No, it is not. Many people take verses such as these out of context, and use them and twist them to try and justify not believing in the Bible. However, they cannot truly understand the context of these verses, unless they actually READ the Bible, and not just the book of Leviticus, but the rest of the Bible as well.
9 ” ‘Of all the creatures living in the water of the seas and the streams, you may eat any that have fins and scales. 10 But all creatures in the seas or streams that do not have fins and scales—whether among all the swarming things or among all the other living creatures in the water—you are to detest. 11 And since you are to detest them, you must not eat their meat and you must detest their carcasses. 12 Anything living in the water that does not have fins and scales is to be detestable to you.
You must realize the purpose of this writing. This was not meant to apply to the whole world when it was written, but it was meant to be applied to specifically the Israelites. The reason for this is because God wanted to distinguish and separate the Israelites apart from every other nation on Earth. After God fulfilled this promise, Jesus declared that all foods are clean and may be eaten.
Mark 7:19 (NIV)
19 For it doesn’t go into his heart but into his stomach, and then out of his body.” (In saying this, Jesus declared all foods “clean.”) Peter was also given the words to say about declaring the food clean.
Acts 10:15 (NIV)
15 The voice spoke to him a second time, “Do not call anything impure that God has made clean.” Many ‘laws’ of the Old Testament change when Jesus comes to Earth. That is the misconception that so many people have about Christianity. They see verses like this with the shellfish, and only look at that verse, and use that as their basis for attack on Christianity.
Romans 10:4 (NIV)
4 Christ is the end of the law so that there may be righteousness for everyone who believes.
Galatians 3:24–25 (NIV)
24 So the law was put in charge to lead us to Christ that we might be justified by faith. 25 Now that faith has come, we are no longer under the supervision of the law.
Ephesians 2:14-18 (NIV)
14 For he himself is our peace, who has made the two one and has destroyed the barrier, the dividing wall of hostility, 15 by abolishing in his flesh the law with its commandments and regulations. His purpose was to create in himself one new man out of the two, thus making peace, 16 and in this one body to reconcile both of them to God through the cross, by which he put to death their hostility. 17 He came and preached peace to you who were far away and peace to those who were near. 18 For through him we both have access to the Father by one Spirit.
The law of shellfish, (which only applied to the Israelites in the first place), is a perfect example of one of these laws that changed when Christ came to Earth. I hope this answers your question!