Many ayi's will go shopping for the family/families they work for, which could pose a problem when it comes to freshness. Most Chinese tend to buy fish at the market not looking, nor knowing how to identifying fresh fish. Chinese also buy fish though the scales or other parts may be infected. The belief here is that once cooked, the problem is gone!

Below you can find an instruction you can print for your ayi. The writing and translation has been provided by Expat 2 Expat Co., Ltd.

How to identify fresh fish.
如何鉴别新鲜的鱼类

The term 'fresh' fish will mean different things to different people and different cultures.
“新鲜的”鱼一词对不同的文化和不同的人来说有意味着不同的事物

1. To many people fresh simply means not frozen.
对很对人来讲，新鲜简单的意味着不是冰冻的。
2. To others it means 'at its peak'.
对其他人，新鲜意味着“在其颠峰时刻”
3. To the Japanese it means less than a day old, as in less than 24 hours after it was caught. This is often referred to as being 'sashimi quality' . However for it to be truly of sashimi quality it must have been caught, killed, gutted and stored in a certain way before sale.
对日本人，意味着被捕捉的时间少于一天，也就是24小时以内。这也通常被称为“刺身质量(可以吃的生鱼片)”，然而，要成为真正意义上的刺身，在出售前，必须以特有的方式捕捉、杀死、去除内脏、保存。
4. To a professional chef it will usually (and hopefully) mean being served within three days of being caught.
对专业级的厨师来讲，通常（和希望）3天以内被捕捉的来做菜

Fresh? There are so many factors that determine fresh when it comes to fish.
新鲜？对鱼类来讲，很多因素来决定着其新鲜程度

1. Fish should always be gutted and gilled as soon as it is caught, so any bacteria held in these areas cannot permeate into the flesh as it breaks down (it also ensures a better flavour and aroma).
鱼类通常应该在被一捕捉到的时候就应该去去除内脏，这样，可以防止在破坏其内脏时，这些内脏中的细菌侵入鱼肉中(这也确保更好的口感和风味)。
2. A fish may be only two days old but if it is has not been stored correctly it might as well be two weeks! Experts agree, that for every hour a freshly caught fish is not stored on ice, it loses one day of shelf life. So a fish not chilled for four hours is equivalent in quality to a five day old fish that has been kept on ice.
一条鱼有可能捕捉时间仅2天，但是如果没有真确的保存，有可能和2周的鱼差不多。专家认同，新鲜捕捉的鱼类，如果晚一小时存储在冰块上，它将损失一天在货架上的存放期。所以，4个小时没有冷冻的鱼在质量上相当于在大概在冰块中已经保存了5天的鱼。
3. If a fish is stored correctly, (kept on ice) from the time it is caught, it has a useable life of up to ten days. However this is rarely the case and one should use the fish of course as soon as possible. Besides the fact it tastes so much better, one must also remember the health benefits and staying safe from food poisoning.
如果存储的方法正确，从被捕捉的那一刻起(保存在冰块中)，那么它有高达10天的保质期。然而，这种情况很罕见，但还是应该尽快使用。 除了其较好的口感外，我们还应重视住它对健康的影响，防止食物中毒
If you have frozen fish, once thawed you should use it within 24 hours - 48 at the most.  DO NOT REFREEZE FISH!
如果你有冰冻的鱼，一旦解冻，应该在24小时内使用 — 最多不超过48小时。千万不要重新冷冻。
4. How to tell how fresh fish is? With filleted fish it can be very difficult, one must rely on our senses of smell and touch.
如何来辨别什么样的鱼是新鲜的？对于已经切片的鱼来讲这非常困难，我们必须依靠嗅觉和触觉来判断、
When lightly pressed the flesh of 'fresh' fish should be quite resilient and bounce back, the older it gets the more likely it is that the indent will remain or slowly bounce back.
当轻压“新鲜的”鱼肉时，它们应该富有弹性，压触后能迅速弹回，对于那种不新鲜的，则压痕不容易消失，而且回弹缓慢
It should of course smell fresh, the more it smells like 'fish' the older it is. The fresher it is the less unpleasant aroma there will be.、
它当然应该味道新鲜，鱼腥味越重，则越不新鲜。如果越新鲜，则他们有更少的令人难闻的味道。
Always presuming one can be allowed to smell and touch prior to purchase, or one must rely on the supplier and maybe the use by date if packaged.
通常，假定我们购买前可以嗅或者摸，或者我们必须依靠供应商及包装上的日期。
5. For whole fish look for a pleasant aroma (someone once wrote that, fish should smell of the sea, be briny in aroma . . . by the time it smells of fish it is too late! )
对于整条鱼来讲，注意其让人愉快的味道(有人曾经记载，鱼应该有大海的味道，海水的那种味道•••，如果已经能闻到鱼的味道，那已经为时已晚)
flesh that is resilient
肉富有弹性
plentiful scales that are not dried up
鳞片丰富而且无干涸
the body being covered in sea slime
身体附着有海水粘液
bright, "shiny", bulging eyes
明亮，“有光泽”，眼球鼓胀
the gills should be bright and / or red and free from any yeasty aroma and slime (slime in the gills is usually a bacterial slime - not good!)
内脏应该有光泽和(或)红色，无任何发酵的气味和粘液(内脏中的粘液通常都是细菌粘液———不好!)
If a fish is gutted, the blood along the backbone should be brightly coloured, if it's not the fish is not fresh.
（如果一条鱼被剖开，血顺着脊椎骨的颜色应该是鲜艳的；如果不是，则不新鲜）

The older the fish, the lower the quality, the less the above will apply. For example all other signs might be present but.
鱼越不新鲜，其质量越低，上述的描述越不明显。如有其他的特征，如下，
1. The eyes might be slightly sunken - indicating the fish is 'fresh' but not the freshest.
眼珠少向下陷—--虽然“新鲜”但不是最新鲜的那种
2. No sea slime on the body, this can indicate that it's very fresh but it's just been handled with a cloth and wiped off.
无海洋粘膜覆盖，这可能很新鲜但有可能刚被擦拭过
What it all comes down to is one must use one's owns judgment, rely on one's senses (including common sense!) and what are you buying the fish for?
当遇到这些这种情况时，个人要运用自己的判断力，依靠某人的感官（包括通常的感觉）以及买来的鱼用来做什么用。
If it's for sashimi it must be almost alive!
如果购买金枪鱼，则必须几乎是活鱼。
If it is for poaching it must be fresh, fresh
如果垂钓，必须是非常新鲜的，
If it is for frying, BBQ etc then as long as the fish smells ok, it probably is and will taste fine
如果用来炸、烧烤等，则只要闻起来味道还可以，基本上尝起来也应该不错。
Food safety
食品安全

I cannot stress enough though, that even fish straight out of the sea does NOT guarantee against food poisoning! If the fish contains certain pathogens (food poisoning bacteria) or if it has been feeding near sewerage outlets (and many fish do!) then even cooking them is still likely to give you a bit of an stomach upset. All one can do, like anything in life is to stay as safe as possible.

但这一点我无法给出足够建议，即便是刚从大海里捕捉的鱼也难以保证无食物中毒。如鱼的体内包含有某种病原体（致使食物中毒的细菌），或者他们吃了下水道的排放物(很多鱼都会这样).即便是经过烹调，有可能引起食物中毒。就如同生活中的其他事情一样，我们能做的，就是尽可能保持安全。