except some in the locust
Marine Animals Without Fins and Scales
Sturgeon (includes most caviar)
Crayfish (crawfish, crawdad)
Birds of Prey, Scavengers and Others